So That's Why

Nearly all of us blame the calendar for wrinkles, but the science says the calendar is mostly innocent. Estimates put at least 80% of visible facial ageing down to sun exposure, not birthdays. In this episode, Jen, Chris and Matt go one layer beneath the surface of the skin to find out what a wrinkle actually is. They cover the slow collagen decline that starts in the late twenties, the fibroblasts that build the skin's scaffolding, and the MMP enzymes that break it down again. They explain how UV light manages to speed up demolition and quieten repair in a single move, why not all wrinkles are the same thing, and the sharp collagen drop that arrives around menopause. There is also a straight answer on collagen drinks, and the cheap, unglamorous product that outperformed everything else in a four-year controlled trial. Key Point Timestamps 00:04 The question and the 80% figure 01:51 The collagen timeline, decade by decade 03:15 Collagen, elastin, fibroblasts and MMPs 08:18 How sunlight causes most of what we see 10:06 Dynamic, static and sleep wrinkles 12:22 What the evidence says about collagen supplements 14:28 SPF, retinoids and vitamin C 18:02 Injectables, lasers and the lifestyle stuff Wrinkles Form in a Layer You Cannot See (03:15) Wrinkles do not start in the visible surface of the skin. They form in the dermis underneath, where three things do the structural work. Collagen provides firmness and tensile strength, elastin lets skin stretch and spring back, and hyaluronic acid holds water and keeps the layers plump. All three are made and maintained by one type of cell, the fibroblast. In young skin, fibroblasts lay down fresh collagen and elastin about as fast as the old material wears out. Two things change that with age. A growing share of fibroblasts become senescent, meaning they largely stop producing and start giving off low-level inflammatory signals. At the same time, a family of enzymes called MMPs becomes more active. Their normal job is useful, clearing out worn collagen so fresh collagen can replace it, but the balance tips. "Collagen and elastin get broken down and disorganised faster than the fibroblasts rebuild them." — Chris Sunlight Speeds Up Breakdown and Slows Repair (08:18) When ultraviolet light hits the skin, it generates a burst of unstable molecules called free radicals. Within minutes, those free radicals switch on the MMPs, the very enzymes that break collagen down. Each unprotected sunny hour becomes a small spike of collagen loss. Then it does a second thing simultaneously. It quietens the signal that tells fibroblasts to make new collagen. That is why sunlight accounts for so much of what shows up on skin. It is not vague damage. It drives both ends of the same process, and the effect is cumulative rather than dramatic. "The sun isn't ageing our skin in some vague way, it seems to be driving the two exact processes you've both just described at both ends, which kind of makes it feel less like fate and something that we can actually deal with." — Matt The Collagen Drop Nobody Talks About Enough (10:06) Individual variation matters enormously here. How much protective pigment skin produces is largely down to genetics, and that pigment strongly affects how much UV gets through in the first place. Hormones matter too, and this part is badly under-discussed. Around menopause, as oestrogen falls, women can lose up to about 30% of their skin's collagen in roughly the first five years. By the age of 50, nearly 50% can be gone. Set against the background rate of one to 1.5% a year, that is a very different order of change arriving in a very short window. The Cheapest Bottle in the Shop Wins (14:28) For collagen drinks and powders, a recent pooled analysis of 23 peer-reviewed trials found the strongest independent studies do not show a clear effect on wrinkles or elasticity. The gut cannot absorb collagen whole, