Caught My Eye…

The Cambridge Sweetener Study: What It Actually Says (And What It Doesn’t)

A study came out on July 16, 2026 from the Medical Research Council Toxicology Unit at Cambridge, published in Molecular Systems Biology. It’s already getting headlines like “sweeteners destroy your gut bacteria” which is... not quite what it found. Here’s the real version.

The researchers took 25 species of gut bacteria and exposed them to 39 commonly used sweeteners in a lab setting. Not in humans, in lab cultures. What they found: about 75% of the sweeteners they tested changed the growth of at least one gut bacterial species. Some slowed the growth of beneficial bacteria. The effects varied a lot depending on which sweetener, which bacteria, and what else was present.

The most dramatic finding was when they combined a compound called isosteviol (which is derived from the stevia plant but isn’t actually used as a consumer sweetener, it doesn’t have a sweet taste, which makes some of the headlines misleading) with the antidepressant duloxetine. That combination significantly suppressed two bacteria linked to blood sugar regulation and gut health: Roseburia intestinalis and Parabacteroides merdae.

The finding that “sweeteners can interact with gut bacteria, and those effects can be amplified by medications” is genuinely interesting and worth knowing. The “sweeteners destroy your gut” headline is overstating lab-dish research that hasn’t been tested in humans.

What gastroenterologists are actually saying in 2026: the effects are sweetener-specific (not all sweeteners behave the same), dose matters (moderate intake in most healthy adults shows minimal disruption), and individual variation is significant, your response depends on your existing gut composition. Stevia-based sweeteners appear least likely to affect microbiome composition. High-dose saccharin has links to glucose intolerance in animal models. Sucralose and aspartame at moderate doses show minimal disruption in most human studies.

The bigger point: this is one more piece of evidence that what looks “calorie-free” isn’t necessarily effect-free. The gut microbiome is sensitive to a lot of things, and sweeteners are apparently one of them.

Your Skin Is Ageing Before You Can See It. A July 2026 Study Just Showed What That Looks Like.

This one is specifically relevant for anyone who’s read the collagen short dive, the sunscreen guide, or any of the skin longevity content I’ve covered.

A study published in ACS Nano on July 16, 2026, from Hiroshima University, developed a technique that can detect the very earliest damage to collagen in skin, before any of it is visible under conventional imaging. The finding: collagen doesn’t start falling apart visibly first. It starts losing its precise molecular organisation first. The structure begins to disintegrate at the smallest scale before it shows up as thinner fibres, fragmentation, or visible wrinkling.

To put it simply: the skin can look completely intact in a standard scan while something has already started happening underneath, at a level too small for current tools to see.

Dr. Barbara Kubicka described it as:

Which is a very elegant summary of why the sunscreen and SPF conversation matters before you can see any damage.

What this doesn’t change: we don’t have treatments that target this pre-visible stage yet. The imaging technique is not clinically available. This is foundational research, not a diagnostic tool you can book.

Prevention looks like nothing happening. That’s the whole point of it.

Why You Can’t Sleep When It’s Hot: The Actual Biology (And What To Do)

It’s a heatwave. A significant portion of people reading this are probably sleeping terribly right now. So here’s the biology of why, and then the interventions that are actually backed by sleep research rather than just “have you tried a fan.”

Your body needs to drop its core temperature by approximately 1°C to fall asleep and stay asleep. This drop is regulated by your circadian clock and is a physical requirement for entering deep, slow-wave sleep. In normal conditions, this happens through a process called distal vasodilation; blood is sent to your hands and feet, where heat radiates away from your body, cooling your core.

When the room is too warm, this process is physically blocked. Your body can’t offload heat through the skin efficiently enough. The sleep attempt fails not because your brain is doing something wrong but because the physical conditions for deep sleep don’t exist in a hot room.

The research on optimal sleep temperature: between 16–19°C (60–67°F) for most adults. This is significantly cooler than most people keep their bedrooms. Above 24°C, research shows measurable increases in nighttime waking and reduced slow-wave sleep.

For women in the luteal phase of their cycle, this is compounded further, progesterone raises baseline body temperature by 0.3–0.7°C, meaning the threshold for too-hot is lower in the two weeks before a period. Summer + late luteal phase is the combination most likely to destroy sleep quality.

What the sleep science actually supports for heatwaves:

• Close blinds all day to prevent solar heat gain, the room is cooler before bed if it was kept cool during the day

• Open windows in the evening when outside air is cooler than inside air, close them in the morning before it heats up again

• A lukewarm (not cold) shower 60–90 minutes before bed counterintuitively, this helps. Warm water on the skin accelerates peripheral vasodilation, which speeds up the core cooling process. A cold shower actually triggers vasoconstriction, which keeps heat in

• A fan to accelerate evaporative cooling from sweat on the skin. This is the most effective bedroom intervention without AC

• Lightweight bedding; cotton and linen wick and dry faster than synthetic fabrics, keeping the microclimate next to your skin cooler

• Don’t eat a large meal close to bedtime in a heatwave as digestion generates heat internally, adding to the core temperature problem

The one most people get wrong: cold showers right before bed feel good but can temporarily raise arousal and make it harder to fall asleep because of the vasoconstriction response. Lukewarm, not cold.

Late-Night Eating Under Stress Makes Your Gut Worse. A New Study Found Exactly Why.

This finding from May 2026 is sitting quietly in the research and hasn’t gotten much attention, but it directly connects several things I’ve covered.

Chronic stress is already known to affect gut health, through the gut-brain axis, elevated cortisol changes gut motility, bacterial composition, and gut lining integrity. What this new study added is a specific amplification: people under high chronic stress who also ate late at night had measurably worse gut outcomes than people who were stressed but ate earlier in the day.

The mechanism is about circadian biology. The gut microbiome has its own circadian rhythm, different bacterial species are active and inactive at different times of day, and the composition of the gut environment shifts across a 24-hour cycle. When eating is pushed to late at night, it conflicts with the gut’s circadian programme, which is expecting rest and repair processes rather than active digestion. Combined with chronically elevated cortisol (which is already disrupting the gut environment), late-night eating appears to compound the gut damage from stress rather than just adding to it independently.

This is relevant for anyone who stress-eats late at night (which is extremely common. Stress increases appetite, particularly for high-carbohydrate foods, and cortisol peaks in the evening under chronic stress). The gut was already dealing with the cortisol. Adding late digestion on top of it gives it less recovery time.

The information in this post is for educational and informational purposes only. None of the above constitutes medical advice. Always consult a qualified healthcare professional for personal health concerns.

Between Saturdays is a weekly research roundup from Simply Salvia. Four things from science and wellness worth knowing about. If someone sent this to you, you can subscribe here.

Detailed Readings:

Sweeteners slow growth of important gut bacteria in lab tests

Common xenobiotics modulate gut microbial responses to low-calorie sweeteners in vitro

Scientists detect invisible early signs of skin aging

Can’t sleep in the heat? These 8 tricks could save your night

Late-night eating plus stress doubles the risk of bowel problems

I’m bloated like four days a week. My stomach goes from flat in the morning to “are you pregnant” by evening for absolutely no reason I can identify. I’ve had random stomach pain that comes and goes. I’ve had weeks where I couldn’t poop and weeks where I couldn’t stop. I’ve Googled “why is my stomach always weird” more times than I’d like to admit.

And apparently I’m not alone, because #hotgirlshaveibs has over 112 million views on TikTok.

That number is funny to say out loud, but it’s also telling us something real: gut problems are so common in young women that we made a whole meme about it. Bloating, constipation, random stomach pain, IBS, these are being treated as an inherent part of having a female body, like cramps. Just a thing that happens. Nothing to do about it.

Except there’s actually a lot of research on why this is happening. And it’s more interesting than “women just have sensitive stomachs.” There’s a reason IBS affects women at twice the rate it affects men. There’s a reason your gut feels totally different in different weeks of the month. There’s a reason stress literally gives you stomach pain.

This short dive is the explanation your body has been waiting for. What’s actually going on, why it’s specifically worse for us, and what you can actually do about it.

1. Your Gut and Your Brain Are Basically in a Group Chat

2. Why Women Specifically Got the Worst Deal Here

3. What "Gut Health" Actually Means (And What It Doesn't)

4. The Bloating Chapter (Finally)

5. What to Eat (And What's Probably Making Things Worse)

6. Your Gut and Your Skin Are Talking To Each Other

7. The Cycle-Aware Gut Protocol

8. The Practical Guide: Probiotics Decoded and the Daily Habits

9. The Short Version of Everything

Chapter 1: Your Gut and Your Brain Are Basically in a Group Chat

Okay so picture this: you have a big exam coming up. Or a difficult conversation you’re dreading. And your stomach feels it before anything has even happened. The knot, the sudden need to run to the bathroom, the weird nausea that shows up when you’re stressed. That’s not a coincidence or a personality quirk. That’s biology.

Your gut and your brain are connected by something called the gut-brain axis, which is basically a direct communication highway between the two of them, running through a nerve called the vagus nerve. They’re constantly texting each other. The brain sends signals down to the gut (this is why stress and anxiety mess with your digestion). The gut sends signals back up to the brain (this is why gut problems affect your mood). It goes both ways, constantly.

Here’s what makes this even more interesting: your gut has its own nervous system. Like, an independent one. It has more nerve cells than your spinal cord, around 500 million of them and it can operate semi-independently of the brain. Scientists sometimes call it the “second brain,” which sounds dramatic but is actually just anatomically accurate. The gut is not just a tube that moves food. It’s a complex sensory organ that’s in constant conversation with everything else.

And living inside that gut? About 38 trillion bacteria, fungi, and other microorganisms that collectively make up your gut microbiome. These aren’t just sitting there. They’re actively producing neurotransmitters including about 90–95% of the body’s serotonin (yes, the mood chemical, mostly made in your gut, not your brain), GABA (the calming neurotransmitter your anxiety chapter covered), and dozens of other compounds that affect how you feel mentally and physically. The gut microbiome is, in a very real sense, part of your emotional regulation system.

This is why “gut health” isn’t a wellness trend invented to sell supplements. It’s a genuinely important area of research with implications that go way beyond digestion. When your gut bacteria are diverse and well-fed, the whole system tends to work. When they’re disrupted through a bad diet, antibiotics, chronic stress, not sleeping, the effects ripple outward into your mood, your skin, your hormones, and yes, your digestion.

The #hotgirlshavestomachissues meme exists because the gut-brain axis is more active in young women than most of us realise, in a hormonal environment that specifically makes it more reactive. Which brings us to chapter 2.

Chapter 2: Why Women Specifically Got the Worst Deal Here

Women are twice as likely to have IBS as men. Twice. And symptoms peak between ages 18 and 39.

For a long time, medicine didn’t have a great explanation for this. The assumption was that women were more likely to report symptoms, or that psychological factors explained the gap, or just that women had more “sensitive” guts in some vague way that nobody could really explain.

Then in December 2025, researchers at UC San Francisco published a study in the journal Science that finally gave us the mechanism. And it’s estrogen.

But not in the way you might think.

The estrogen finding that changed everything

The researchers were looking at a specific type of cell in the colon called L-cells. These cells normally release hormones related to appetite and gut movement. What the researchers found was that estrogen binds to receptors on these L-cells, and when it does, it triggers the release of a hormone called PYY, which then tells nearby pain-sensing cells to flood the area with serotonin.

Serotonin in the gut (not the mood version, a different mechanism) activates the pain-sensing nerve fibres that send “something’s wrong here” signals to your brain. So the chain looks like this:

To prove it was actually the estrogen doing this, they gave male mice estrogen doses equivalent to female levels. The male mice’s gut pain sensitivity immediately increased to match that of females.

Here’s the second part that explains so much: estrogen also caused those L-cells to produce more receptors for the byproducts of gut bacteria fermenting food specifically the fermentation of things like onions, garlic, beans, and wheat (what dietitians call FODMAPs). So estrogen isn’t just making the gut more pain-sensitive in general. It’s also making it more reactive to specific foods that produce gas and fermentation.

This is the mechanism behind two things that confuse a lot of women:

• Why your gut reacts to foods that don’t bother other people — estrogen has specifically made your gut more sensitive to those fermentation byproducts

• Why gut symptoms often change across your cycle — because estrogen levels change across your cycle, and so does gut sensitivity

The cycle-bloating connection

This is where it gets really specific and really useful.

In your follicular phase (after your period ends, leading up to ovulation), estrogen is rising. The gut is more sensitive because of the mechanism above. Some women notice their stomach is more reactive in this phase than they expect.

Around ovulation, estrogen peaks, this is when the gut is at its most sensitive, and some women have their worst gut pain here even though they don’t associate it with the premenstrual window at all.

In the luteal phase (after ovulation, the two weeks before your period), progesterone takes over. And here’s what progesterone does to your gut: it slows everything down. Literally. It slows the contractions that move food through your intestines. This is why constipation is specifically worse in the two weeks before your period, progesterone is basically putting the brakes on your digestion.

Then as you get close to your period, prostaglandins kick in, the compounds that drive uterine contractions to start your period. They also affect your intestines. Which is why, right when your period starts, many women swing from constipation to diarrhea. Your intestines are responding to the same signal your uterus is.

And throughout all of this: the composition of your gut microbiome itself changes across your cycle. The bacteria that thrive in different hormonal environments are actually different bacteria, which is why your stomach can feel so variable month to month even if you’re eating the same things.

The anxiety loop

There’s one more piece that rounds out the “why women” picture. Women experience anxiety at twice the rate of men (covered in the anxiety short dive). And anxiety directly activates the gut-brain axis. The stress response tells the gut to change how fast things move, which changes the bacterial environment, which changes which signals go back to the brain.

This is why the TikTok meme exists. It’s not a coincidence that “hot girls have stomach issues” overlaps almost exactly with “young women have the worst mental health of any demographic.” The anxiety is activating the gut. The gut is feeding back into the anxiety. It’s a loop.

And once you understand that the loop exists, you can start intervening at both ends of it.

Chapter 3: What “Gut Health” Actually Means (And What It Doesn’t)

“Gut health” has become one of those wellness terms that means everything and nothing simultaneously. Let’s sort it out.

What it actually means

Your gut microbiome is healthy meaning it’s diverse, when it contains a wide variety of bacterial species that are collectively able to:

• Ferment dietary fibre into short-chain fatty acids (these are the compounds that reduce inflammation, maintain the gut lining, and communicate with the immune system)

• Metabolise estrogen properly through the estrobolome (so hormones are cleared correctly rather than recirculating)

• Produce adequate GABA and serotonin precursors for the gut-brain axis

• Maintain the integrity of the gut lining (preventing the “leaky gut” situation where compounds that shouldn’t cross into the bloodstream do)

All of these are extremely common in the 15–35 age group.

What “gut health” doesn’t mean

It doesn’t mean your gut is a glass that you can “clean” or “detox.” Your gut is not dirty. You cannot flush it. Juice cleanses and “gut reset” programmes don’t remove bacteria, they temporarily change the environment, and your bacteria largely return to their previous composition within a few weeks because bacteria adapt quickly.

It doesn’t mean that fermented food alone fixes everything. Kefir is great. It is not going to compensate for a diet with almost no fibre.

It doesn’t mean every gut problem has a dietary solution. Some gut conditions like Crohn’s disease, ulcerative colitis, coeliac disease, SIBO, gastroparesis, are medical conditions that require medical diagnosis and management. Persistent, severe, or new-onset gut symptoms that affect your quality of life should be investigated by a doctor, not just managed with probiotics. The TikTok meme normalises talking about gut issues, which is good. It should not normalise ignoring symptoms that need investigation.

The fibre gap you probably have

The single most impactful thing for gut microbiome diversity is dietary fibre specifically the variety of fibres that comes from eating a range of plant foods. Current recommendations are 25–38g of fibre daily. Most people in Western countries eat less than half of this.

This isn’t about eating more salad. It’s about variety. Different plant fibres feed different bacterial species. The research consistently shows that the most diverse gut microbiomes come from people who eat the widest variety of plant foods and not the people who eat the most of one specific “gut health” food. The goal is 30 different plant types per week, including vegetables, fruits, legumes, nuts, seeds, herbs, and wholegrains. This sounds like a lot until you realise that three different colours of bell pepper count as three, and a handful of mixed seeds counts as several.

That’s Part 1. Part 2 is where I get into the specific stuff: the bloating chapter with what actually makes it worse and what actually helps, what to eat (and stop eating), how your gut and your skin are connected in ways that explain a lot, the cycle-aware gut protocol, and the practical guide to probiotics that doesn’t just say “take a probiotic.”

So now you know what’s actually going on. Your gut and your brain are in a constant two-way conversation that affects your mood, your skin, your digestion, and your hormones. Estrogen specifically makes your gut more pain-sensitive through a mechanism that researchers only fully mapped in December 2025, meaning the “why does this hurt me more than everyone else” question finally has a real answer. And “gut health” isn’t a vibe. It’s a specific biological state with specific things that support or disrupt it.

Part 2 is the practical half.

Chapter 4 is the bloating chapter. The actual causes of each type of bloating (they’re different), what makes them worse, what the research says actually helps, and why most of the bloating advice you’ve seen is addressing the wrong thing.

Chapter 5 is what to eat. Not a meal plan. The specific foods and eating patterns with actual research behind them for gut health and the specific things that are probably making your gut worse right now.

Chapter 6 is the gut-skin connection, for anyone whose skin problems haven’t fully responded to topicals. The route from gut bacteria to estrogen to jawline acne is documented, and this is the chapter that explains it properly.

Chapter 7 is the cycle-aware gut protocol. What to do differently in each phase because your gut is genuinely different in each phase.

Chapter 8 is the practical guide: probiotics decoded (the strain thing matters and most people don’t know this), what supplements actually have evidence, and the daily habits that make the most difference.

Subscribe to read Part 2 →

Sources & Further Reading

UCSF — Do Hormones Explain Why Women Experience More Gut Pain? December 2025

Venkataraman et al. A cellular basis for heightened gut sensitivity in females — Science, December 2025

MedicalXpress — IBS affects women more than men — here’s why, October 2025

Digestive Diseases and Sciences — It’s a Women’s World: Sex Differences in IBS, March 2025

Mayo Clinic Proceedings — Sex and Gender Differences in Functional Gastroenterologic Disorders, 2021

Evelyn Health — PMS and gut health: what your digestive symptoms are telling you, June 2026

PMC meta-analysis. Effects of probiotics on depression and anxiety in clinically diagnosed patients, 2025

Frontiers in Microbiology. Psychobiotics in mental health: gut-brain axis insights, March 2026

Osprey Polyclinic. The gut-hormone connection for women, February 2026

Fortune — The hot girls have stomach issues social media trend makes sense, 2023

Caught My Eye…

Scientists Just Found the Brain’s Built-In Focus Filter And What Interferes With It

Most conversation about focus and attention in the wellness space ends up at the same place: reduce screen time, try meditation, maybe try magnesium. That advice isn’t wrong, but it lacks a mechanism. A finding published in June 2026 provides one.

Scientists have discovered a tiny group of neurons in an ancient brain region that acts like a built-in focus filter, helping the brain ignore distractions.

The neurons identified are located in a region called the zona incerta, a small area in the brainstem that’s evolutionarily ancient, present across many mammalian species. This cluster acts as a gating mechanism for attention: when activated, it helps the brain filter out irrelevant sensory information and sustain focus on a task. When it’s underactive or disrupted, attention becomes more fragmented and the brain is more easily pulled toward new stimuli.

What’s interesting about this from a women’s health perspective: the zona incerta has connections to several hormonal and stress-regulatory systems, including pathways that interact with estrogen and cortisol. This is consistent with the well-documented experience that attention and focus fluctuate across the menstrual cycle, particularly in the late luteal phase when estrogen is falling and cortisol sensitivity is higher. The neurological basis for those fluctuations is still being mapped, but this finding suggests the attention-gating system is more intertwined with the hormonal environment than the “just work harder” framing of focus difficulties implies.

The finding also has implications for understanding why constant notification environments are so cognitively costly. Every notification is a competing input that the focus-filter circuit has to evaluate. In an environment of high-frequency, high-novelty stimuli, the filter is never given the uninterrupted window it needs to sustain deep focus, which is less about willpower and more about the mechanics of how this circuit operates.

Protein Timing Matters More Than Most Nutrition Content Acknowledges

This builds directly on the protein breakfast research covered in a previous post and the weight loss short dive, but with a new piece that adds specificity.

The protein-for-satiety story has been well-established: protein is the most satiating macronutrient, it triggers the strongest GLP-1 and PYY response, it preserves muscle during a calorie deficit, and it has the highest thermic effect. All of that holds. What’s been getting more research attention recently is whether when you eat protein across the day affects outcomes beyond total daily intake.

The emerging picture from 2025–2026 research: protein’s satiety effects are most powerful when it’s distributed across all meals rather than concentrated in one sitting. This matters because a common pattern, particularly in women following dietary restriction is to eat very little protein through the morning and early afternoon, then consume the majority at dinner. Research on protein distribution suggests this pattern underutilises protein’s appetite-suppressing and muscle-building effects compared to an even distribution of 25–30g across three meals.

There’s a muscle synthesis angle to this too: muscle protein synthesis (the process by which dietary protein is incorporated into muscle tissue) appears to be more efficient when protein is consumed at regular intervals throughout the day rather than in one large dose. The muscle-building machinery seems to reach a saturation point with single large protein doses, meaning that 90g at one meal is less effective than 30g at three meals for the same protein total.

Sleep Duration, Deep Sleep, and Cancer Risk. What the Research Says Without the Alarm

This one needs to be framed carefully, because the headline version of it ; “poor sleep causes cancer” is both an oversimplification and, in that form, more anxiety-inducing than informative. Here’s what the research actually says.

Chronic sleep disruption specifically, consistently sleeping fewer than 6 hours per night, or having severely fragmented sleep for extended periods is associated in observational studies with elevated risk of several cancers, including breast cancer. The proposed mechanism involves melatonin: melatonin is produced during darkness and suppresses the proliferation of certain cancer cells, including oestrogen receptor-positive breast cancer cells. Chronic light exposure at night and severely disrupted sleep reduce melatonin production, removing this suppressive effect.

A July 2026 research finding added a specific cellular mechanism: researchers identified a previously overlooked mechanism of brain cell death that appears to play a major role in Alzheimer’s disease and frontotemporal dementia but in doing so, also illuminated the deep sleep clearing processes (the glymphatic system, which clears cellular waste overnight) that are relevant to a broader set of conditions when chronically disrupted.

Two things are worth being clear about: the observational associations between sleep and cancer risk are real but modest in most studies, and they don’t establish causation. People who chronically sleep fewer than 6 hours often have other health and lifestyle factors that independently elevate risk. And the mechanism: melatonin suppression of cancer cell proliferation is one pathway among many.

What the research does consistently support, without overstating it: maintaining regular sleep hours, keeping the sleeping environment dark (blocking artificial light), and prioritising 7–8 hours of uninterrupted sleep are all independently supported interventions with the best evidence for multiple health outcomes simultaneously. The cancer risk dimension adds an additional layer to what is already a comprehensive case for sleep as a foundational health behaviour, not a reason for alarm, but a reason to take the priority of sleep seriously in a culture that routinely treats it as optional.

The Social Media and Body Image Research Is Getting More Specific and More Useful

The “social media is bad for body image” finding has been replicated so many times it has almost stopped being news. What’s becoming more useful in the 2025–2026 research is the specificity, which types of social media use, which types of content, and which individuals are most affected, in ways that allow more targeted and actionable guidance than “use social media less.”

What the recent research has been finding:

Passive consumption: scrolling without interaction, comparing without engaging, produces significantly worse body image outcomes than active engagement (posting, commenting, creating). This distinction matters because the guidance “use social media less” ignores that some forms of use are considerably more harmful than others. Passive scrolling through appearance-focused content in a low-mood state is the highest-risk pattern. Creating content, engaging in communities, and active participation carry much smaller (and in some cases positive) associations.

The specific content type matters more than the platform. Appearance-focused content: transformation posts, before/afters, body-focused lifestyle content, consistently produces worse body image outcomes regardless of whether it’s Instagram, TikTok, or elsewhere. Non-appearance content on the same platforms — skill-based, interest-based, educational, doesn’t produce the same effects.

For women, the luteal phase specifically is the highest-risk window for appearance-based comparison. Estrogen falling in the late luteal phase is associated with lower mood, lower self-esteem, and higher susceptibility to social comparison. This isn’t widely acknowledged in either the mental health or the social media research, but the mechanism; reduced serotonin support reducing mood stability in a phase when body image is already hormonally more fragile is consistent with everything we know about how estrogen and serotonin interact.

The information in this post is for educational and informational purposes only. None of the above constitutes medical advice. Always consult a qualified healthcare professional for personal health concerns.

Between Saturdays is a weekly research roundup from Simply Salvia. Four things from science and wellness worth knowing about. If someone sent this to you, you can subscribe here.

Detailed Readings

Scientists discover ancient neurons that control attention

Dietary Protein Distribution Positively Influences 24-h Muscle Protein Synthesis in Healthy Adults

Alzheimer’s breakthrough: Scientists restore two hours of sleep without clearing brain plaques

Passive scrolling, active comparing: how social media use behaviours shape happiness through social comparison

Part 1 ended with the evidence hierarchy, which established that CBT and resistance training have the strongest evidence, that magnesium and omega-3s have genuinely good supporting evidence, and that most of what’s being sold in the anxiety supplement space has weaker evidence than its marketing suggests.

Part 2 is the practical half: the specific biological mechanisms of the interventions that work, and how to build them into a routine that’s actually manageable.

Table of contents

4. Your Gut and Your Anxiety: The Connection Is More Direct Than You Think

5. The Sleep-Anxiety Loop, And How to Break It

6. The Nutrition Chapter: Specific Mechanisms, Not Vague Advice

7. The Cycle-Aware Anxiety Protocol

8. The Complete Practical Guide

   This Substack is reader-supported. To receive new posts and support my work, consider becoming a free or paid subscriber.

Read more

Caught My Eye…

GLP-1 Drugs Are Doing Something to Mood and Behaviour That Nobody Fully Predicted

The GLP-1 receptor agonist story keeps getting more interesting. Semaglutide (Ozempic/Wegovy), tirzepatide, and similar drugs were developed for type 2 diabetes and obesity. The cardiometabolic evidence has been robust since their initial trials. What’s been emerging over the past 18 months, and was significantly reinforced in the first half of 2026, is a psychiatric dimension that wasn’t fully anticipated.

A large study found major drops in depression, anxiety, and psychiatric-related events in people taking GLP-1 medications like semaglutide. This follows a pattern that’s been building for a while: the GLP-1 receptor is present in the brain, not just in the gut and pancreas. GLP-1 agonists appear to act on the brain’s reward system thus reducing the reinforcing quality of addictive substances and behaviours.

A Rutgers study published in June 2026 found that GLP-1 drugs may weaken the link between impulsive tendencies and violent behaviour. A finding the researchers described as suggesting these medications affect decision-making and impulse regulation through the brain’s GLP-1 pathways. Separate research has found associations between GLP-1 medication use and reduced alcohol consumption, reduced gambling behaviour, and reduced drug cravings.

The honest framing: most of this research is observational or small-scale, and the psychiatric effects of GLP-1 agonists are not yet well enough understood to be the basis for prescribing them for mental health indications. The mechanism is plausible, GLP-1 receptors in the brain regulate reward pathways but the dose-response relationships, the duration of effect, and the implications for different psychiatric populations are still being worked out. The FDA has not approved any GLP-1 drug for psychiatric use.

What’s worth knowing regardless: the drugs that started as diabetes medications and became weight loss medications may turn out to have a third significant clinical domain in psychiatry and the fact that GLP-1 receptors exist throughout the brain has been reshaping how researchers think about appetite, reward, impulsivity, and mood as genuinely interconnected rather than parallel systems. That reframing has implications beyond the medications themselves.

Women With Autism and ADHD Are Being Diagnosed Decades Late. And Perimenopause Is Often the Trigger

This finding is sitting at the intersection of several things Simply Salvia has covered; ADHD and hormones, perimenopause and cognitive changes, the ADHD-cycle connection and the 2026 research adds a specific new dimension that pulls them together.

New research states:

The specific perimenopause connection is this: researchers are increasingly exploring how ADHD and autism present differently in women, including the role of masking behaviours and hormonal fluctuations, and recent studies have shown that autistic people and ADHDers may be particularly vulnerable to difficulties during menopause. Doctors have found women seek assessment during perimenopause, when hormonal changes can disrupt coping strategies that previously helped them navigate daily life.

The mechanism is overlapping with what I covered in the ADHD post earlier this year: estrogen’s role in dopamine signalling means that estrogen withdrawal, in the premenstrual window, postpartum, and most significantly through perimenopause, can strip away the neurochemical scaffolding that was keeping symptoms manageable. For women who have developed highly effective compensatory strategies across decades (masking, over-preparation, rigid routines that maintain function at significant personal cost) the hormonal disruption of perimenopause removes the reserve capacity those strategies depend on.

What makes this particularly significant is the diagnostic implication: a woman in her 40s experiencing sudden cognitive difficulties, overwhelm, and difficulty coping is very likely to be told this is menopause, or anxiety, or depression and to receive treatment targeted at those presentations, rather than investigation of whether an underlying neurodivergent condition that’s been masked throughout her life is now becoming clinically apparent for the first time.

The practical note: if you, or a woman in your life, is experiencing a significant shift in cognitive functioning, overwhelm tolerance, or sensory sensitivity during perimenopause and particularly if there are retrospective elements of the picture that resemble ADHD or autism traits throughout life this is worth raising specifically rather than accepting a purely hormonal explanation.

A Bone Hormone Is Being Used for Back Pain And the Mechanism Is Completely Unexpected

This one is genuinely surprising and falls into the category of findings that only make sense when you look at the biology underneath them.

A new study suggests a widely used bone hormone could help relieve chronic back pain in an unexpected way. Instead of just strengthening bone, it appears to stop pain-sensing nerves from growing into damaged spinal areas.

The hormone in question is related to bone metabolism, specifically the hormone involved in regulating the process by which bone is remodelled and maintained throughout adult life. The finding is that beyond its skeletal role, this hormone appears to regulate the growth of nociceptive nerve fibres (the nerves that carry pain signals) into damaged tissue. In the animal models tested, administering the hormone prevented pain-sensing nerves from innervating (growing into) damaged spinal disc tissue, which is one of the mechanisms by which chronic back pain becomes persistent and self-reinforcing.

This matters because chronic back pain is one of the leading causes of disability globally, and the treatment options beyond pain management are limited. Understanding the nerve-growth mechanism opens a conceptually different treatment pathway — one that targets the biological process that makes pain persist, rather than blocking pain signals after they’re already being generated.

The connection to women’s health specifically: bone hormones and bone turnover are more clinically significant in women than in men due to the accelerated bone loss that follows estrogen withdrawal at menopause. Women who are already being monitored for bone health markers may eventually be in a position where those same markers are relevant to pain management, a convergence between two health domains that currently have almost no overlap in clinical practice.

The Deep Sleep Circuit That Builds Muscle, Burns Fat, and Regulates Mood. Now Fully Mapped

In July 2026, a research team published the most complete picture yet of the brain circuitry that links deep sleep with growth hormone release confirming and extending the UC Berkeley finding.

Researchers have identified the brain circuitry that links deep sleep with the release of growth hormone, revealing how the two regulate each other.

This finding pulls together several threads that Simply Salvia has covered across multiple posts: the UC Berkeley sleep-GH research, the weight loss short dive’s discussion of why sleep deprivation impairs body composition, and the hair loss short dive’s note about GH’s role in follicle repair and cell division. What the new mapping adds is the specific neural circuitry; the exact brain regions and signalling pathways that control the deep sleep to GH release cascade, which is the foundation needed for any targeted intervention.

The clearest practical translation: the chain from deep sleep to physical recovery is now mapped well enough that we can say with confidence it goes: non-REM slow-wave sleep → hypothalamic circuit activation → growth hormone surge → muscle repair, fat metabolism regulation, bone maintenance, follicle cell division, and immune cell replenishment. Interrupting any part of this chain with alcohol, with elevated body temperature (the luteal phase mechanism), with early sleep cut-off, with chronic stress keeping cortisol elevated reduces the output at the end.

What’s worth sitting with: this isn’t a fringe claim in alternative wellness. The growth hormone regulation of adult tissue maintenance is fundamental physiology, it’s now mapped at the circuit level, and the implications span muscle composition, metabolic health, skin repair, hair growth, and immune function simultaneously. Sleep is not a passive state. It’s the maintenance window. And the circuitry that runs it is now visible enough to understand why every single intervention that disrupts deep sleep costs the body something real and measurable.

The information in this post is for educational and informational purposes only. None of the above constitutes medical advice. Always consult a qualified healthcare professional for personal health concerns.

Between Saturdays is a weekly research roundup from Simply Salvia. Four things from science and wellness worth knowing about. If someone sent this to you, you can subscribe here.

Detailed Readings

Weight loss drug Ozempic cuts depression, anxiety, and addiction risk

Researchers Link Use of GLP-1 Medications to Lower Risk of Violence

Gender Bias and Diagnostic Delays in Young Women: A Narrative Review

Scientists discover hormone that may stop chronic back pain at its source

Scientists discover the deep sleep circuit that builds muscle, burns fat, and boosts the brain

None of that is wrong. But it skips the part that would actually help most women understand what’s going on, which is why anxiety is happening in the first place, why it spikes at predictable points in the month, why it’s worse in certain years than others, and why the standard advice sometimes feels like it’s addressing a surface problem without touching what’s underneath it.

Women experience anxiety disorders at almost twice the rate of men. That gap appears in teenagers, in working women, in every age group and every country where researchers have looked. It is one of the most consistent findings in all of mental health research. And for most of the history of that research, the explanation was essentially “women are more anxious.” Not why. Just that they are.

The research has been getting considerably more specific since then. This short dive is the explanation.

1. Why Women Experience Anxiety at Almost Twice the Rate of Men

2. The Menstrual Cycle and Anxiety. The Most Specific Connection

3. The Evidence Hierarchy: What the Research Actually Ranks for Anxiety

Chapter 1: Why Women Experience Anxiety at Almost Twice the Rate of Men

The Headline Finding

Women are about twice as likely as men to experience major depression and significantly more likely to develop an anxiety disorder. The disparity holds steady whether you look at teenagers, working mothers, or women in midlife. This isn’t a cultural artefact or a matter of women being more willing to report symptoms, the gap persists across cultures, across healthcare systems, and in studies that control for reporting bias.

So what actually explains it?

The Hormonal Architecture

The clearest biological reason is one that’s been understood for years but rarely communicated clearly to the women it affects: estrogen and progesterone influence serotonin, dopamine, and GABA - the brain chemicals that regulate mood, fear, and emotional stability. When these hormones shift, so does a woman’s vulnerability to anxiety and low mood.

Let’s break that down into plain language, because those three brain chemicals matter in very specific ways:

Serotonin is the brain’s mood-stabilising system. It regulates fear responses, reduces the amygdala’s reactivity to threat, and is the primary target of SSRIs (the most commonly prescribed medications for anxiety and depression.) Falling estrogen pulls serotonin down with it, which is the direct biological mechanism behind the mood drop in the late luteal phase, after childbirth, and during perimenopause — all windows where estrogen declines sharply.

GABA is the brain’s main inhibitory neurotransmitter. It quiets neural activity and produces calm. It’s the system that benzodiazepines and alcohol work on, and it’s the system that progesterone’s metabolite (allopregnanolone) naturally activates throughout the luteal phase. More on this shortly, because this is where the anxiety-cycle connection gets very specific.

Dopamine regulates motivation, reward, and executive function, including the ability to redirect attention away from anxious thoughts. Estrogen supports dopamine signalling in the prefrontal cortex. As estrogen falls, dopamine’s regulatory effect on attention weakens, making it harder to break out of anxious thought loops.

These shifts are not constant; they spike during specific life stages. Puberty, the menstrual cycle, pregnancy, the postpartum period, and perimenopause each bring sharp hormonal change. This is why anxiety in women so often has a pattern, particular times of month, particular life chapters, that doesn’t fit neatly into the framing of anxiety as a fixed trait.

The Stress Response Is Wired Differently

Beyond hormones, there are structural differences in how women’s nervous systems process threat. The amygdala (the brain’s threat detection centre) responds to stress differently in women than in men. Research has found that under chronic stress, women are more likely to experience anxiety at an emotional and physiological level (heightened arousal, increased physical tension, persistent worry), while men tend to experience stress effects more cognitively (reduced focus, impaired decision-making). This isn’t a vulnerability in any moral sense, it’s a different threat-processing architecture, and it has consequences for which interventions actually work.

Women tend to be more prone to rumination when faced with stress, women are more likely to ruminate while men are more likely to actively seek solutions. Rumination isn’t a character trait. It’s partly a reflection of the serotonin-estrogen connection: higher serotonin supports the ability to interrupt anxious thought loops. When serotonin is lower (as it is at lower-estrogen points of the cycle), the brain’s capacity to disengage from threat-focused thinking is genuinely reduced.

The Inflammation Link

Women are more vulnerable to the effects of immune-inflammatory pathways, which increase the production of anxiety-inducing compounds. Chronic low-grade inflammation; the kind produced by ultra-processed diets, poor sleep, chronic stress, and gut dysbiosis activates these pathways more readily in women than in men, producing a neurological environment that’s more prone to anxiety and low mood.

This is part of why the gut-brain axis is so relevant to women’s anxiety specifically, and why the dietary and gut health interventions covered in Part 2 have a more direct mechanistic connection to anxiety in women than they do in men.

Chapter 2: The Menstrual Cycle and Anxiety. The Most Specific Connection

This is the chapter that will probably explain something you’ve lived for years without having a name for.

The GABA Story: Why the Week Before Your Period Is the Worst

Every month, in the second half of your cycle, progesterone rises after ovulation and its metabolite (a compound called allopregnanolone, I’ll just call it ALLO) binds to GABA-A receptors in the brain. This produces a mild sedative, calming effect that’s sometimes described as the brain’s built-in progesterone calmer. During the mid-luteal phase, when progesterone is high and ALLO levels are stable, many women notice they feel more settled, more tired (this is real — it’s ALLO), and generally more emotionally even.

Then comes the late luteal phase. Progesterone drops sharply in the days before menstruation begins. ALLO drops with it. And for many women, the brain’s response to losing that GABA support is what researchers now call a neurosteroid withdrawal, a rebound state characterised by heightened nervous system arousal, increased anxiety, difficulty sleeping, emotional reactivity, and the “wired but exhausted” feeling that most people know as PMS or PMDD.

Allopregnanolone, a positive allosteric modulator on the GABA-A receptor, is believed to be involved in the symptomatology of premenstrual dysphoric disorder, which is characterised by depression, irritability, mood swings and anxiety in the luteal phase of the menstrual cycle.

The research on PMDD specifically has become very clear on the mechanism: PMDD symptoms are linked to an altered sensitivity to normal luteal phase levels of allopregnanolone. Women with PMDD had lower expression of the delta subunit of the GABA-A receptor during the luteal phase, the exact point in the cycle when it should be going up. In plain language: their brain’s GABA system doesn’t adapt properly to the hormonal environment, so when ALLO is present, the calming effect isn’t registered and when ALLO withdraws, the nervous system rebounds more severely.

This mechanism isn’t exclusive to PMDD. It exists on a spectrum, PMDD is the severe end, but the milder version of the same pattern (more anxiety, worse sleep, more emotional reactivity in the late luteal phase) is experienced by a much larger proportion of women than the PMDD diagnosis captures.

Why This Means the Anxiety Isn’t the Same Every Week

The practical implication is one that most anxiety advice completely ignores: anxiety that’s driven by neurosteroid withdrawal in the late luteal phase is a different phenomenon from anxiety that’s driven by a chronic stressor, a diagnosed disorder, or a generalised pattern. It arrives at predictable points, it has a hormonal mechanism, and it responds to different interventions.

This is why two weeks of consistent meditation, magnesium supplementation, and good sleep can genuinely reduce anxiety and then the week before a period arrives and it feels like starting from scratch. The previous weeks’ interventions haven’t failed. A new, acute neurochemical event is happening on top of whatever baseline was being managed.

Tracking your anxiety levels across the cycle is one of the most useful diagnostic tools available, and it’s free. If anxiety reliably spikes in days 22–28 and improves within a day or two of your period starting, you have direct evidence of a luteal-phase anxiety pattern. That pattern responds to specific interventions (covered in Chapter 7 of Part 2) that aren’t the same as general anxiety management.

The Other Hormonal Windows

The luteal phase is the monthly version of this. But the same mechanism plays out at other hormonal transition points:

Postpartum: After birth, both estrogen and progesterone drop sharply. ALLO disappears with progesterone. The postpartum period is, neurochemically, the most dramatic GABA withdrawal a woman’s nervous system experiences in a lifetime, which is part of why postpartum anxiety and depression are so common and so severe. Brexanolone (a synthetic ALLO) has now been FDA-approved specifically for postpartum depression because of this mechanism.

Perimenopause: As estrogen declines erratically in the years before menopause, serotonin fluctuates with it. Many women describe a sudden-onset anxiety they’ve never experienced before, in their 40s, that doesn’t respond to the things that helped anxiety earlier in life. This is often the estrogen-serotonin connection manifesting at a new hormonal baseline — the brain chemistry has shifted, and the strategies built on an earlier hormonal environment are no longer as effective.

The Pill: Synthetic progestins in hormonal contraception affect the progesterone-ALLO pathway differently from natural progesterone and for some women, particularly those on formulations with higher androgenic progestins, this produces measurable effects on anxiety, mood, and emotional flatness. This is a documented side effect that’s been underreported and underdiscussed in the prescribing conversation.

Chapter 3: The Evidence Hierarchy: What the Research Actually Ranks for Anxiety

The Strongest Evidence

Cognitive behavioural therapy (CBT) sits at the top. A 2026 systematic review and network meta-analysis of exercise treatments for anxiety disorders found that resistance training showed the highest effectiveness compared with waitlist, closely followed by CBT. CBT has decades of clinical trial data, across multiple anxiety disorder types, in multiple populations. It works by changing the cognitive patterns that maintain anxiety, specifically, the interpretive biases and avoidance behaviours that keep the nervous system in a threat-detection state long after the original stressor has passed.

What CBT is not: a replacement for understanding the biological drivers. A woman with severe late-luteal anxiety who’s learned excellent CBT skills will still have the GABA withdrawal event every month. CBT gives her tools to navigate it; it doesn’t stop it happening. Understanding this prevents the extremely common experience of feeling like CBT has “failed” because anxiety returns cyclically, when actually the cycle itself is the variable that hasn’t been addressed.

Resistance training — resistance training showed the highest effectiveness of all exercise types for anxiety disorders in the 2026 meta-analysis, with an effect size (SMD −0.79) comparable to CBT. The mechanism: resistance training reduces inflammatory cytokines (specifically IL-6 and TNF-alpha), increases BDNF, and produces consistent hormonal changes including reduced cortisol reactivity over time. Two to three sessions per week of resistance training produces significant anxiety reduction at 8–12 weeks in clinical populations.

Aerobic exercise also has strong evidence; cardiovascular exercise raises BDNF, supports serotonin and dopamine synthesis, and reduces the physiological arousal that anxiety sustains. The dose that produces clinical benefit is lower than most people assume: 20–30 minutes of moderate-intensity aerobic exercise, three to four times per week, has consistent evidence for anxiety reduction.

What Has Good Supporting Evidence

Magnesium

It works on the GABA-A receptor. The same receptor system implicated in the luteal-phase anxiety mechanism. Low magnesium is associated with lower GABA-A sensitivity, more nervous system excitability, and worse anxiety. A systematic review of magnesium and anxiety found significant improvements in subjective anxiety with supplementation. The form matters: magnesium glycinate specifically has the best evidence for neurological effects. 300–400mg in the evening is the well-researched dose range.

Omega-3 fatty acids

They have a growing evidence base specifically for anxiety. A meta-analysis found significant reductions in anxiety symptoms with omega-3 supplementation in adults with clinical diagnoses. The mechanism: omega-3s reduce inflammatory cytokines that activate the anxiety-generating tryptophan catabolite pathways mentioned in Chapter 1. Women are more vulnerable to these pathways, which is part of why omega-3s may be specifically relevant to the female anxiety picture.

Sleep

Not as a passive recommendation but as a physiological intervention. Disrupted sleep elevates cortisol and reduces prefrontal cortex regulation of the amygdala, producing exactly the heightened threat-detection and reduced emotional regulation that anxiety consists of. Improving sleep quality is one of the most direct anxiety interventions available, and it’s not sufficiently emphasised in standard anxiety management advice.

What Has Weaker Evidence Than Its Marketing Suggests

Ashwagandha

It has some evidence for reducing self-reported stress and cortisol at doses of 300–600mg. The effect is real but modest, and the studies are often industry-funded and short-term. It’s a reasonable supportive addition to an anxiety management routine with good evidence foundations. It’s not a replacement for the above.

L-theanine

It shows some evidence for acute anxiety reduction in the hour following a dose. The effect is mild and short-lived. It’s found naturally in green tea at lower concentrations. Not harmful; not going to resolve underlying anxiety patterns.

CBD

The evidence is significantly weaker than the marketing implies for anxiety disorders specifically. Some studies show acute anxiolytic effects; the evidence for sustained anxiety reduction is thin. Quality control issues (many products contain different CBD concentrations than labelled) compound the picture.

Breathing exercises and mindfulness

Genuinely evidence-based, but often presented as primary interventions when their strongest evidence is as adjuncts alongside CBT or exercise. They work by activating the parasympathetic nervous system and interrupting the physiological arousal of the anxiety response. Valuable, particularly for acute anxiety management. Not sufficient on their own for anxiety that has biological drivers.

Part 1 ends here. Part 2 is where it becomes a practical framework. The gut-brain connection and what specific probiotic strains do for anxiety, the sleep-anxiety loop and how to break it, the nutrition chapter with specific mechanisms, the cycle-aware protocol for the weeks that are reliably hardest, and the complete guide to building a routine that actually works.

Now you understand what’s actually happening. Women experience anxiety at almost twice the rate of men because of a genuinely different hormonal architecture — estrogen and progesterone shaping serotonin, GABA, and dopamine in ways that make the nervous system more susceptible to specific kinds of disruption. You know the GABA-withdrawal mechanism that makes the week before your period the worst and why that’s a monthly neurochemical event, not a personal failing. And you have the honest evidence hierarchy for what the research actually supports.

Part 2 takes all of this further.

Chapter 4 is the gut-brain axis chapter. How the gut microbiome produces GABA and serotonin, what specific probiotic strains the 2026 research supports for anxiety, and why the gut-anxiety connection is specifically more relevant for women.

Chapter 5 is the sleep-anxiety loop. The specific mechanisms by which poor sleep drives anxiety and anxious nights drive poor sleep, and how to break in at each point.

Chapter 6 is the nutrition chapter. Magnesium in detail, omega-3s and their anti-inflammatory anxiety mechanism, blood sugar stability and cortisol, and what the Mediterranean diet research says specifically for anxiety.

Chapter 7 is the cycle-aware anxiety protocol. The specific, phase-by-phase interventions that address the luteal-phase pattern that general anxiety advice doesn’t touch.

Chapter 8 is the complete practical guide. How to build a routine that layers the evidence-backed interventions, what to do in different anxiety windows, and when the right answer is professional support rather than self-management.

Subscribe to read Part 2 →

Sources & Further Reading

Remes et al., Women are far more anxious than men — here’s the science — University of Cambridge / The Conversation

Women In Balance. Why women develop anxiety and depression at higher rates than men, June 2026

Farhane-Medina et al. Factors associated with gender and sex differences in anxiety prevalence and comorbidity: A systematic review — PMC, 2022

Bixo, Stiernman & Bäckström. Neurosteroids and premenstrual dysphoric disorder — British Journal of Psychiatry, July 2026

Samphire Neuroscience. Why normal hormones cause PMDD: the allopregnanolone theory explained, April 2026

Lei et al. Effectiveness and acceptability of exercise treatments for adults with anxiety disorders: systematic review and network meta-analysis — BMJ Open Sport & Exercise Medicine, January 2026

Boyle et al. The effects of magnesium supplementation on subjective anxiety and stress: a systematic review — Nutrients, 2017

EASe-GAD Trial. Dietary counselling plus omega-3 supplementation in the treatment of generalised anxiety disorder — Neuropsychiatric Disease and Treatment, 2024

PMC meta-analysis. Effects of prebiotics and probiotics on symptoms of depression and anxiety in clinically diagnosed samples, 2025

Frontiers in Microbiology. Psychobiotics in mental health: insights from human clinical trials via the gut-brain axis, March 2026

ScienceDaily. A daily probiotic may help relieve depression and anxiety, June 17, 2026

Caught My Eye…

Why Women Get IBS More Than Men: A Nobel Laureate Just Found the Answer

Two thirds of people with irritable bowel syndrome are women. This has been known for decades. Why it’s true has been, until very recently, a genuine medical mystery, which is another way of saying it hadn’t been studied seriously enough.

A study published in the journal Science in December 2025, led by researchers at UCSF, including co-senior author David Julius, who won the 2021 Nobel Prize for his work on pain sensation found the mechanism. It’s estrogen. But not in the way you might assume.

The researchers expected to find estrogen receptors on a specific type of gut cell called enterochromaffin (EC) cells, which are known to signal pain from the gut to the spinal cord. Instead they found something unexpected: the estrogen receptors were clustered on a different, rarer cell type called L-cells in the lower colon. When estrogen binds to these L-cells, it triggers them to release a hormone called PYY (peptide YY). PYY then acts on neighbouring EC cells, causing them to pump out serotonin which activates the pain-sensing nerve fibres that signal to the brain.

When male mice were given estrogen to mimic the levels found in females, their gut pain sensitivity increased to match that of females. The mechanism isn’t just female anatomy, it’s female hormones actively turning up the gut’s pain sensitivity dial.

There’s a second layer that makes this even more interesting. Estrogen didn’t just increase baseline PYY release, it also caused L-cells to produce more receptors for short-chain fatty acids, the metabolites produced when gut bacteria break down certain fermentable foods. This means estrogen creates what the researchers called a “double hit”: it raises baseline gut pain sensitivity, and simultaneously makes L-cells more reactive to food-derived compounds in the colon.

This directly explains two things that have long puzzled IBS research. First, why low-FODMAP diets, which eliminate fermentable carbohydrates like onions, garlic, wheat, beans, and honey, help a significant subset of IBS patients: those foods produce the short-chain fatty acids that trigger the newly sensitised L-cells. Second, why women’s gut symptoms often fluctuate with their menstrual cycles, the estrogen-PYY-serotonin pathway would be more active at higher-estrogen points in the cycle, specifically around ovulation and in the follicular phase when estrogen peaks.

There’s also a retrospective clarity this finding brings to a long-standing pharmaceutical puzzle. For decades, PYY was understood primarily as an appetite-suppressing hormone, drug companies tried developing it as a weight-loss medication. Those trials were abandoned after participants reported severe gut distress. The new findings explain what was previously a mystery: PYY wasn’t just suppressing appetite, it was activating a gut pain pathway that nobody had mapped yet.

The practical takeaway for anyone managing IBS or chronic gut symptoms: cycle tracking alongside food and symptom diaries is worth doing, because the hormonal fluctuation affecting gut sensitivity is now mechanistically confirmed rather than anecdotally noted. Symptoms that are worse in specific weeks of the month aren’t random or psychological, they’re estrogen acting on a pathway that is now thoroughly described in the research.

Probiotics and Depression: The June 2026 Trial and What the Broader Evidence Now Says

A clinical trial published in the Journal of the American Geriatrics Society on June 17, 2026 found that daily probiotic supplementation, when added to standard antidepressant treatment, produced modest but meaningful improvements in depression and anxiety symptoms over 12 weeks, compared to placebo plus antidepressant alone. The trial also measured serum BDNF (brain-derived neurotrophic factor) a marker of brain plasticity and mood health and found meaningful differences between the groups.

This builds on a comprehensive scientific analysis covering over 1,400 clinically diagnosed patients that found probiotics are a potent tool against depression and anxiety.

But rather than treating this single trial in isolation, it’s worth contextualising it within the broader picture that’s been assembling in 2026:

A systematic review and meta-analysis published this year, covering RCTs of probiotic and prebiotic interventions in clinically diagnosed depression and anxiety patients, concluded: probiotics showed substantial reductions in depression symptoms and moderate reductions in anxiety symptoms. Up to 8 weeks of probiotic use compared with placebo was effective in reducing depressive and anxiety symptoms in clinically diagnosed patients.

A Frontiers in Microbiology review from March 2026 highlighted the gut-brain axis as a critical modulator of mental health, positioning specific probiotic strains — Lactobacillus rhamnosus, Bifidobacterium longum, and Lactobacillus gasseri specifically, as promising interventions for anxiety, stress, depression, and cognitive function.

The mechanism makes sense of this: the gut microbiome produces approximately 90-95% of the body’s serotonin and substantial amounts of GABA. It communicates with the brain via the vagus nerve and through circulating inflammatory cytokines. When gut composition is disrupted, these neurotransmitter and anti-inflammatory pathways are impaired at the source. Restoring gut diversity whether through diet, prebiotics, or specific probiotic strains can restore some of what’s been lost.

Two important caveats worth holding: the effects are currently most consistently demonstrated as an adjunct to existing treatment rather than a standalone replacement for it. And the specific strain matters enormously “probiotics” as a category cover hundreds of different bacterial strains with different mechanisms, and not all of them have the same effect. The consistent findings cluster around specific Lactobacillus and Bifidobacterium strains at adequate doses, not random probiotic supplements.

The practical framing: for anyone managing low mood or anxiety and already interested in gut health from a general wellbeing perspective, the evidence for specific probiotic strains as a supportive addition to broader treatment is now considerably stronger than it was two years ago. It isn’t a replacement for therapy or medication. It’s a genuinely evidence-informed complementary intervention.

The Estrobolome, Gut Bacteria, and Menopausal Health. A Major Review Just Connected the Dots

I’ve covered the estrobolome (the collection of gut bacteria responsible for metabolising estrogen) in previous editions focused on younger women and hormonal acne. A major review published in April 2026 in PMC now pulls together a comprehensive picture of how the estrobolome intersects with menopausal health specifically, and the findings are significant enough to stand alone.

This review synthesises current understanding of the bidirectional relationship between estrogen and the gut microbiome and its implications for women’s health during menopause including cardiometabolic, musculoskeletal, and urogenital disorders.

The core relationship: when gut microbiome diversity is high, estrogen is metabolised and cleared from the body efficiently. When diversity is low driven by poor diet, antibiotic use, chronic stress, or poor sleep, an enzyme called beta-glucuronidase becomes overactive, and oestrogen that should be excreted gets reabsorbed back into the bloodstream. This creates a state of impaired estrogen clearance that has different implications across different phases of a woman’s life.

In the menopausal transition, where estrogen is already declining, poor estrobolome function can amplify the hormonal instability of perimenopause, making the fluctuations more extreme, worsening the symptoms of both estrogen highs and estrogen lows that characterise this transition. The review found consistent associations between gut microbiome composition and several menopausal health markers: bone density, cardiovascular risk, mood and cognitive symptoms, and vaginal health.

What this adds to the menopausal conversation that’s been running across previous editions: the gut microbiome is not only relevant to younger women managing acne and cycle symptoms. It’s a significant and modifiable variable in menopausal health outcomes, one that sits outside the HRT conversation but may complement it. The dietary pattern that most consistently supports a healthy estrobolome (high-fibre, fermented foods, reduced ultra-processed food) is a longitudinal investment, not a perimenopausal intervention. Starting now, regardless of where you are in your hormonal timeline, is more useful than starting at the point when symptoms arrive.

The Shingles Vaccine Finding That Isn’t Just About Shingles

A new study found that a shingles vaccine cut major cardiac events by 46% and deaths by an impressive 66% within a year in people already at high risk.

The shingles vaccine (Shingrix) was developed to prevent varicella-zoster virus reactivation. Its mechanism is immunological (it primes the immune system against a specific pathogen). The finding that it also reduces cardiac events and mortality by these magnitudes in high-risk populations points to something more systemic: the chronic, low-grade inflammation produced by latent viral infections (herpes viruses, including varicella-zoster, stay in the nervous system after the initial infection) may be a driver of cardiovascular disease that’s largely been overlooked in standard cardiac risk assessment.

This fits a growing body of research connecting chronic viral burden, the accumulated latent infections your immune system is managing at any given time, with systemic inflammation and cardiovascular risk. Cytomegalovirus, Epstein-Barr virus (the one that causes mono), and herpes simplex are all under active investigation as contributors to atherosclerosis and cardiovascular events through the same inflammatory pathway.

The practical note: shingles vaccination is typically recommended from age 50 in most countries. For older family members who haven’t had it particularly those with existing cardiac risk factors, this trial result adds a meaningful additional argument for it beyond shingles prevention. And more broadly: the connection between immune burden, latent viral infections, and cardiovascular health is an area where the research is accumulating faster than the clinical guidelines are updating.

The information in this post is for educational and informational purposes only. None of the above constitutes medical advice. Always consult a qualified healthcare professional for personal health concerns.

Between Saturdays is a weekly research roundup from Simply Salvia. Four things from science and wellness worth knowing about. If someone sent this to you, you can subscribe here.

Detailed Readings

A Cellular Basis for Heightened Gut Sensitivity in Females

Toward Hormone-Aware Pain Treatments: Estrogen, Diet, and the Biology of IBS

A daily probiotic may help relieve depression and anxiety

Psychobiotics in mental health: insights from human clinical trials via the gut-brain axis

Diet, the Gut Microbiome, and Estrogen Physiology: A Review in Menopausal Health and Interventions

This common vaccine cuts heart risk nearly in half in new study

Part 1 ended on the mineral-versus-chemical question, which is the debate most sunscreen content spends all its energy on. Part 2 is about the things that matter just as much and get almost no attention: how much you’re actually applying, whether your protection routine is quietly making you vitamin D deficient, what to do if your skin doesn’t tolerate standard formulas well, and the hormonal layer of pigmentation that no amount of perfect SPF technique alone will fully solve.

Table of Contents

4. How Much to Actually Apply. The Gap Is Bigger Than You Think

5. The Vitamin D Balance: Protecting Skin Without Becoming Deficient

6. SPF for Acne-Prone, Sensitive, and Reactive Skin

7. The Hormonal Pigmentation Connection: Melasma and Your Cycle

8. The Complete Practical Guide

9. Conclusion: The Habit That Outperforms Almost Everything Else in Skincare

Read more

Caught My Eye…

Women Are Becoming the Most Informed, Most Demanding Patients in Healthcare History. And the Data Backs It Up

This is a genuinely significant cultural and clinical shift, and it’s happening faster than most healthcare systems are adapting to it.

A 2026 trends report combining surveys of 105 healthcare professionals and 2,000 women, plus global research, found that women’s health is at a cultural and scientific turning point. The core finding: women are no longer passive patients. They’re informed, engaged, and actively reshaping the healthcare system from the patient side, researching their own symptoms, requesting specific tests, pushing back on dismissive explanations, and increasingly using wearables and at-home testing to generate their own longitudinal health data rather than waiting for a system that has historically taken years to investigate their symptoms properly.

This shift is being driven by a few converging forces. Information access has fundamentally changed, research that used to live exclusively in academic journals is now reaching women directly, including through publications like this one. Wearable and at-home testing technology has made it possible to track cycle data, sleep, heart rate variability, and hormone levels without needing a referral. And a growing public awareness of the historical research gap in women’s health, the fact that so much foundational medical research was conducted primarily on men and only recently is being properly studied across sexes has shifted from a niche advocacy topic to mainstream awareness.

The report also points to digital phenotyping, analysing patterns in activity, sleep, and stress data as able to identify risk for depression and anxiety with up to 85% accuracy before clinical onset, suggesting that personal health data is moving from a passive tracking exercise into genuinely predictive territory.

What this means practically: the dynamic between patient and doctor is shifting, and bringing specific information, specific test requests, and tracked personal data into an appointment is increasingly normal and increasingly effective, not pushy or excessive. If anything, the research suggests healthcare systems are still catching up to how informed and engaged the average woman patient already is.

Women’s Brain Health Has Been a $250 Billion Research Gap. That’s Finally Starting to Close.

This is one of the more concrete signals of where research investment is heading, and it connects directly to several findings I’ve covered recently: the menopause and grey matter research, the ADHD and hormones research, the perimenopause cognitive symptom research.

Women’s brain health is estimated as a $250 billion research and investment opportunity, representing 26% of the broader $1 trillion gap in women’s health research funding generally. For most of medical research history, brain health research has been conducted predominantly in male subjects or male animal models, with female-specific hormonal influences on cognition, mood, and neurological ageing treated as a confounding variable to control for rather than a primary area of study.

That’s beginning to shift substantially. 2026 is expected to bring the first explicitly women’s brain health research initiatives, dedicated funding programmes, acceleration programmes, and corporate investment specifically connecting midlife hormonal care with long-term cognitive outcomes. Growing evidence linking menopause, cardiovascular risk, autoimmune disease, and neurodegeneration is bringing dedicated attention back to women’s brain health as its own research domain, rather than a subset of general neurology.

Wearables and digital health platforms are expected to play a significant role here too, generating the longitudinal datasets on sleep, mood, cognition, and vasomotor symptoms across years that have simply never existed before, providing the foundation for entirely new categories of intervention that haven’t been possible without that data.

This matters because so much of what’s currently understood about hormones and cognition; the menopause brain fog, the ADHD-cycle connection, the anxiety that intensifies during hormonal transitions has been pieced together from a relatively small and recent body of research. A dedicated, well-funded research domain specifically for women’s brain health means the next five to ten years are likely to produce substantially more clarity on questions that currently still have more nuance than certainty.

Midlife Women’s Health Is Finally Being Treated as a Medical Priority, Not “Just Getting Older”

This connects to several threads I’ve covered; the HRT black box warning removal, the menopause and brain research but the bigger picture is worth naming directly, because it explains why so much menopause-related research has been surfacing recently.

International health leaders predict that by 2026, menopause will be treated as a serious medical and longevity inflection point, rather than merely a lifestyle inconvenience. Clinical organisations are expanding training programmes specifically to equip physicians with evidence-based menopause treatment strategies, including hormone therapy, broader symptom management, and long-term risk assessment, areas where, until recently, many GPs received minimal dedicated training.

The scale of the historical gap is significant. Menopause symptoms significantly disrupt daily functioning for most women who experience them, yet more than 80% never seek care, a statistic reflecting decades of under-recognition rather than a lack of need. Menopause is associated with systemic physiological changes affecting sleep, emotional stability, bone density, metabolism, and cardiovascular risk meaning the consequences of inadequate care during this transition extend well beyond the most commonly discussed symptoms like hot flushes.

For anyone in their 20s or early 30s reading this: this matters earlier than it might seem. The structural changes happening in research funding and clinical training now are shaping what kind of care will be available when you reach perimenopause and understanding that this transition is increasingly recognised as a major health inflection point, not a symptom set to quietly endure, is useful information well before you’re the one experiencing it. It’s also useful for advocating for mothers, aunts, and older colleagues navigating it right now within a system that’s still catching up.

Endometriosis Research Funding and Diagnostic Innovation Are Accelerating Together. Here’s Why That Combination Matters

This is a direct follow-up to the endometriosis research covered earlier this month, and the funding and innovation picture adds useful context to why the diagnostic landscape may finally be shifting after decades of stagnation.

The core problem with endometriosis diagnosis has never really been a lack of medical interest in solving it, it’s been the combination of no reliable non-invasive biomarker and a historical tendency to treat severe period pain as a normal, if unfortunate, part of being a woman, which delayed research investment for decades. Research is now exploring new diagnostic approaches using menstrual blood, saliva, and technologies including High-Intensity Focused Ultrasound, multiple parallel approaches to solving the non-invasive diagnosis problem simultaneously, rather than the single, slow-moving research line that characterised previous decades.

STAT News coverage of new clinical guidance noted something important: if endometriosis continues to be understood narrowly as a gynaecological disorder rather than a systemic inflammatory condition with effects throughout the body, diagnostic delay will persist regardless of how good the new guidance or diagnostic tools become. In other words: the technology and the funding are necessary but not sufficient. The conceptual shift; treating endometriosis as a whole-body inflammatory disease rather than “a bad period” has to happen alongside the diagnostic innovation, or the new tools will simply confirm diagnoses years later than they should, rather than catching the condition early.

The same coverage made the cost of delay explicit: during the years between symptom onset and diagnosis, inflammation progresses, adhesions form, ovarian tissue is distorted, fertility windows narrow, school days are missed, and careers quietly adjust around pain that patients eventually begin to reinterpret as a normal part of their biology. That reinterpretation, coming to believe that debilitating pain is simply normal, is itself one of the most damaging consequences of prolonged diagnostic delay, because it teaches people to stop advocating for themselves.

The practical takeaway, again: period pain that disrupts daily function is not something to quietly absorb as normal while waiting for research and diagnostics to eventually catch up. The system is improving. It isn’t there yet. Self-advocacy in the meantime remains the most reliable tool available.

The information in this post is for educational and informational purposes only. None of the above constitutes medical advice. Always consult a qualified healthcare professional for personal health concerns.

Between Saturdays is a weekly research roundup from Simply Salvia. Four things from science and wellness worth knowing about. If someone sent this to you, you can subscribe here.

Detailed Readings

Mira’s health report: 6 trends reshaping 2026

Women's health: Predictions for 2026

In 2026, Women’s Health Research Will Finally Focus on Midlife

Endometriosis is not just a gynecological disease

That’s not a knock on anyone’s intelligence. It’s a knock on where the information has been coming from. The same survey found that 36% of Gen Z say influencers are their primary source of skincare information and a lot of what’s circulating is confidently wrong. A tan being a sign of “healthy” skin. SPF only mattering on sunny days. A higher SPF number meaning you can apply less. These aren’t fringe beliefs. They’re common enough to show up in a national survey.

Meanwhile, “skin longevity” has become the defining skincare conversation of 2026, the shift from fixing damage after it happens to keeping skin functioning well for decades. Which makes this the perfect, slightly ironic moment to point out: the single most powerful skin longevity tool already exists, it’s been sitting in your bathroom cabinet the whole time, and most people are using it wrong or not using it enough.

This short dive is the sunscreen guide that should have existed years ago. What UV radiation is actually doing to your skin at a cellular level. Which myths are costing you the most. The honest, current state of the mineral-versus-chemical debate, including a few 2026 developments that haven’t filtered into mainstream skincare content yet. And in Part 2, the practical guide: how much to actually use, the vitamin D balance, and what to do if your skin is acne-prone, sensitive, or prone to pigmentation.

Let’s start with the biology.

1. What UV Radiation Actually Does to Your Skin

2. The Myths Costing You the Most

3. Mineral vs. Chemical Filters. What the Evidence Actually Says in 2026

Chapter 1: What UV Radiation Actually Does to Your Skin

Two Types of Rays, Two Different Kinds of Damage

Sunlight that reaches your skin contains two types of ultraviolet radiation that matter for skin health: UVA and UVB. They’re often talked about as if they’re interchangeable. They’re not. They damage skin through different mechanisms, at different depths, with different consequences and understanding the difference is the foundation for understanding why SPF alone isn’t the whole story.

UVB is the shorter-wavelength ray. It mostly affects the outer layer of your skin (the epidermis). This is the ray responsible for sunburn, and it works by directly damaging your skin cells’ DNA. When UVB hits a skin cell, it causes specific kinds of DNA damage where the building blocks of your DNA fuse together incorrectly. Your body has repair systems for this kind of damage, but they’re not perfect and the damage that doesn’t get repaired correctly is the kind that’s strongly linked to skin cancer development over time.

UVA is the longer-wavelength ray, and it penetrates much deeper, all the way into the dermis, the layer of skin where collagen and elastin live. This is the layer responsible for your skin’s structure, firmness, and bounce. UVA’s main damage pathway isn’t direct DNA breakage. It’s oxidative stress: UVA exposure generates reactive oxygen species inside skin cells, which then activate enzymes called MMPs (matrix metalloproteinases) that actively break down collagen. Research comparing UVA and UVB damage at the cellular level found that UVA specifically promotes the breakdown of dermal collagen fibres and triggers inflammation, while UVB primarily affects the surface cells. UVA penetrates roughly 1.6 times deeper into skin than UVB, which is exactly why it’s the ray most responsible for wrinkles, sagging, and loss of elasticity, while UVB is more associated with burning and surface damage.

Here’s the part that matters most: UVA is present at consistent intensity all day, every day, all year round, including through clouds and through glass windows. UVB intensity varies much more by time of day and season. This is why “I’m not getting sun damage, it’s cloudy” or “I’m inside all day” are two of the most common and most costly misunderstandings about sun protection. The ray responsible for collagen breakdown doesn’t care whether you can feel the heat.

Why the Damage Is Invisible Until It Isn’t

This is the part of “skin longevity” content that often gets skipped: by the time photoageing is visible; fine lines, uneven texture, brown spots, looser skin, the damage has usually been accumulating for years, sometimes decades.

The collagen breakdown triggered by UVA exposure happens immediately at a cellular level, every time skin is exposed without protection. But collagen is abundant, and the visible effects of its breakdown only become apparent once a critical threshold has been crossed. Research using collagen gels found that UVA radiation specifically causes hardening and loss of elasticity in collagen, more so than UVB and that this effect compounds with cumulative exposure over time. This is why someone who’s 24 and never worn SPF consistently doesn’t look damaged yet, but the cellular process that produces visible photoageing at 35 or 40 has already been running for years.

This delay between cause and visible effect is precisely why prevention has to start before there’s anything to see. It’s the same logic that applies to bone density, as covered in a previous Between Saturdays; peak collagen density and skin structural integrity are being built and maintained right now, in your teens, 20s, and early 30s, whether or not you’re paying attention to it.

The DNA Damage Layer: Why This Isn’t Just About Wrinkles

It’s worth being direct about the more serious side of this conversation, because most skincare content focused on “skin longevity” and ageing tends to underplay it.

UVB radiation directly forms specific DNA lesions; cyclobutane pyrimidine dimers and related photoproducts, that are strongly associated with skin cancer development when they aren’t correctly repaired. UVA contributes too, primarily through oxidative DNA damage, and has its own documented association with melanoma risk. The cumulative, unprotected exposure that produces visible photoageing over years is the same cumulative exposure that raises skin cancer risk over the same period.

Even mild psychological stress appears to amplify UV damage at the cellular level. A 2024 study found that stress occurring during UVB exposure degraded collagen function by suppressing its production, compounding the damage already happening from the UV exposure itself. This is a genuinely interesting finding: the stress-skin connection covered in earlier Simply Salvia content isn’t separate from sun damage, it appears to interact with it directly.

None of this is meant to be alarming for its own sake. It’s meant to explain why “I’ll start caring about sunscreen when I’m older” is backwards. The damage that shows up later is being determined now.

Chapter 2: The Myths Costing You the Most

This is the chapter built directly around the specific gaps the 2026 AAD survey identified, the beliefs that are common, confidently held, and wrong.

“A Tan Means Healthy Skin”

This is the single most damaging misconception in the survey results, and it’s worth being completely clear about: there is no such thing as a healthy tan. Any visible tan is a sign of UV damage that has already occurred, it’s your skin’s melanin-producing cells responding to DNA damage by producing more pigment as a protective (and imperfect) response. A tan is your skin’s distress signal, not a sign of vitality.

This doesn’t mean sunlight itself is the enemy, sensible sun exposure has real benefits, covered in Chapter 5 of Part 2. It means that the specific outcome of “getting a tan” visible skin darkening from UV exposure is, by definition, evidence of damage having occurred, not a wellness goal to pursue.

“SPF Is Only Necessary on Sunny Days”

UV radiation, particularly UVA, isn’t meaningfully reduced by cloud cover. Up to 80% of UV rays can penetrate cloud cover, meaning a grey, overcast day can deliver nearly as much UVA exposure as a clear one. This is one of the more counterintuitive facts in sun safety, because cloud cover reduces the heat you feel, which intuitively (and wrongly) reads as reduced UV exposure.

The practical implication: daily SPF isn’t a summer habit or a beach-day habit. It’s a daily habit, regardless of forecast, because the ray most responsible for long-term collagen damage doesn’t fluctuate with visible weather conditions.

“Higher SPF Means I Can Apply Less”

This is backwards, and it’s a genuinely costly misunderstanding. SPF protection doesn’t scale linearly with the number, it scales logarithmically, and crucially, the SPF rating on any bottle is only achieved at a specific application amount (2mg per cm² of skin, which works out to roughly a nickel-sized amount for the face). Most people apply somewhere between a quarter and half of this amount in real-world use, which means an SPF 50 product applied at half the recommended amount delivers closer to SPF 10–15, not SPF 25.

A higher SPF number gives you more margin for under-application, not permission to under-apply. The number on the bottle is a ceiling you only reach with the correct amount.

“My Foundation/Moisturiser Has SPF, So I’m Covered”

Multi-purpose products with SPF built in are genuinely useful as a layer of protection, but they’re rarely sufficient as the only layer, for two reasons. First, people apply far less foundation or tinted moisturiser to their face than the amount needed to achieve the labelled SPF, typically a fraction of a nickel-sized amount, when full SPF protection requires significantly more. Second, many of these products aren’t reapplied through the day the way a dedicated sunscreen would be, even though SPF protection degrades with time and UV exposure regardless of the product format.

The practical guidance dermatologists give consistently: treat SPF-containing makeup as a bonus layer on top of a dedicated sunscreen applied properly underneath, not as a replacement for one.

“Sunscreen Causes More Harm Than the Sun Itself”

This belief has gained traction from genuine, evolving research on chemical sunscreen absorption, covered honestly in Chapter 3 but it’s frequently overstated into “sunscreen is dangerous,” which isn’t what the evidence supports. The honest research distinguishes between specific chemical filters with documented absorption and hormonal interaction concerns, and the category of sunscreen as a whole, which has decades of evidence supporting its role in reducing photoageing and skin cancer risk. The next chapter goes into this distinction properly.

Chapter 3: Mineral vs. Chemical Filters. What the Evidence Actually Says in 2026

This is the part of the sunscreen conversation that’s evolved the most recently, and it deserves a more current and more nuanced treatment than most existing content gives it.

How Each Type Works

Mineral (physical) sunscreens use zinc oxide and/or titanium dioxide. These work primarily by sitting on the skin’s surface and physically reflecting and scattering UV radiation, rather than absorbing it into the skin. Studies using isotopically labelled zinc oxide have found minimal systemic absorption through intact human skin meaning very little of it enters the bloodstream. Zinc oxide also has independent anti-inflammatory and barrier-supportive properties, which is part of why it’s frequently recommended for sensitive or reactive skin.

Chemical (organic) sunscreens use compounds like oxybenzone, octinoxate, octocrylene, homosalate, octisalate, and avobenzone. These work by absorbing UV radiation and converting it to heat, which is then released from the skin. They tend to feel lighter, blend more easily, and are less likely to leave a visible cast, which has historically made them the more popular choice, particularly on deeper skin tones.

The Absorption Question: What 2026 Research Actually Shows

This is where the conversation has shifted meaningfully in the past few years, and it’s worth being precise rather than alarmist.

A 2019 FDA study found that several common chemical UV filters like oxybenzone, avobenzone, octocrylene, and others were absorbed into the bloodstream at levels significantly higher than previously understood, in some cases far exceeding the FDA’s own threshold for requiring further safety testing. A 2020 JAMA study found that a single day of using an oxybenzone-containing lotion produced plasma concentrations of 94.2 ng/mL, nearly 200 times the FDA’s 0.5 ng/mL threshold below which further testing typically isn’t required.

The important nuance: exceeding that threshold means the FDA wants more data, it does not automatically mean harm has been demonstrated. But the specific concern with oxybenzone has accumulated more weight over time. One fertility clinic cohort study found that higher oxybenzone levels were associated with lower antral follicle count in women under 35, and higher FSH (a hormone marker of declining ovarian reserve) in women over 35 suggesting a possible hormonal effect, though human research in this area remains limited and the clinical significance isn’t fully established. The National Toxicology Program also released findings linking oxybenzone exposure to increased thyroid tumour risk in female rats, and the European Commission’s safety review concluded oxybenzone is not considered safe at current permitted concentrations.

This research has had a real, measurable effect on the market: oxybenzone appeared in 70% of chemical sunscreens tested in 2016, and by 2026 that figure had dropped to just 5%, the industry has been actively reformulating away from it in response to the accumulating evidence, even ahead of any formal ban.

What This Means Practically, Without the Panic

The honest takeaway isn’t “chemical sunscreen is dangerous, switch to mineral immediately.” It’s more specific than that:

The strongest concern is specifically tied to oxybenzone, not chemical sunscreens as a category. If you check your sunscreen’s ingredient list and oxybenzone (sometimes listed as benzophenone-3 or BP-3) isn’t there, the absorption and hormonal concerns from the research above largely don’t apply to your product.

Some newer and more widely used in Europe chemical filters, bemotrizinol in particular have significantly better safety profiles, with minimal systemic absorption and no documented hormonal disruption concerns, and have been used safely across Europe, Asia, and Australia for over 20 years. The FDA approved bemotrizinol for use in the US for the first time in over two decades, with products expected to reach shelves in late 2026, a meaningful regulatory shift that’s been a long time coming.

Mineral sunscreen remains the most conservative choice for anyone wanting to minimise systemic absorption with the most established safety data, and is generally the first recommendation for sensitive skin, pregnancy, and younger users. The trade-off is cosmetic: mineral formulas can leave more of a visible cast, particularly on deeper skin tones, although tinted mineral formulas have improved significantly.

What’s not well supported by the evidence: avoiding sunscreen altogether because of these concerns. The documented risks of unprotected UV exposure; collagen breakdown, DNA damage, skin cancer risk are considerably better established and more serious than the absorption concerns around specific chemical filters. The right response to the oxybenzone research is switching to mineral sunscreen or a chemical sunscreen without oxybenzone, not abandoning sun protection.

Part 1 ends here. Part 2 covers exactly how much sunscreen to actually apply (the real-world gap is bigger than most people realise), how to balance sun protection with vitamin D, what to do if you’re acne-prone or dealing with pigmentation, the specific hormonal connection to melasma that almost no one explains properly, and the complete practical guide with product recommendations at every price point.

Now you understand what UV radiation is actually doing to your skin. The difference between UVA’s deep collagen damage and UVB’s surface-level burning and DNA damage, and why the visible effects show up years after the cellular damage begins. You know which myths are costing the most: the tan myth, the cloudy-day myth, the “higher SPF means less product” myth. And you have the current, nuanced picture on mineral versus chemical filters including the oxybenzone research specifically, rather than a blanket judgement on an entire category.

Part 2 turns all of this into something you can actually use.

Chapter 4 covers exactly how much sunscreen to apply and how often, including the research on just how large the real-world gap is between the SPF on the label and the protection most people are actually getting.

Chapter 5 is the vitamin D chapter. How to protect your skin without ending up deficient, and what the evidence actually supports as a reasonable middle ground.

Chapter 6 is specific to acne-prone, sensitive, and reactive skin, which formulas tend to work best and which ingredients to watch for.

Chapter 7 covers the hormonal dimension of sun damage that almost nobody explains properly: melasma, the menstrual cycle, and why pigmentation can worsen at specific hormonal points regardless of how diligent your SPF routine is.

Chapter 8 is the complete practical guide: product recommendations at every price point, the application cheat sheet, and the daily routine.

Subscribe to read Part 2 →

Sources & Further Reading

Comparison of the Biological Impact of UVA and UVB upon the Skin with Functional Proteomics and Immunohistochemistry — PMC

A comparative study of UVA and UVB radiation: Mechanisms of DNA damage and repair — Indonesia Journal of Biomedical Science

Analysis of UV Radiation Wavelengths Causing Hardening and Reduced Elasticity of Collagen Gels In Vitro — MDPI

Early stage UV irradiation damage to skin collagen suppressed by HPA axis control — ScienceDirect

Gen Z is most exposed to sunscreen misinformation on TikTok — EMARKETER, AAD survey data, January 2026

AAD: How to apply sunscreen — American Academy of Dermatology guidance

The Great Debate: Mineral vs Chemical Sunscreen — Dr. Heather Rogers, April 2026

What Sunscreen Is Safe? Mineral vs. Chemical Explained — ScienceInsights, April 2026

EWG’s Trouble with Sunscreen Chemicals report, 2026

EWG’s 20th Annual Guide to Sunscreens, May 2026

Targeting Melasma: Innovations in Pigment Deposition and Photoaging — Journal of Cosmetic Dermatology, January 2026

Mechanisms of Estrogen and Progesterone in Melasma — International Journal of Molecular Sciences, 2025

Dietary antioxidant intake in women with facial melasma — case-control study, October 2025

Caught My Eye…

Why You Get Sick Right After the Stressful Period Ends, Not During It

Most people have experienced this pattern: you push through a stretch of deadlines, exams, or a family crisis, holding it together the entire time and then the moment things calm down, you get sick. A cold, a flu, a flare of something chronic. It feels almost unfair. You made it through the hard part. Why now?

The immune research explains this precisely, and it comes down to a distinction between acute and chronic stress that’s worth understanding properly.

Acute stress; the short, intense kind actually enhances certain immune functions. It mobilises immune cells, increases inflammatory readiness, and prepares the body for potential injury or infection. This is the stress response working as designed: a short-term boost in defensive readiness, evolved for genuine physical threats.

But this system is built on a cycle of activation followed by recovery. When stress is sustained (weeks of deadline pressure, an extended crisis, months of overload) the recovery phase never arrives. The immune system shifts in a different direction entirely: suppressed cellular immunity, reduced antibody responses, and an impaired ability to regulate inflammation. The system doesn’t stay switched on. It becomes dysregulated.

This is why illness often arrives right as the stressor lifts. During the high-stress period, the body is running on a kind of borrowed immune readiness, adrenaline and cortisol keeping things functioning under pressure. The moment that pressure releases, the body’s resources reallocate, the masking effect of acute stress hormones fades, and the immune suppression that’s been building underneath becomes apparent. The illness wasn’t caused by the stress ending, it was caused by the stress itself, and the ending is just when your body finally has room to register it.

The practical implication isn’t to avoid stressful periods as most aren’t avoidable. It’s to actively support recovery once the acute period ends, rather than immediately filling the newly available time and energy with something else. Sleep, hydration, and nutrient-dense food in the days immediately following a high-stress period aren’t indulgent. They’re giving the immune system the recovery window it’s been waiting for.

A Massive Genetics Study Just Reshaped How We Understand Why Mental Health Conditions Overlap

This finding is more foundational than most of what I cover, but it has direct relevance for anyone who’s noticed that anxiety, depression, ADHD, and other conditions seem to travel together more often than chance would suggest.

A massive global genetics study analysing data from more than six million people found deep genetic connections across 14 psychiatric conditions, reshaping the understanding of why mental health diagnoses so often co-occur in the same person. Rather than 14 separate, unrelated conditions that happen to sometimes appear together, the genetic architecture suggests significant shared biological underpinnings across conditions that have historically been classified and treated as entirely distinct.

This matters practically for a few reasons. First, it helps explain something many people experience and don’t have language for: having both anxiety and ADHD, or depression alongside an eating disorder, isn’t a sign of being “more broken,” it reflects overlapping genetic and biological vulnerability that researchers are only now mapping properly. Second, it suggests that effective treatments for one condition in this overlapping cluster may have more crossover benefit for related conditions than previously assumed, which is consistent with what we’ve covered before regarding exercise’s broad effect across both depression and anxiety, and gut microbiome interventions showing benefit across multiple mood-related conditions.

This is genetics research, not a treatment finding, it doesn’t change what to do today. But it’s worth knowing because it reframes a common experience: if you’ve ever felt like your mental health doesn’t fit neatly into one diagnostic box, the underlying biology may genuinely not separate as cleanly as the diagnostic categories suggest it should.

Anxiety and Insomnia Are Linked to a Measurable Drop in a Specific Immune Cell. In Young Women Specifically

This finding connects directly to the immune-stress research above, but with more specificity, and it’s worth knowing on its own.

A study of young women in Saudi Arabia found that both anxiety and insomnia were linked to significantly fewer natural killer cells, a type of immune cell that acts as the body’s rapid-response team, providing frontline defence against infected and abnormal cells.

Natural killer cells are part of the innate immune system meaning they don’t need to “learn” a threat first; they respond immediately. A measurable reduction in their numbers represents a real decrease in the body’s immediate defensive capacity, not a subtle or theoretical effect.

This adds a concrete mechanism to something many women already sense intuitively: that periods of high anxiety and poor sleep coincide with getting sick more easily, healing more slowly, and generally feeling more physically vulnerable and not just more tired. The natural killer cell finding gives that intuition a measurable biological basis rather than leaving it as a vague feeling.

This is also a two-way relationship worth being aware of, similar to the stress-skin loop covered in a previous edition: poor sleep and anxiety reduce immune defence, and a weakened immune state can itself contribute to the kind of low-grade inflammation that worsens anxiety and disrupts sleep further. Breaking into this loop at any point, improving sleep specifically, even before anxiety itself feels manageable has a documented basis for supporting immune recovery, not just feeling more rested.

A Popular Supplement May Increase Birth Defect Risk. Worth Knowing Even If Pregnancy Isn’t on Your Mind Right Now

This finding is specific and worth flagging clearly, because the supplement involved is widely used and widely perceived as completely harmless.

A new study found that high doses of certain antioxidant supplements including NAC (N-acetylcysteine), commonly used for liver support, respiratory health, and as a general antioxidant, may carry risks for future offspring that weren’t previously well understood. In the study, male mice given common antioxidant supplements at high doses produced offspring with subtle but significant facial and skull structural changes — an effect that researchers hadn’t anticipated given antioxidants’ generally benign reputation.

This is animal research, and the dose levels used were higher than typical human supplemental use, both important caveats. But the finding matters because it challenges a common and largely unexamined assumption: that antioxidant supplements are essentially risk-free because they’re “natural” or because their general mechanism (reducing oxidative stress) sounds protective rather than harmful.

The practical relevance, even outside of active pregnancy planning: supplement safety research specific to reproductive outcomes is still emerging, and high-dose supplementation of anything, even substances generally considered safe deserves more scrutiny than it typically receives, particularly for anyone who is, might become, or is trying to become pregnant, or whose partner is in that category. “More is better” doesn’t reliably apply to antioxidants any more than it applies to vitamins generally, and this is a useful, concrete example of why.

The information in this post is for educational and informational purposes only. None of the above constitutes medical advice. Always consult a qualified healthcare professional for personal health concerns.

Between Saturdays is a weekly research roundup from Simply Salvia. Four things from science and wellness worth knowing about. If someone sent this to you, you can subscribe here.

Detailed Readings

Psychological Stress and the Human Immune System: A Meta-Analytic Study of 30 Years of Inquiry

Scientists discover why mental disorders so often overlap

Anxiety and insomnia linked to sharp drops in key immune cells

This popular supplement may increase risk of birth defects, study finds

Part 1 ended at the evidence hierarchy, which told you that most of what’s being sold is not at the top of it, and what actually is.

Part 2 is the practical half. The specific blood tests to ask for and the numbers that actually matter for hair health. The treatment guide, including everything you need to know about minoxidil. What the supplements actually do in which situations. And the complete month-by-month guide to a recovery that has a realistic timeline attached to it.

4. The Blood Tests to Request. And What the Numbers Actually Mean

5. The Full Treatment Guide. What the Research Supports and How to Use It

6. What the Supplements Actually Do, By Situation

7. The Cycle-Aware Approach. The Weeks Where Shedding Is Reliably Worse

8. The Complete Practical Guide

9. Conclusion: The Guide Your GP Probably Didn’t Have Time to Give You

   This Substack is reader-supported. To receive new posts and support my work, consider becoming a free or paid subscriber.

Read more

Caught My Eye…

Endometriosis Isn’t a Reproductive Disease. It’s a Whole-Body Inflammatory Disease. And That Reframe Changes Everything.

For decades, endometriosis has been treated as a gynaecological condition - tissue similar to the uterine lining growing where it shouldn’t, causing pain, mainly during periods. A research finding from March 2026 is pushing the field toward a fundamentally different understanding, and the implications are significant.

A study found that people with endometriosis were about twice as likely to be diagnosed with an autoimmune disease, such as lupus or multiple sclerosis, within two years of their endometriosis diagnosis. This doesn’t mean endometriosis is itself an autoimmune disease but it suggests the two share underlying problems, including ongoing inflammation and changes in immune system function.

A growing body of research now shows that endometriosis is not solely a reproductive condition or a “bad period.” It’s a multi-system, inflammatory disorder with effects throughout the body. The overlapping features; chronic inflammation, dysregulated immune cell activity, and problems with the immune system recognising the body’s own tissue correctly, strengthen the case for understanding it as a systemic immune disorder.

This matters beyond academic classification. Many of the genes involved in endometriosis are also linked to other pain and inflammatory conditions; migraines, chronic back pain, asthma, and osteoarthritis. This raises the possibility that existing treatments for those conditions, already tested and understood, could be repurposed for endometriosis, a much faster path to new treatment options than starting from scratch.

The diagnostic delay remains one of the most troubling aspects of this condition. Endometriosis affects more than 170 million women worldwide, with up to 1 in 10 women of reproductive age believed to have the condition and yet an estimated 60% of cases remain undiagnosed. Diagnostic delay averages 7 to 9 years after first symptoms, and there are currently no reliable biomarkers meaning diagnosis still typically requires invasive laparoscopic surgery.

There’s real movement on this front too. Researchers are developing a non-invasive scan to diagnose endometriosis, with the potential to significantly reduce diagnostic delays and remove the need for invasive procedures. Globally, research is also exploring diagnostic approaches using menstrual blood, saliva, and other emerging technologies.

What this means if period pain has ever been dismissed as normal: pain severe enough to affect daily function, school, or work is not something you should have to simply endure. The “it’s just a bad period” framing has likely contributed to the diagnostic delay this condition is now infamous for. If your periods involve pain that paracetamol and a hot water bottle don’t touch, pain that radiates beyond the pelvis, or symptoms that don’t track neatly with bleeding alone, this is worth raising directly and specifically with a doctor — not as something to push through.

ADHD Symptoms in Women Change Across the Menstrual Cycle. Almost Nobody Diagnosing ADHD Is Asking About This.

This is one of the more striking research findings to come out this year, and it has real implications for how ADHD is assessed in women.

A world-first study examining ADHD in women across their lifespan found there may be systemic misdiagnosis and underdiagnosis of women rather than ADHD genuinely being more common in men. The standout finding: 88% of women surveyed reported changes in their ADHD symptoms during their menstrual cycle, particularly in the latter two weeks of the cycle aka the luteal phase.

The hormonal mechanism is becoming clearer. Dopamine (one of the neurotransmitters most directly implicated in ADHD) interacts with both estrogen and progesterone. As estrogen rises in the follicular phase, dopamine signalling tends to be more efficient so symptoms often feel more manageable. As estrogen falls in the late luteal phase, that support diminishes, and ADHD symptoms like difficulty concentrating, impulsivity, emotional dysregulation, frequently intensify. This is a distinct and separate phenomenon from generic premenstrual mood changes; it’s a hormonally-mediated fluctuation in symptom severity for a condition that’s already present year-round.

The transitions matter just as much as the monthly cycle. More than 70% of women surveyed said their ADHD symptoms worsened after having a baby, and almost all women (97%) said their symptoms were exacerbated during menopause. ADHD symptoms can worsen during the postpartum period and through perimenopause, accompanied by increased mood and sleep disturbances and these patterns have historically been overlooked, contributing to underdiagnosis and misdiagnosis.

This has a particularly important implication for women diagnosed with ADHD later in life, often in their 30s, 40s, or during perimenopause. Perimenopause can unmask ADHD traits that were previously kept in check by structure, support, or sheer effort. For many women, hormonal change is the first time the strategies that worked for years stop being enough. This isn’t menopause causing ADHD, it’s the hormonal shift removing the compensatory scaffolding that was masking a lifelong pattern.

The practical implication: if ADHD assessment or medication review doesn’t take menstrual cycle phase into account, it may be missing a significant part of the picture. Researchers are now recommending cycle tracking alongside validated symptom questionnaires as part of a more accurate assessment protocol for women. If you’re already diagnosed and notice your symptoms are markedly worse in the two weeks before your period, this isn’t inconsistency in your condition, it’s a documented hormonal pattern worth discussing with whoever manages your treatment.

Heart Disease Risk in Type 2 Diabetes Looks Completely Different in Women Than in Men

This finding deserves more attention than it’s getting. Type 2 diabetes substantially raises cardiovascular risk in everyone but the way that risk plays out, and the symptoms that signal it, differ meaningfully by sex.

A major study covered by ScienceDaily in early 2026 examined how cardiovascular risk in type 2 diabetes diverges between men and women and the differences are significant enough to affect how risk should be screened for and discussed with women specifically. Women with type 2 diabetes have historically been found to lose more of the natural cardiovascular protection that estrogen provides pre-menopause compared to men’s baseline risk trajectory, meaning a diabetes diagnosis can represent a proportionally larger jump in cardiovascular risk for women than the same diagnosis represents for men.

This connects to a pattern that’s been documented across cardiovascular research generally: women’s heart attack symptoms are less likely to be the “crushing chest pain” most people associate with cardiac events, and more likely to present as fatigue, nausea, jaw pain, or breathlessness, symptoms that get attributed to anxiety or stress far more often in women than in men, as covered in an earlier Between Saturdays.

For women with type 2 diabetes, PCOS, or a family history of early cardiovascular disease, this combination, atypical symptom presentation plus a disproportionate cardiovascular risk increase from diabetes is a real gap in standard care. The practical takeaway: a cardiovascular risk conversation with a GP shouldn’t wait for traditional risk factors alone (high cholesterol, smoking, obvious chest symptoms). Family history, PCOS, gestational diabetes history, and blood sugar patterns are all relevant data points worth bringing into that conversation explicitly, particularly for women under 50 who don’t fit the traditional cardiac risk profile.

Menopause and Brain Structure: The Follow-Up Research Is Getting More Specific

I covered the initial February 2026 finding on menopause and grey matter loss in an earlier edition. The research has continued to develop since, and it’s worth a fuller look now that more data exists.

The original study found that menopause is linked to measurable changes in brain structure, with grey matter loss in regions tied to memory and emotional regulation alongside changes in mental health and sleep. Subsequent research from Cambridge has continued to build out this picture, linking the menopausal transition specifically to changes in brain structure, sleep disruption, anxiety, and cognitive symptoms as an interconnected cluster rather than separate, unrelated complaints.

This reframing matters for a specific reason: brain fog, memory lapses, and mood changes during perimenopause have historically been treated as vague, subjective complaints and sometimes dismissed entirely, sometimes attributed to stress or ageing generically. The structural brain imaging data suggests these experiences may reflect real, measurable physiological changes happening during the hormonal transition, not just a subjective shift in how women are coping with midlife generally.

The “timing hypothesis” continues to be the most actionable finding from this research line: the neuroprotective effects of oestrogen and by extension, the protective effects of hormone therapy when started early in the menopausal transition, appear to be greatest when intervention happens before significant structural changes have accumulated, rather than waiting until much later in life. This adds further weight to a conversation we’ve covered before: HRT decisions framed only as a late-life option may be missing a window where the neurological benefits are most significant.

For women in perimenopause experiencing what feels like a real cognitive shift and not “I’m just getting older” but a genuine change in mental clarity, word-finding, or memory this research is validating that the experience may be measurable and real, and is worth raising directly rather than minimising.

The information in this post is for educational and informational purposes only. None of the above constitutes medical advice. Always consult a qualified healthcare professional for personal health concerns.

Between Saturdays is a weekly research roundup from Simply Salvia. Four things from science and wellness worth knowing about. If someone sent this to you, you can subscribe here.

Detailed Readings

Endometriosis: new insights and opportunities for relief of symptoms

ADHD and Sex Hormones in Females: A Systematic Review

Why heart disease risk in type 2 diabetes looks different for men and women

Menopause linked to grey matter loss in key brain regions

Then it was the shower drain. Then the pillow. Then the ponytail that felt noticeably thinner in my hand than it used to. By the time it was obvious enough to worry about, it had been happening for months.

This is how hair loss usually goes for women. Quietly at first, then all at once. And the information available when you finally start looking? Either terrifying, or trying to sell you something.

This short dive is the guide I wanted then. What’s actually happening. Why it happens to women specifically. What the research says works and what it says about the expensive supplements and serums that dominate this space. And, the practical framework: the blood tests to ask for, the treatments with real evidence, and the honest timeline.

Let’s start with the biology.

1. How Hair Actually Grows And Why That Determines Everything

2. The Most Common Causes in Women Under 35

3. The Evidence Hierarchy. What the Research Says Actually Works

Chapter 1: How Hair Actually Grows And Why That Determines Everything

The Hair Cycle

Every single hair on your head is going through its own independent cycle -completely separate from the hairs around it. And understanding this cycle is the key to understanding why hair loss happens the way it does: why it’s delayed, why it’s diffuse, and why recovery takes so much longer than you’d expect.

The cycle has three phases:

Anagen: the growth phase

This is when the hair is actively growing. Each strand spends between two and seven years in anagen, growing approximately 1cm per month. The length your hair can reach is largely determined by how long your follicles stay in anagen, which is partly genetic.

Catagen: the transition phase

A brief two-week window where the hair stops growing and the follicle starts to shrink and detach from its blood supply. Only about 1% of hairs are in this phase at any given time.

Telogen: the resting phase

The hair is no longer growing but is still attached to the follicle. It stays here for approximately three to four months before being shed and replaced by a new anagen hair growing underneath. About 10–15% of your hairs are in telogen at any one time.

Normally losing between 50 and 100 hairs per day is considered completely normal. These are the telogen hairs that have completed their cycle. The reason you don’t go bald is that only a small percentage of follicles are in this phase at any time, and the majority are actively growing.

Why Hair Loss Is Always Delayed

Here’s the thing that catches almost everyone off guard: whatever caused your hair loss happened two to three months before you noticed it.

When something goes wrong whether it’s a physical stressor, a hormonal shift, an illness, a period of severe restriction, a crash diet. The body’s response is to push a large number of hair follicles out of anagen and into telogen simultaneously. But those hairs don’t fall out immediately. They sit in the telogen resting phase for two to three months before they’re shed.

This means that by the time the hair is coming out in handfuls in the shower, the trigger already happened months ago. Which is why people so often struggle to identify what caused it. The event felt unrelated because it happened before the shedding started.

A 2025 review of 2,851 female telogen effluvium patients confirmed this two-to-three month delay as the consistent pattern across thousands of cases. The trigger and the shedding are temporally disconnected in a way that makes the cause genuinely difficult to identify without understanding the biology.

Normal Shedding vs. Actual Hair Loss - The Difference

The distinction matters because panic about normal shedding is common and it’s useful to know what you’re actually dealing with.

Normal shedding: Diffuse, even hair loss across the whole scalp. 50–100 hairs per day. The hair that comes out has a white bulb at the root (a telogen hair, it completed its cycle). No change in the density of your part or hairline. No patches.

Telogen effluvium (shedding disorder): More than 100–150 hairs per day, usually after a trigger. Often visible at the part line (which appears wider) or in the ponytail (which appears thinner). The hairs lost have white bulbs, they’re telogen hairs that were pushed out of their cycle early. Temporarily elevated, usually reversible.

Female pattern hair loss (androgenetic alopecia): Gradual thinning over months or years, primarily at the crown and widening of the part. The hairs lost are progressively finer and shorter, miniaturised by androgen activity at the follicle. Less diffuse than TE, more patterned. Responds to different treatments.

Alopecia areata: Patchy, often sudden hair loss in distinct circular areas. Autoimmune in origin, the immune system attacks hair follicles. Requires medical assessment.

Most young women experiencing sudden, diffuse hair shedding have telogen effluvium, which is reversible once the trigger is identified and addressed. The first job is identifying what caused it.

Chapter 2: The Most Common Causes in Women Under 35

Iron Deficiency - The Most Common and Most Missed

This is the one I most want you to know about because it’s the most common nutritional cause of hair loss in young women, the most consistently documented in research, and the most routinely missed by standard blood tests.

Iron plays a critical role inside the hair follicle. It’s required for DNA synthesis - the process that lets follicle cells divide and produce new hair. When iron stores are low, the follicle prioritises essential functions and hair production gets deprioritised. Follicles shift into telogen early, shedding increases, and new hair grows in finer and more slowly.

The important distinction: the blood test that GPs most commonly run is haemoglobin, which tests for anaemia. But you can be iron-deficient without being anaemic. Your haemoglobin can be completely normal while your iron stores are nearly empty. Only 32% of women with chronic telogen effluvium in one study were anaemic but 86% had low ferritin. Ferritin is the protein that stores iron, and it depletes long before haemoglobin falls.

A meta-analysis of 36 studies involving over 10,000 women found that those with hair loss had significantly lower ferritin levels than those without, on average 18 ng/mL lower. The critical threshold most dermatologists now use for hair loss specifically is ferritin below 40 µg/L but the standard lab reference range for “normal” ferritin often starts at 12 or 15 µg/L. This means you can receive a “normal” result while sitting at a level that’s driving hair loss.

Women aged 15–35 are disproportionately affected because of menstrual blood loss. Menstruation depletes iron monthly, and if dietary intake isn’t replacing what’s lost, which is genuinely difficult without red meat on a typical Western diet, ferritin gradually depletes over months or years. Iron deficiency affects approximately 72% of women experiencing hair loss, making it the single most common underlying factor.

What to do: Ask for ferritin specifically and not just a full blood count or haemoglobin. Ask what your result is rather than just whether it’s “normal.” If it’s below 40 µg/L, discuss iron supplementation with your GP.

Dietary iron: red meat is the most bioavailable source; lentils, chickpeas, spinach, pumpkin seeds, and sardines for plant-based sources. Always pair plant-based iron with vitamin C. Avoid tea and coffee within an hour of iron-rich meals.

Stress - The Mechanism Is More Specific Than You’ve Been Told

Stress-related hair loss is real, documented, and follows a predictable biological pattern. But “stress causes hair loss” is too vague to be useful. Here’s the specific mechanism.

Cortisol (the main stress hormone) affects hair follicles directly. A 2025 paper in JAAD Reviews detailed how cortisol, the HPA axis, inflammatory cytokines, and neuropeptides mediate telogen effluvium and found a particularly cruel feedback loop: stress triggers TE, but the psychological distress of watching your hair fall out maintains and amplifies the stress response that caused the shedding. The hair loss and the stress feed each other.

When the body is under significant stress, approximately 70% of anagen hairs can be pushed into telogen simultaneously far more than the usual 10–15%. This produces the alarming shower-drain level of shedding that most people don’t connect to the period of burnout or acute stress that happened two months earlier.

Both acute stress (a major life event, illness, surgery) and chronic stress (sustained work overload, long-term sleep disruption, ongoing emotional strain) can trigger TE but they do so through overlapping mechanisms. A 2025 Cureus review identified a newly understood pathway: chronic psychological stress impairs mitochondrial function in follicular cells, accelerating the shift out of the growth phase through oxidative stress. This is a structural cellular effect, not just a “stress response.”

The good news: Stress-triggered TE is almost always reversible. Once the trigger is removed and the body recovers, follicles return to anagen. Shedding typically slows within three to six months after the stressor resolves, and regrowth begins. Full cosmetic recovery takes 12 to 18 months, because hair grows slowly regardless of how well the follicles are functioning. The timeline is longer than most people expect, which creates the impression that recovery isn’t happening when it actually is.

Hormonal Shifts; Postpartum, Post-Pill, and the Cycle

Postpartum hair loss is the textbook example of hormonally triggered TE. During pregnancy, estrogen rises significantly and keeps a much higher percentage of hairs in the anagen (growth) phase, which is why many women’s hair is thicker and more lustrous when pregnant. After birth, estrogen drops sharply. The hairs that were held in anagen by elevated estrogen all transition to telogen simultaneously. Two to four months later, the shedding arrives and for new mothers in an already exhausted, depleted state, it can be severe.

Postpartum TE is almost universally self-resolving. The follicles are healthy. The trigger; the hormonal shift was a one-time event. Given adequate nutrition (particularly iron and protein, which are often depleted in the postpartum period), recovery is the expected outcome.

Post-pill shedding follows the same mechanism. The combined oral contraceptive pill maintains artificially elevated synthetic hormones. When it’s stopped, those hormones drop and the hair that was held in anagen by the pill’s hormonal environment transitions to telogen. The shedding typically begins six to twelve weeks after stopping the pill and can last three to six months. Again, self-resolving once the body establishes its natural hormonal rhythm.

The menstrual cycle and hair shedding is a less discussed but real phenomenon. Research published in the British Journal of Dermatology examining 17,009 women found significant skin and hair condition changes associated with menstrual cycle irregularity. The luteal phase (the two weeks before the period) is when estrogen is falling and progesterone is dominant. Some women notice increased shedding in this window. This is hormonal fluctuation affecting the follicle environment at a cycle level rather than a structural hair loss condition. Notably worse in the context of iron deficiency, which amplifies the follicular sensitivity.

PCOS creates chronic androgen excess (elevated testosterone and DHT) which miniaturises hair follicles on the scalp (androgenetic alopecia pattern) while simultaneously causing excess hair growth elsewhere. If hair loss follows a pattern of central and crown thinning with widening of the part, and you have other PCOS symptoms (irregular cycles, acne, excess body hair), this is the conversation to have with a GP.

Other Causes Worth Knowing

Thyroid dysfunction: Both hypothyroidism (underactive) and hyperthyroidism (overactive) are associated with diffuse hair loss. The thyroid regulates cellular metabolism, including the metabolic activity of hair follicles. Thyroid issues are more common in women than men and are frequently underdiagnosed. An October 2025 study of 100 women with hair loss found significantly different thyroid hormone profiles in the hair loss group compared to controls. TSH (thyroid-stimulating hormone) is the standard test; ask for this alongside ferritin if diffuse hair loss has no obvious trigger.

Rapid weight loss or severe calorie restriction: The body deprioritises hair production under significant energy deficit. This is one of the mechanisms behind TE in eating disorders and crash dieting. The follicles are not damaged, they’ve simply been put into conservation mode. Recovery requires restoring adequate nutrition and calorie intake.

Vitamin D deficiency: Increasingly documented as a contributing factor. Vitamin D receptors are present in hair follicles, and deficiency is associated with accelerated follicle miniaturisation and slower regrowth. Worth including in any hair loss blood panel.

Protein deficiency: Hair is made almost entirely of keratin - a protein. Inadequate dietary protein provides insufficient building material for hair production, particularly relevant for women on very low-calorie or low-protein diets.

Chapter 3: The Evidence Hierarchy. What the Research Says Actually Works

This chapter is the one that differs most from what’s being sold to you.

The hair loss supplement and serum industry is enormous. Biotin gummies, collagen powders, “hair growth vitamins,” scalp serums with seventeen ingredients. The marketing is compelling and the evidence behind most of it is thin. Here’s what the research actually ranks.

What Has Strong Evidence

Minoxidil: the strongest evidence for hair growth in women

Minoxidil was originally developed as a blood pressure medication. One of its side effects was hair growth and that side effect became the treatment. It works by prolonging the anagen phase of the hair cycle and increasing blood flow to follicles, giving them a better nutrient supply.

5% topical minoxidil is FDA-approved for female hair loss. A 2025 meta-analysis of randomised clinical trials found that oral minoxidil at low doses (0.25–2.5mg daily for women) produced comparable or superior hair regrowth to topical minoxidil, with good tolerability at low doses. A JAMA Dermatology consensus statement in January 2025 from an international panel established best practice guidelines for low-dose oral minoxidil, signalling its acceptance as a mainstream treatment rather than a fringe one.

The honest caveats: minoxidil works while you use it. If you stop, hair that was maintained by it will shed again within a few months. It requires commitment to ongoing use. It also takes three to six months to show meaningful results - shorter than the recovery timeline from TE, but still requiring patience. And low-dose oral minoxidil requires a GP prescription and cardiac screening for anyone with a relevant medical history.

Addressing the underlying cause first. If hair loss is driven by iron deficiency, no topical treatment will fully compensate. Restoring ferritin is the primary intervention and once levels are adequate, the follicles resume normal function. Same logic applies to thyroid dysfunction, severe dietary restriction, and hormonal disorders. The treatment must match the cause.

What Has Reasonable Evidence

Iron supplementation (when deficient)

Not as a supplement for everyone (iron toxicity is a real risk) but for women with confirmed low ferritin, supplementation is well-evidenced for supporting hair regrowth. The form matters: ferrous fumarate or ferrous sulfate are well-absorbed; ferrous gluconate is gentler on the stomach if the others cause GI issues. Taken with vitamin C, away from tea and coffee.

Zinc

Hair loss patients consistently show lower zinc levels than controls. The October 2025 study of 100 women with hair loss found significantly lower zinc in the hair loss group. Zinc plays a role in follicle cell division and the hair growth cycle. However, excessive zinc supplementation suppresses copper absorption and can cause its own problems, supplementation should be guided by blood levels rather than taken speculatively.

Vitamin D

As above - worth testing, worth supplementing if deficient. 1,000–2,000 IU daily is well-evidenced as safe for most adults at low to moderate deficiency.

What the Research Doesn’t Strongly Support

Biotin

The biotin-hair growth connection is one of the most heavily marketed claims in the supplement industry.

The evidence: biotin deficiency (genuinely rare) is associated with hair loss, and correcting it helps. But supplementing biotin above adequate levels in people who are not deficient has no demonstrated effect on hair growth or retention. Most people consuming a typical diet are not biotin-deficient. Biotin supplements are being purchased on the basis of a mechanism (deficiency = hair loss) that doesn’t apply to the people buying them. They also interfere with thyroid and cardiac blood tests.

Collagen supplements for hair growth

Collagen provides amino acids that are building blocks for hair keratin. The indirect logic makes sense. The clinical evidence for oral collagen supplementation specifically producing measurable hair growth is thin. There are better and cheaper ways to get protein.

Most proprietary “hair growth vitamin” blends

Usually contain biotin (not evidenced for non-deficient individuals), some B vitamins (useful only if deficient), and various botanicals (saw palmetto, DHT-blocking herbs) at doses too low to produce the effects claimed. Save the money for ferritin testing or an actual treatment.

Scalp serums with “growth-stimulating” ingredients (rosemary oil, caffeine serums, peptides)

Some preliminary evidence exists for rosemary oil, one small study found it comparable to 2% minoxidil at 6 months. It’s not evidence of strong efficacy; it’s evidence that it might do something. Caffeine applied to the scalp has some in-vitro evidence for blocking DHT at the follicle. None of this is at the level of minoxidil evidence. These can be incorporated into a routine, but they are not treatments.

Part 1 ends here. Part 2 is the practical half: the blood tests to request, the full treatment guide, the supplement breakdown, how to build a recovery routine, and the cycle-aware approach for the weeks when shedding is reliably worse.

Now you understand what’s actually happening. The hair cycle and why loss is always delayed. The causes most common in women under 35; iron deficiency (the one most GPs miss), stress (with a more specific mechanism than you’ve been told), hormonal shifts, and thyroid. And the evidence hierarchy for treatment, which looks very different from what the supplement industry presents.

Part 2 takes all of this and makes it actionable.

Chapter 4 is the blood test guide. Exactly what to ask for, what the numbers mean, and what the targets are for hair health specifically versus the standard “normal” ranges.

Chapter 5 is the full treatment guide. Minoxidil in detail (topical versus oral, what to expect, the timeline), what the hormonal treatments do, and the honest assessment of every other intervention in the space.

Chapter 6 is the supplement chapter. What the evidence actually says about biotin, collagen, zinc, iron, vitamin D, and the “hair growth blends,” with the specific scenarios where each one makes sense and the ones where you’re wasting money.

Chapter 7 is the cycle-aware approach. How to support your follicles in the weeks where shedding is hormonally worse, what dietary and lifestyle interventions the research backs for the luteal phase specifically.

Chapter 8 is the complete practical guide: the daily routine for hair health, what to do in months one through twelve, and when to stop trying to manage this yourself and see a dermatologist or trichologist instead.

Subscribe to read Part 2 →

Sources & Further Reading

Karakoyun et al. Retrospective Review of 2851 Female Patients With Telogen Effluvium — Journal of Cosmetic Dermatology, February 2025

Sunil & Zacharia. Clinical profile of female patients with chronic telogen effluvium and its association with serum ferritin level — Asian Journal of Medical Sciences, December 2024

Iron deficiency and nonscarring alopecia in women — meta-analysis, Skin Appendage Disorders, 2022 (36 studies, 10,000+ women)

Mdanat et al. Quantitative analysis of circulating biomarkers in females with hair loss — Nutrients, October 2025

Hughes, Syed & Saleh. Telogen Effluvium — StatPearls, NIH, 2024 update

Shapiro Medical. Hair loss from stress and telogen effluvium — mechanism review, 2025–2026 research

Sobral et al. Efficacy and safety of oral vs topical minoxidil — meta-analysis of RCTs, International Journal of Dermatology, 2025

Akiska et al. Low-dose oral minoxidil initiation consensus statement — JAMA Dermatology, January 2025

Olsen et al. Summation and recommendations for topical and oral minoxidil — JAAD, August 2025

Löffler et al. Omega-3 fatty acid deficit in acne patients — PMC, 2024

Lau et al. Physiological differences in sebum composition in menstruating women — Journal of Dermatology, August 2025

Caught My Eye…

Body Temperature Is Your Most Underrated Sleep Tool

Sleep researchers talk about body temperature far less than they talk about screens, supplements, and sleep schedules. They should probably swap those priorities.

Your core body temperature needs to drop by approximately 1–1.5°C from its daily peak to initiate and maintain deep, slow-wave sleep. This isn’t a small adjustment, it’s a significant physiological shift that the body actively manages through a process called distal vasodilation: blood is sent to the hands and feet, where heat can radiate away from the body, cooling the core. This is why warm hands and feet are associated with faster sleep onset. The heat is redistributing from the centre outward.

Several things interfere with this process in ways that most sleep content doesn’t address:

A warm bedroom. The optimal sleeping temperature for deep sleep is approximately 18–19°C (65–67°F) for most people. Research from the Sleep Foundation and multiple sleep labs found that room temperatures above 24°C significantly increase waking during the night and reduce slow-wave sleep time. Sleeping hot is one of the most common and least discussed causes of fragmented sleep.

The luteal phase of the menstrual cycle. As covered in the sleep deep dive: progesterone raises resting body temperature by 0.3–0.7°C in the two weeks before a period. When the baseline is already elevated, the body has less temperature range to drop through on the way to deep sleep. This is the primary mechanism behind the sleep fragmentation that most women notice in the premenstrual window.

Alcohol. Alcohol initially causes peripheral vasodilation, it feels relaxing because it redistributes heat but as it metabolises, it disrupts the temperature regulation required for sustained deep sleep and produces arousal in the second half of the night.

A warm bath or shower 60–90 minutes before bed works paradoxically: it heats the skin surface, accelerating peripheral vasodilation, which speeds up the cooling of the core. The bath doesn’t make sleep better because it relaxes you. It makes sleep better because it accelerates the physiological temperature drop that deep sleep requires.

Practical for right now: make your bedroom colder than you think you need to. Research suggests most people sleep at temperatures 3–5°C higher than is optimal. The discomfort of a cool room lasts about two minutes before you’re under a duvet and the sleep is measurably better.

The Stress-Skin Connection Is a Loop, Not a Line

Most content on stress and skin treats it as a one-way relationship: stress raises cortisol, cortisol disrupts your skin. That’s true, but it’s only half the picture. The full picture is a feedback loop and understanding the loop changes what you do about it.

Chronic stress raises cortisol. Cortisol degrades collagen, increases sebum production, disrupts the skin barrier, and suppresses the overnight repair processes that depend on deep sleep and growth hormone. This produces reactive, acne-prone, dull, or inflamed skin.

Here’s the other half: skin conditions themselves activate the stress response. Dermatology research has consistently found that inflammatory skin conditions like acne, eczema, rosacea, psoriasis, elevate psychological stress, which in turn elevates cortisol, which worsens the skin condition, which elevates stress further. The loop feeds itself from both directions.

This explains why people with stress-driven skin conditions often find that topical treatments produce improvement but not resolution. The topical intervention is addressing the skin end of the loop without addressing the nervous system end. The cortisol that’s driving the barrier disruption, the sebum overproduction, or the inflammatory flare is being re-generated continuously by the stress loop that the product can’t reach.

Research from 2025 examining psychodermatology interventions found that cognitive behavioural therapy and mindfulness-based stress reduction produced measurable improvements in inflammatory skin conditions, independent of any topical treatment. The mechanism is direct: reducing HPA axis activation reduces the cortisol signal to the skin. Less cortisol means less sebum production, less barrier disruption, better overnight repair, less inflammation.

The most powerful single intervention for this specific pattern is sleep. A single night of sleep deprivation measurably elevates cortisol and inflammatory markers. Chronic poor sleep maintains the cortisol elevation that keeps the skin loop running. No topical product can compensate for what consistently disrupted sleep is doing to the hormonal environment the skin has to function within.

This is the real sequence:

The entry point to this loop, for most people, is sleep. Not a new serum.

The Exercise Snack Research Is Genuinely Interesting

“Exercise snacking,” short bouts of physical activity (typically 2–10 minutes) spread across the day rather than consolidated into one workout, has accumulated a surprisingly strong evidence base over the past two years, and it matters specifically for people who struggle to maintain longer exercise sessions.

A 2025 systematic review found that exercise snacks specifically short bouts of vigorous stair climbing, brisk walking, or bodyweight exercises performed 2–3 times per day produced measurable improvements in cardiovascular fitness (VO2max), blood sugar regulation, and insulin sensitivity comparable to longer, continuous moderate exercise. The key finding: accumulated short bouts appear to produce similar or equivalent metabolic benefits to a single longer session of equivalent total duration.

For women specifically, there’s an additional angle: the blood sugar spike that follows meals can be meaningfully reduced by a 2–5 minute walk within 30 minutes of eating. Research published in Sports Medicine found that post-meal walking (even very short duration) significantly blunted post-meal glucose responses compared to sitting. The mechanism: muscle contraction uses glucose directly from the bloodstream as fuel, reducing the amount of work insulin has to do.

This matters practically because the meal-to-meal blood sugar swings that drive cravings, energy crashes, and the luteal phase blood sugar instability I’ve covered repeatedly in Simply Salvia are most effectively managed at the point of the meal and not through general lifestyle changes that work on a longer timescale.

The honest caveat: exercise snacking is not a replacement for progressive resistance training for body composition, bone density, and long-term metabolic health. The evidence supports it as an effective strategy for people with limited time or access, or as an addition to a broader movement practice and not as a complete substitute. Walking after meals and taking the stairs consistently are genuinely useful habits with evidence behind them. They are not a replacement for 2–3 weekly resistance sessions.

The Inflammation Biomarker Most Young Women Have Never Heard Of

CRP (C-reactive protein) is a blood marker of systemic inflammation. It’s produced by the liver in response to inflammatory signals from anywhere in the body; infection, injury, autoimmune activity, or chronic low-grade inflammation from lifestyle factors. It’s included in standard blood panels in some countries and omitted in others, and most women in their 20s and 30s have never had it discussed with them.

Here’s why it matters:

Low-grade chronic inflammation, reflected in mildly elevated CRP is one of the most consistent underlying mechanisms in the conditions that most affect young women:

• Depression and anxiety (elevated inflammatory cytokines are found in a significant subset of both),

• Acne and inflammatory skin conditions,

• Menstrual irregularity and painful periods (prostaglandin-driven pain is an inflammatory process), and

• Insulin resistance and metabolic dysfunction.

A 2025 analysis found that CRP levels in young adults are rising, driven by increasing rates of ultra-processed food consumption, sleep disruption, sedentary behaviour, and chronic psychological stress. This isn’t a condition with obvious symptoms. It’s a background state of heightened immune activation that quietly makes all of the above conditions harder to manage and more severe.

The factors with the strongest evidence for reducing CRP in healthy young women:

These are the same interventions that show up across every category of women’s health research, not because wellness content keeps repeating the same things, but because chronic systemic inflammation is genuinely at the root of a wide range of conditions and these interventions address it at the source.

The things with the strongest evidence for raising CRP:

• Ultra-processed food,

• Sleep deprivation,

• Physical inactivity,

• Abdominal obesity, and

• Smoking.

These, too, are the same factors that show up repeatedly in the risk literature across multiple conditions. The biological mechanism connecting them all is inflammation.

If your GP runs a full metabolic panel and CRP isn’t included: ask for it specifically. A high-sensitivity CRP (hs-CRP) below 1 mg/L is low risk. 1–3 mg/L is moderate. Above 3 mg/L is elevated and worth investigating. It won’t be discussed unless you ask, but it tells you more about your background inflammatory state than most of the other markers routinely measured.

The information in this post is for educational and informational purposes only. None of the above constitutes medical advice. Always consult a qualified healthcare professional for personal health concerns.

Between Saturdays is a weekly research roundup from Simply Salvia. Four things from science and wellness worth knowing about. If someone sent this to you, you can subscribe here.

Detailed Readings

The Role Temperature Plays in Sleep Quality

Changes in sleeping energy metabolism and thermoregulation during menstrual cycle

Psychodermatology: Bridging Dermatology and Psychiatry

Positive impact of a 10-min walk immediately after glucose intake on postprandial glucose levels

The effectiveness of exercise snacks as a time-efficient treatment for improving cardiometabolic health in adults: a systematic review and meta-analysis

C-Reactive Protein: Clinical Relevance and Interpretation

Part 1 ended at the evidence hierarchy. Which is where most acne content either starts (with a product recommendation) or never gets to at all (because the actual research doesn’t make for exciting content).

Part 2 takes everything from Part 1 and builds it into a routine, a dietary approach, and a cycle-aware protocol that accounts for the weeks that are reliably harder. Not a product list. Not a ten-step routine. A framework based on the research, adapted for what’s actually practical.

4. The Ingredient Guide - What Each Thing Does and When to Use It

5. Diet and Acne - What the Research Actually Supports

6. How to Build a Routine That Actually Works

7. The Hormonal Acne Protocol - What to Do Differently in the Premenstrual Week

8. The Complete Practical Guide

9. Conclusion: The Guide Your Dermatologist Didn’t Have Time to Give You

Read more

Caught My Eye…

Cortisol Peaks When You Wake Up. Your Phone Makes It Worse.

When you wake up, your body produces a surge of cortisol - your highest cortisol output of the entire day. This is called the Cortisol Awakening Response (CAR), and it’s intentional. Cortisol in the morning mobilises blood sugar, activates the immune system, sharpens focus, and prepares you physiologically for the demands of the day. It is the biological equivalent of your body booting up.

This morning cortisol peak is important and healthy. The problem is what happens when you immediately amplify it before your nervous system has had time to regulate it.

Checking your phone within the first few minutes of waking floods your brain with social comparison, unresolved notifications, stressful news, and dopamine-seeking behaviour before your prefrontal cortex (the part of the brain responsible for rational decision-making and emotional regulation) has fully come online. It typically takes 15–30 minutes after waking for the prefrontal cortex to reach full functional capacity. Stimulating the amygdala (the threat and reward detection centre) with a phone screen before that window closes means starting the day in a reactive, slightly elevated-stress state that carries forward.

A 2024 study on morning digital media use found that checking phones within 10 minutes of waking was associated with higher reported stress and more fragmented attention for the remainder of the morning. The mechanism isn’t complicated: cortisol is already at its peak, the nervous system is in a sensitised state, and the phone is an effective cortisol amplifier.

The 30-minute phone-free window after waking isn’t a productivity hack. It’s giving the nervous system the time it needs to land from sleep before being asked to process stimulation. Morning light exposure in that same window, ideally outdoor if possible, has the strongest evidence for anchoring the circadian rhythm, supporting serotonin synthesis, and improving mood and focus for the hours that follow.

The Breakfast Research Has Been Saying This For Years. Most People Are Still Not Doing It.

The most consistent finding in breakfast nutrition research for women is so simple it sounds like it can’t be right: eating 25–30g of protein at breakfast produces better blood sugar control, reduces hunger and cravings for hours, and has measurable effects on what you eat for the rest of the day.

A University of Missouri study found that when women consumed high-protein breakfasts, they maintained significantly better glucose and insulin control than they did with lower-protein or no-protein meals, and the benefit extended beyond breakfast, with improved blood sugar control even after lunch. Research on premenopausal women found that increasing protein at breakfast to 30g reduced daily caloric intake by an average of 441 calories over 12 weeks and produced significant weight loss without any instruction to eat less. Just more protein at breakfast.

The mechanism: protein at breakfast triggers GLP-1 and PYY; the satiety hormones that signal fullness to the brain. These hormones take 15–20 minutes to reach the brain after eating, which is why eating quickly defeats the system. Protein stimulates these hormones more powerfully than carbohydrates or fat. It also stabilises blood sugar in a way that carbohydrate-heavy breakfasts (cereal, toast, pastry, fruit juice) don’t. Setting up stable energy for the morning rather than the blood sugar spike-and-crash that drives the 10am hunger and the need for caffeine to push through it.

The typical British and American breakfast is optimised for the opposite of this: fast, convenient, carbohydrate-heavy, low protein. A bowl of cereal and orange juice starts the day with a blood sugar spike before 8am and a crash by 10am. The tiredness, the craving, the difficulty concentrating mid-morning all of these are very often blood sugar consequences of the first meal, not signs that you need more coffee.

Why You Should Wait 90 Minutes Before Your First Coffee

Caffeine works by blocking adenosine receptors. Adenosine is the compound that accumulates in your brain while you’re awake and produces sleepiness -it’s the biological pressure that builds throughout the day and makes you tired by evening. Caffeine doesn’t remove adenosine. It sits in adenosine’s receptor seats, blocking the signal. When the caffeine clears (after 5–7 hours) the adenosine that accumulated while you were drinking coffee floods back in all at once, often producing the afternoon crash that prompts another coffee.

Here’s the part most people don’t know: adenosine levels are actually at their lowest when you wake up, because sleep cleared most of the previous day’s accumulation. For the first 60–90 minutes after waking, your cortisol peak is handling the alertness that caffeine would normally provide. Drinking coffee in this window isn’t giving your brain something it needs, it’s adding caffeine to a system that’s already running on its own alertness mechanism.

Neuroscientist Dr. Andrew Huberman’s popularisation of the “wait 90 minutes for coffee” protocol has research backing, even if the specific 90-minute number isn’t from a single definitive study. The evidence behind it: cortisol suppresses caffeine’s effectiveness (they both compete for similar arousal pathways), so caffeine consumed during the cortisol peak provides less benefit than caffeine consumed after it. Waiting until cortisol has begun its natural post-peak decline( typically 60–90 minutes after waking) means the caffeine is doing more useful work and the afternoon crash is less severe.

This doesn’t mean no coffee before 90 minutes will ever work. Caffeine still blocks adenosine receptors regardless of timing. But the effectiveness, the dependency curve, and the afternoon crash are all affected by when in the morning you drink it.

Skipping Breakfast Has Different Effects in Women Than Most Research Suggests

Intermittent fasting and time-restricted eating have strong evidence for metabolic health particularly in overweight and metabolically compromised populations. The 16:8 protocol (eating within an 8-hour window, fasting for 16 hours) has consistent research support for blood sugar regulation and weight management.

But there’s a sex-specific dimension that most of the content on intermittent fasting completely ignores. Most of the foundational IF research was conducted in men. Women’s hormonal systems, specifically the hypothalamic-pituitary-ovarian (HPO) axis that governs the menstrual cycle are more sensitive to caloric restriction and meal timing than men’s.

A 2025 review of time-restricted eating in overweight women found meaningful metabolic benefits but also flagged that aggressive fasting windows (over 16 hours) can activate the same stress responses in the HPO axis that underlie hypothalamic amenorrhoea (period loss in response to energy restriction). Cortisol rises with prolonged fasting. Elevated cortisol suppresses GnRH, the hormone that controls the reproductive cycle. In women who are already hormonally sensitive; those with irregular cycles, high stress levels, low body weight, or a history of disordered eating, extended fasting windows can disrupt the cycle.

Research on women specifically found that those who skip breakfast consistently show higher levels of cortisol and more menstrual irregularity than those who eat breakfast. The mechanism: overnight is already a prolonged fasting period, and extending it through skipping breakfast means the body is in a cortisol-driven fasting state well into the morning. For women whose hormonal health is stable and who aren’t showing any cycle disruption, moderate time-restricted eating (12–14 hour windows rather than 16+) appears metabolically beneficial with minimal hormonal risk. For women with irregular cycles, high stress, or hormonal sensitivity, skipping breakfast may not be the right intervention, regardless of its general evidence base.

This isn’t “intermittent fasting is bad for women.” It’s “the research was built on male participants and the female-specific data adds complexity that most fasting content doesn’t acknowledge.”

The information in this post is for educational and informational purposes only. None of the above constitutes medical advice. Always consult a qualified healthcare professional for personal health concerns.

Between Saturdays is a weekly research roundup from Simply Salvia. Four things from science and wellness worth knowing about. If someone sent this to you, you can subscribe here.

Detailed Readings

Morning Light Exposure Affects Cortisol Levels and Stress Response

Protein-packed breakfast prevents body fat gain in overweight teens

Caffeine Science

Understanding Cortisol Hypothalamic Amenorrhea: The Science of Stress

Not the vague “hormones” explanation. Not “you need to drink more water.” The actual mechanism. The biology. The reason certain weeks are reliably worse than others. The reason the cleanser that’s supposed to “clear pores” sometimes makes things worse. The reason the expensive serum did nothing while the cheap tube from the pharmacy did something.

Nobody told me any of it. Not the GP. Not the dermatologist I waited four months to see. And definitely not the TikTok comments.

So this short dive is the explanation I didn’t get at 16. What acne actually is, why your hormones are involved in more ways than you probably realise, what the evidence hierarchy actually looks like for treatment, and the practical guide that puts all of it together.

Let’s start at the beginning.

1. What Acne Actually Is And Why Most People Are Fighting It Wrong

2. Why Your Hormones Are Running the Show — The Menstrual Cycle and Your Skin

3. The Evidence Hierarchy — What the Research Actually Ranks

Chapter 1: What Acne Actually Is And Why Most People Are Fighting It Wrong

The Four-Step Mechanism

Acne isn’t caused by dirty skin. It isn’t caused by not washing your face enough. And it definitely isn’t caused by touching your face. These ideas have been so thoroughly embedded in the way we talk about breakouts that they’ve produced an entire generation of people over-cleansing, over-exfoliating, and stripping their skin barrier in the name of treating acne, which, as I’ll get to, actively makes acne worse.

Here’s what’s actually happening.

Inside each of your pores is a hair follicle with an attached sebaceous gland; a tiny oil-producing structure. Your sebaceous glands produce sebum, which is the oil that keeps your skin lubricated and barrier-protected. This is not a bad thing. Sebum is a normal, necessary part of skin function.

Acne happens when four things go wrong in sequence inside these pores:

Step 1: Too much sebum. The sebaceous gland produces more oil than the follicle can handle. Androgens, specifically dihydrotestosterone (DHT), a form of testosterone, are the main driver of this. More androgen activity means the gland works harder and produces more sebum. This is why acne is so common in puberty (androgens surge), why it’s connected to the menstrual cycle (androgen levels fluctuate relative to estrogen), and why it’s often worse in the premenstrual week.

Step 2: The pore gets blocked. The skin cells that line the inside of the follicle normally shed naturally and exit through the pore. When they don’t, when they build up and stick together instead of exiting they form a plug. This blockage is called a comedo. A comedo that stays closed under the skin is a whitehead. One that opens at the surface and oxidises (turns dark on contact with air) is a blackhead. The dark colour is not dirt. It’s oxidised sebum and skin cells.

Step 3: Bacteria multiply. A bacterium called Cutibacterium acnes (C. acnes) lives on everyone’s skin all the time. It’s part of a healthy skin microbiome. The problem is that C. acnes loves the environment inside a blocked, sebum-filled follicle. It feeds on the sebum, multiplies rapidly, and in doing so breaks down the sebum into free fatty acids that are irritating to the follicle wall.

Step 4: Inflammation. Your immune system detects the bacterial activity and sends inflammatory signals to the area. This is what turns a blocked pore into a red, raised, painful spot. The inflammation can be mild (a small red papule), moderate (a pus-filled pustule), or severe (a deep, painful cyst or nodule that sits under the skin and never comes to a head).

This four-step process — excess sebum, blocked pore, bacterial growth, inflammation, is the foundation of all acne. Understanding it explains why specific treatments work: retinoids target the blocked pore step, benzoyl peroxide targets the bacterial step, anti-inflammatory ingredients and hormonal treatments target the sebum step upstream.

Why Washing Your Face More Makes It Worse

Here’s the part that matters practically: harsh cleansing, over-exfoliation, and stripping products — the instinctive response to oily, broken-out skin, all damage the skin barrier.

A damaged skin barrier makes acne worse in two ways. First, it triggers an inflammatory response that is the same pathway as the inflammatory acne response. Second, it signals the skin to produce more sebum as a compensatory repair mechanism. So stripping your skin makes it oilier and more inflamed which is the exact opposite of what you’re trying to achieve.

A December 2025 review in Molecules covering over 100 acne sources confirmed that maintaining the skin barrier is now considered a critical component of acne management and not just a nice-to-have alongside active treatments.

The correct cleansing approach for acne-prone skin: a gentle, non-foaming or low-foam cleanser, twice a day maximum, that removes surface excess without stripping. That’s it. The work of treating acne happens with the treatments applied after cleansing, not with the cleanser itself.

Chapter 2: Why Your Hormones Are Running the Show — The Menstrual Cycle and Your Skin

This is the chapter that most acne content skips entirely, or covers in one vague sentence about “hormonal acne.” The biology is more specific than that, more interesting than that, and more useful than that because once you understand which hormones do what in which week, the monthly breakout pattern that felt random starts to make complete sense.

The Phase-by-Phase Skin Picture

Your skin contains receptors for estrogen, progesterone, and androgens. Which means every hormonal shift across your cycle is being detected and responded to in your skin and not just in your mood or your sleep.

Week 1 — Menstrual phase: Both estrogen and progesterone are at their lowest. Skin is often in a post-breakout recovery phase. The barrier can be more reactive than usual because prostaglandins (which drive cramping) also affect the skin’s inflammatory state. Sebum production is lower in this phase.

Week 2 — Follicular phase: Estrogen is rising. Estrogen has a genuinely beneficial effect on skin: it supports the skin barrier, promotes collagen synthesis, and critically, reduces sebum production. As estrogen rises through the follicular phase, skin tends to clear and brighten. Many women notice their skin looks best in the week after their period ends. This is why.

Around ovulation: Estrogen peaks, and with it comes the clearest, most luminous skin of the month for many women. But this is also when a brief testosterone surge occurs alongside the LH spike that triggers egg release. For women with more androgen-sensitive sebaceous glands, this can trigger a small breakout right around ovulation even when the rest of the month is clear.

Weeks 3–4 — Luteal phase: This is where things get more complicated. After ovulation, progesterone rises and becomes the dominant hormone. Progesterone stimulates the sebaceous glands to produce more oil. At the same time, as estrogen falls in the late luteal phase, its sebum-suppressing effect disappears. And androgens, still present throughout the cycle become relatively more dominant as estrogen drops.

The result: sebum production peaks in the premenstrual week. The follicular environment is oilier, the conditions for bacterial growth are better, and the inflammatory threshold is lower because the late luteal phase is already a time of heightened systemic inflammation. A 2025 study published in The Journal of Dermatology found that sebum composition changes measurably across the menstrual cycle, with the luteal phase showing the most significant shifts in the lipid profile that drives C. acnes activity.

Approximately 65% of women report worse breakouts in the week before their period. The hormonal explanation is real, documented, and explains exactly why.

Where Hormonal Acne Shows Up and Why

The location of acne breakouts is not random. It’s connected to the density and sensitivity of sebaceous glands in specific areas, and to the hormonal pathways driving them.

Hormonal acne has a signature location: the lower third of the face. Jawline, chin, and the area around the mouth. These are the areas with the highest concentration of androgen-sensitive sebaceous glands aka the glands that respond most to DHT. When androgens drive excess sebum production, this is where it shows up first.

Forehead acne tends to be more connected to skin microbiome disruption, hair products, and barrier issues than to hormones. Cheek acne often has a bacterial, environmental, or friction component (phone screens, pillowcases). Jawline and chin acne that reliably worsens in the week before your period is almost always hormonally driven, which means treating it purely topically, while not addressing the hormonal environment driving it, is treating the symptom rather than the cause.

The Gut-Estrobolome-Jawline Connection

This is the link that’s gaining research attention and that almost no skincare content is discussing yet.

As covered in Between Saturdays, the estrobolome (the collection of gut bacteria responsible for metabolising estrogen) plays a direct role in how much estrogen circulates in the body. When gut microbiome diversity is low, estrogen clearance is impaired. Estrogen that should be processed and excreted stays in circulation longer. Elevated estrogen levels relative to progesterone create a hormonal environment that can worsen acne through several pathways, including by suppressing testosterone-binding proteins, which effectively raises free androgen activity in the skin.

A 2025 review in Dermatology Research and Practice confirmed that the gut-skin axis is now considered a significant factor in acne pathogenesis and that gut microbiome composition is measurably different in people with acne compared to those without it.

This is why for some women, persistent hormonal acne, especially the jawline cystic kind that doesn’t fully respond to topical treatment has a gut health component. The dietary pattern that most consistently supports the estrobolome and reduces the gut-skin inflammatory pathway: high-fibre eating from varied plant sources, fermented foods, reduced ultra-processed food. The same pattern that supports gut health generally.

Chapter 3: The Evidence Hierarchy — What the Research Actually Ranks

This is the chapter where I tell you that most of what wellness TikTok recommends for acne is not at the top of the evidence hierarchy and what actually is.

The American Academy of Dermatology’s 2024 Guidelines

The AAD published updated clinical guidelines for acne management in 2024. These are evidence-based recommendations from the largest body of dermatological research. 18 specific recommendations ranked by strength of evidence. Here’s what got strong recommendations:

Topical retinoids. Strongly recommended. Work at step 2 of the acne mechanism. They accelerate cell turnover so the dead skin cells that form the follicular plug shed properly rather than building up and blocking the pore. They also have anti-inflammatory effects. Tretinoin, adapalene, tazarotene, and trifarotene are all FDA-approved for acne, with no evidence that any one is significantly better than another. Adapalene 0.1% is available over the counter in most countries and is a genuinely effective starting point.

Benzoyl peroxide. Strongly recommended. Works at step 3 — it kills C. acnes bacteria. Notably, it’s one of the only acne treatments that doesn’t create bacterial resistance with extended use (unlike antibiotics). Available at any pharmacy at 2.5–10% concentration. Higher concentration doesn’t mean more effective, it mainly means more irritation. 2.5–5% is where to start.

Topical antibiotics (with BPO). Strongly recommended as part of a combination, never as monotherapy, because antibiotic resistance is a real concern with acne bacteria. Clindamycin combined with benzoyl peroxide has strong evidence. Used alone it’s less effective and risks creating resistant strains.

What got conditional recommendations (real but not the strongest evidence):

Salicylic acid. A beta-hydroxy acid that exfoliates inside the pore. Useful for non-inflammatory, comedonal acne (blackheads and whiteheads). Less effective for inflammatory spots. A good addition but not a first-line treatment for inflammatory acne.

Azelaic acid. Antibacterial and anti-inflammatory, and has the additional benefit of reducing post-inflammatory hyperpigmentation, the dark marks left after spots. Excellent for darker skin tones where PIH is a significant concern. Evidence is real but thinner than for retinoids or BPO.

Niacinamide. Not in the AAD guidelines as a primary acne treatment but has research support for reducing sebum production and skin inflammation. Works as a supporting ingredient rather than a primary treatment.

What Didn’t Make the Evidence Hierarchy

Tea tree oil. Some evidence for mild antibacterial effects, but not at a level that competes with the above. Useful for very mild, occasional breakouts. Not a treatment for inflammatory acne.

Hypochlorous acid. Trending at 132% YoY search growth in 2026. Genuinely useful as it kills C. acnes without creating resistance and is extremely well tolerated by sensitive and compromised skin barriers. But: the acne evidence is thinner than the eczema and wound-healing evidence, and the AAD guidelines don’t include it as a primary treatment. It belongs in a routine, but it’s not doing the heavy lifting.

Natural alternatives generally. Witch hazel, apple cider vinegar, lemon juice, none of these have evidence comparable to the treatments above. Apple cider vinegar and lemon juice can actively damage the skin barrier and should not be applied directly to the face.

Supplements marketed for skin. Zinc has the most interesting acne evidence, it has some anti-inflammatory and antibacterial properties and several studies have found it reduces inflammatory lesion count. But even zinc’s evidence is modest compared to topical retinoids. Supplements sit at the bottom of the evidence hierarchy for acne treatment, not the top.

Why the Evidence Hierarchy Matters

The reason most people cycle through product after product and don’t get consistent results is that they’re investing money and time in ingredients at the bottom of the evidence hierarchy (trendy, gentle, wellness-adjacent) while avoiding or misusing the ingredients at the top (retinoids, BPO) because they’re less aesthetically appealing, require a learning curve, or are just less well marketed.

Adapalene 0.1% costs less than most trendy serums. It has strong evidence behind it. It’s available without a prescription in most countries. The reason it’s not on TikTok every week is that you can’t make it in a pretty bottle with a compelling brand story — the patent expired decades ago.

That’s not a knock on the skincare industry. It’s useful information for where to put your attention and your money.

Part 1 ends here. Part 2 is the practical half. The ingredient guide, the routine, the diet chapter, the hormonal acne protocol, and the phase-by-phase skincare guide for the weeks where breakouts are reliably worse.

Now you know more about what’s actually happening in your skin than most skincare content will ever tell you. You know the four-step mechanism. You know how estrogen, progesterone, and androgens play out across the month and why the premenstrual week is reliably the hardest. You know that the gut microbiome is involved in hormonal acne in a specific way that most people aren’t talking about. And you know what the evidence hierarchy actually looks like, which treatments are strongly recommended, which are conditionally recommended, and which are mostly marketing.

Part 2 is where it becomes a system you can actually use.

Chapter 4 is the ingredient deep dive. How each of the evidence-backed ingredients works, which skin types they suit, and what concentration to start with. Including the honest assessment of hypochlorous acid, azelaic acid, and niacinamide and where they actually belong in a routine.

Chapter 5 is the diet chapter. What the research genuinely supports for acne and skin. The glycaemic index evidence is stronger than most people know. The dairy evidence is more nuanced than most people have been told. The omega-3 finding will probably surprise you.

Chapter 6 is how to build a routine that treats acne without destroying your barrier in the process, because the most common reason acne treatments don’t work is the over-treating that compromises the very barrier you need intact.

Chapter 7 is the hormonal acne protocol. Specific, phase-aware adjustments for the week before your period when the sebum-androgen-inflammation picture is at its most difficult.

Chapter 8 is the complete practical guide: a simple, evidence-based routine from cleanser to SPF, shopping suggestions at different price points, and the signs that mean your acne needs a GP or dermatologist rather than a product change.

Subscribe to read Part 2 →

Sources & Further Reading

Li & Jin. The Mechanism and Research Progress of Skin Microbiota in Pathogenesis of Acne — Dermatology Research and Practice, October 2025

Molecules. Rebalancing the Skin: The Microbiome, Acne Pathogenesis, and the Future of Natural and Synthetic Therapies — December 2025

MDPI Biomolecules. The Evolving Microbial Paradigm in Acne — March 2026

Lau et al. Physiological Differences in Sebum Composition in Regularly Menstruating Healthy Women — Journal of Dermatology, August 2025

Menstrual cycle phases and acne flares — ScienceDirect, September 2025

Healthline. Period acne guide — updated January 2026

AAD Guidelines of care for the management of acne vulgaris — JAAD, January 2024

Taha & Shakhshir. The mediterranean diet and acne vulgaris: systematic review and meta-analysis — Nutrition & Metabolism, November 2025

Systematic review: low glycaemic load diets and acne, 2025

Khanna et al. Effects of diet on acne and its response to treatment — American Journal of Clinical Dermatology

Löffler et al. Deficit of omega-3 fatty acids in acne patients — PMC, 2024

La Belle Vie. Acne treatment trends 2026 — hypochlorous acid and emerging ingredients

Skin Science Hub. Hypochlorous acid for skin — December 2025

Caught My Eye…

Berberine Is Not “Nature’s Ozempic”. A March 2026 Review Finally Said It Directly.

Berberine has had 100 million+ TikTok views as a natural alternative to Ozempic. The claim: it works on the same pathways, produces the same appetite suppression, and gives you the weight loss results of semaglutide without the prescription or the side effects.

A review published in the International Journal of Molecular Sciences in December 2025, summarised by Medical Xpress in March 2026, looked at this claim carefully and reached a clear conclusion: the comparison is an oversimplification that doesn’t reflect how berberine actually works, or how strong the evidence is.

Here’s the honest picture. Berberine is a plant compound that activates an enzyme called AMPK, which plays a role in regulating metabolism and improving insulin sensitivity. It does have genuine evidence for lowering blood sugar particularly in people with type 2 diabetes and some modest evidence for supporting weight loss over 8–12 weeks. These are real effects.

But Ozempic (semaglutide) is a GLP-1 receptor agonist. It directly mimics a gut hormone that tells your brain you’re full, dramatically suppresses appetite, slows gastric emptying, and produces an average weight loss of 15–20% of body weight in clinical trials. Berberine does not work through the GLP-1 pathway. It doesn’t suppress appetite in the same way. It doesn’t produce remotely comparable weight loss outcomes. The mechanisms are different, the effect sizes are different, and the evidence base is different.

What the March 2026 review specifically found: responses to berberine differ widely between individuals likely because its effects run through the gut microbiome, which varies enormously between people. One person’s berberine response is completely different from another’s in a way that doesn’t happen with semaglutide. The individualised, microbiome-dependent mechanism is interesting and worth more research. It is not the same mechanism as Ozempic.

What berberine does have evidence for: modest blood sugar reduction, some support for insulin sensitivity, potential gut microbiome benefits. What it doesn’t have evidence for: appetite suppression comparable to GLP-1 drugs, significant weight loss as a standalone intervention, long-term safety beyond 3–6 months.

If you’re taking it: the evidence doesn’t suggest it’s harmful at standard doses (500mg 2–3x daily) for most healthy adults. The evidence does suggest the “natural Ozempic” framing is marketing, not science. And there are specific groups who should avoid it entirely: pregnant or breastfeeding women, people on blood sugar or blood pressure medication, and people with clotting disorders.

Microplastics Are In Your Ovarian Follicular Fluid. Here’s What the Research Actually Says.

This is the one that wellness content gets very wrong in two opposite directions: either “microplastics are fine, the danger is overhyped” or “microplastics are destroying your hormones and fertility right now.” The actual research sits in a more specific and more unsettling place than either of those.

A systematic review published in Archives of Gynecology and Obstetrics in January 2025, covering 15 experimental studies, found that microplastic exposure significantly affects ovarian function, decreases fertility rates, and disrupts hormone levels in female subjects. A separate review in the International Journal of Gynecology & Obstetrics in October 2025 confirmed the pattern: microplastics and nanoplastics interfere with the hypothalamic-pituitary-ovarian axis (the hormonal control system that regulates the menstrual cycle) in ways that disrupt estrogen and progesterone production.

The most striking single finding: researchers detected microplastics inside human ovarian follicular fluid. The fluid that surrounds developing eggs. This means microplastics are reaching the immediate environment of egg development. The clinical implications of this aren’t fully established yet. But the fact that they’re present is not a small finding.

A meta-analysis published in August 2025 found that consuming food in plastic containers significantly increased microplastic contamination in pregnant women, and that microplastic content in the placenta correlated with worse pregnancy outcomes including intrauterine growth restriction.

The honest caveats: most of the reproductive health studies are in animals (mice, zebrafish, rats), not humans. Human studies exist but are fewer and typically smaller. The dose-response relationship (how much exposure is needed to produce harm) isn’t fully established. “Microplastics are present” is confirmed. “Microplastics are causing X level of harm in healthy women in their 20s” is still being quantified.

What this means practically - not catastrophically, but concretely:

These aren’t reasons for anxiety. They’re reasons for easy, low-effort swaps that reduce the highest-dose exposures while the research catches up.

The Vagus Nerve Trend Has Something Real To It. The Devices Being Sold Around It Have More Confidence Than Evidence.

Vagus nerve stimulation has gone from a clinical procedure for treatment-resistant epilepsy and depression to a TikTok wellness aesthetic involving ear seeds, special breathing devices, cold plunges, and $400 gadgets - in approximately 18 months.

The biology is real. The vagus nerve is the longest nerve in the body, running from the brainstem through the heart, lungs, and gut. It’s the primary conduit of the parasympathetic nervous system; the “rest and digest” counterpart to the “fight or flight” sympathetic system. Stimulating it activates anti-inflammatory pathways, slows heart rate, reduces cortisol output, and shifts the nervous system toward calm. A 2026 comprehensive review in Comprehensive Physiology confirmed that vagus nerve stimulation affects the brain’s arousal, emotion, and homeostatic networks through direct anatomical pathways.

The clinical evidence for implanted vagus nerve stimulators (for epilepsy, treatment-resistant depression, and PTSD) is solid. For non-invasive transcutaneous auricular VNS (taVNS), stimulating the vagus nerve through the ear, the evidence is growing and genuinely interesting. A 2025 placebo-controlled trial found significant reductions in stress, cognitive anxiety, and somatic anxiety with auricular VNS. A 2025 systematic review found non-invasive VNS significantly improved symptoms across gut disorders including IBS and inflammatory bowel disease. A 2022 trial found 50% improvement in self-reported sleep quality after one month.

The honest state of the evidence: non-invasive VNS shows real promise. Most studies are small. Effect sizes vary considerably between individuals. The consumer devices being sold, ranging from electrical ear clips to vibrating neck devices, are not the same as the devices used in clinical trials, and their efficacy hasn’t been independently validated. “The vagus nerve is real and stimulating it does things” is confirmed. “This £200 device will regulate your nervous system” is a different claim with much weaker evidence.

What does have good evidence for improving vagal tone without a device:

Sleepmaxxing: What the Trend Gets Right, and the One Thing It Gets Wrong

Sleepmaxxing - the Gen Z TikTok movement to optimise sleep through supplements, devices, and routines, has been described by the director of UC Berkeley’s sleep centre as Gen Z “reclaiming their right to a full night of sleep without embarrassment.” Which is genuinely good.

The things sleepmaxxing gets right:

The thing the trend gets wrong: the assumption that more optimisation tools equals better sleep. Mouth taping (covered in an earlier Between Saturdays; the 2025 PLOS One systematic review found it can be dangerous for people who mouth breathe due to obstruction, which is most people who mouth breathe). Sleep tracking devices creating anxiety about sleep scores - a documented phenomenon researchers now call “orthosomnia,” where sleep tracking itself causes sleep anxiety that worsens sleep quality. Stacking multiple supplements (magnesium + melatonin + L-theanine + ashwagandha + glycine) without understanding what each does and whether the combination makes sense. And taking magnesium, which does have good evidence for sleep quality, in the wrong form (magnesium oxide, the cheapest and most common, has the lowest bioavailability for neurological effects).

The sleepmaxxing principle is right. Sleep is the most foundational health intervention available and the most consistently undervalued. The one well-evidenced, accessible intervention that most people can add without any device or supplement: a consistent wake time, maintained even on weekends. Sleep research consistently finds that irregular sleep timing (varying by more than 60 minutes between weekdays and weekends) has measurable negative effects on metabolism, mood, and cognitive function - independent of total sleep hours. The sleep schedule is more powerful than the sleep gadget.

The information in this post is for educational and informational purposes only. None of the above constitutes medical advice. Always consult a qualified healthcare professional for personal health concerns.

Between Saturdays is a weekly research roundup from Simply Salvia. Four things from science and wellness worth knowing about. If someone sent this to you, you can subscribe here.

Detailed Readings

What to know about berberine, the so-called “nature’s Ozempic”

Impact of microplastics on female reproductive health: insights from animal and human experimental studies: a systematic review

A review of the impact of micro‐ and nanoplastics on female reproduction

A Review of Vagus Nerve Stimulation for Disease: Comprehensive Theory and Evidence for Mechanisms of Action

The Effects of Vagus Nerve Stimulation on Stress, Competitive Anxiety, and Depression in Elite Shooters

Caught My Eye…

Why Your 20s and 30s Are the Most Metabolically Important Decade of Your Life

This is not a scare story. It’s a reframe that the research supports and that almost no mainstream health content communicates properly.

Peak bone density is reached somewhere between the ages of 25 and 30. After that point, bone density can be maintained and protected, but it can’t be significantly increased. The bone density you build during your teens and twenties is what you’ll be drawing on for the rest of your life. Women who enter their 40s and 50s with higher bone density have a measurably lower risk of osteoporosis, fractures, and the cascade of health complications that follow, particularly after menopause, when estrogen decline accelerates bone loss.

Peak muscle mass follows a similar trajectory, peaking in the early 30s and declining gradually from around 35 onwards unless active resistance training maintains it. The Frontiers in Endocrinology January 2026 study I covered in the weight loss Short Dive confirmed that resistance training is the single most effective strategy for preserving lean muscle during a calorie deficit, but the same principle applies beyond dieting. Muscle built now is metabolic capital. It raises your resting metabolic rate, supports blood sugar regulation, protects joints, and is the most reliable predictor of independence and physical function in later life.

The 2026 women’s health trends report from Mira noted that women aged 25–30 are now the most active health trackers, and cited a growing research consensus that the habits built in your 20s and 30s become your biological reserves for your 50s and 60s. Muscle mass, bone density, cardiovascular fitness, metabolic health, gut microbiome diversity — all of these peak and plateau in early adulthood, and the maintenance trajectory from there depends heavily on the habits already in place.

What the practical version looks like: resistance training started in your 20s or early 30s is not just fitness. It’s bone and muscle maintenance that will matter more in 20 years than it does now. Adequate calcium and vitamin D during this same window supports the bone mineralisation that peaks before 30 and can’t be fully recaptured afterwards. The baseline tests worth considering in your 20s to early 30s: AMH (ovarian reserve, if fertility planning is relevant), a DEXA scan if bone density is a concern (family history, history of hormonal disruption or very low body weight), full metabolic and hormone panel, and vitamin D levels.

None of this is about anxiety. It’s about using information. The research on longevity is consistent on one point: the time to build the reserves is before you need them, not after.

You’re Probably Not Applying Enough Sunscreen. The Research on How Much Is More Specific Than You Think.

Most people who wear SPF daily are wearing significantly less than the amount the SPF rating was tested at. This is not a minor discrepancy. It changes the protection level in a meaningful way.

SPF ratings are calculated at a standard application density of 2mg per square centimetre of skin. For the face alone, this translates to approximately a quarter teaspoon (roughly 1.25ml) of SPF product. Research has consistently found that most people apply somewhere between a quarter and half of this amount in their actual daily routine, which means an SPF 50 product is effectively delivering somewhere between SPF 10 and SPF 25 in real-world conditions.

The implication is simple: if you’re wearing SPF 30 and applying about half the recommended amount, you’re getting approximately SPF 9–12. If your concern is photoageing (UV-driven collagen breakdown, hyperpigmentation, uneven texture) or skin cancer prevention, the application amount matters as much as the SPF number.

The practical guidance from dermatology research: a shot-glass amount (approximately 30ml) for the whole body when in a swimsuit. For the face, a nickel-sized amount, more than most people use. Two finger lengths of product from two fingers placed together (the “two-finger rule”) is a commonly cited estimate for face and neck combined.

Reapplication also matters more than most SPF content acknowledges. SPF degrades with UV exposure, sweating, and time. The standard guidance is reapplication every two hours in direct sun, or after swimming or heavy sweating. A morning application of SPF for a day spent mostly inside doesn’t require reapplication. A morning application for a day that includes extended outdoor time, a lunch break in the sun, or outdoor exercise does.

The SPF type matters less than application consistency and amount. A well-applied SPF 30 beats a poorly applied SPF 50 every time. The more important variables are: physical (mineral) or chemical filter based on your skin type and preference, broad-spectrum coverage (both UVA and UVB), and a texture you’ll actually use every day.

Rest Is Not the Opposite of Progress. The Research on Recovery Makes This Concrete.

The fitness and productivity culture version of health has a rest problem. Rest is framed as a necessary evil. The minimum required recovery before you can train again, the time when nothing useful is happening. The research says something different.

Here’s what is actually happening during rest and sleep after exercise:

The muscle tissue that was stressed during training is being repaired and reinforced by satellite cells (muscle stem cells). This process requires growth hormone, which, as the UC Berkeley research covered above shows, is primarily released during deep non-REM sleep. Without adequate sleep after training, the repair signal is dampened and the adaptation is incomplete.

Cortisol, the stress hormone that rises during intense training, is cleared during sleep. When the next training session happens before cortisol from the previous one has fully cleared, because recovery time was too short or sleep was too disrupted, cortisol accumulates. Chronically elevated cortisol promotes muscle breakdown (catabolism) rather than muscle building (anabolism), drives fat storage, and reduces the training adaptation you were working for.

Glycogen (the stored form of carbohydrate that powers high-intensity exercise) is replenished during rest, primarily through dietary carbohydrates eaten after exercise. Without adequate carbohydrates post-training and adequate rest time, glycogen stores remain depleted. The next training session starts at a lower energy substrate than the previous one. Performance declines, fatigue compounds, and the body starts pulling energy from muscle protein rather than stored fat, the opposite of what most training programmes are designed to produce.

The research on overtraining syndrome (the documented condition that occurs when training volume exceeds recovery capacity) finds that its primary symptoms are declining performance, persistent fatigue, disrupted sleep, elevated resting heart rate, and increased injury risk. These are the same symptoms that, in women, are also associated with low energy availability (not eating enough to support training volume) a well-documented condition in female athletes that suppresses the hormonal cycle and, in its more severe form, leads to bone stress injuries.

The practical version: rest days are not days when nothing is happening. They are days when the adaptation you trained for is actually occurring. The minimum effective dose of training for health and body composition is 2–3 resistance sessions per week. Adding more sessions without proportionally increasing recovery; sleep, nutrition, rest days does not produce proportionally better results. It produces overtraining.

For women specifically: in the late luteal phase, when sleep is already more fragmented and the nervous system is already more reactive, recovery from the same training stimulus takes longer. Protecting sleep, reducing evening training intensity, and not interpreting reduced capacity in this window as weakness are all evidence-informed responses to a documented physiological reality.

The Stress-Skin Feedback Loop, And the One Thing That Breaks It

I’ve covered the cortisol face content in the Short Dives. This is a specific addition to that picture that came from more recent research and is worth its own paragraph.

The relationship between stress and skin isn’t one-directional. Stress worsens skin through the cortisol mechanism; barrier disruption, increased sebum, impaired overnight repair. But skin conditions themselves then produce stress, which produces more cortisol, which worsens the skin condition further. Research has documented this bidirectional feedback loop in acne, eczema, and rosacea specifically, conditions where flares both cause and are caused by psychological stress, creating a cycle that’s genuinely difficult to break purely through topical intervention.

The finding that matters: a 2025 study specifically examining skin-related quality of life and stress found that psychological interventions, specifically cognitive behavioural therapy and mindfulness-based stress reduction produced measurable improvements in inflammatory skin conditions independent of topical treatment. This isn’t “your skin problem is in your head.” It’s that the HPA axis (the stress response system) is a direct regulator of skin inflammation, and interventions that reduce HPA activation produce skin improvements through that pathway.

The practical implication for anyone dealing with stress-driven skin: topical treatment matters and is worth doing properly. But if your skin consistently flares during high-stress periods and doesn’t fully respond to topical approaches, the HPA axis is likely a maintaining factor. Sleep, which is the most powerful cortisol regulator with the most evidence, is the intervention with the clearest mechanism for this specific pattern. Even single-night sleep deprivation measurably elevates cortisol and inflammatory markers and multiple consecutive nights of poor sleep drives the chronic cortisol elevation that makes stress-driven skin conditions persistent rather than episodic.

The information in this post is for educational and informational purposes only. None of the above constitutes medical advice. Always consult a qualified healthcare professional for personal health concerns.

Between Saturdays is a weekly research roundup from Simply Salvia. Four things from science and wellness worth knowing about. If someone sent this to you, you can subscribe here.

Detailed Readings:

Resistance training as a key strategy for high-quality weight loss in men and women

Mira’s Women Heath Trends Report: 6 Trends Reshaping 2026 and Beyond

How Much Sunscreen Are We Really Getting?

Why Does Sunscreen Only Last 2 Hours?

Scale-Free and Multifractal Time Dynamics of fMRI Signals during Rest and Task

Cortisol rises during intense workouts. Is that really a bad thing?

What is psychodermatology?

The Skin–Brain–Exposome Axis in Stress-Sensitive Dermatoses: A Narrative Review

Microbiome-Skin Axis in 2026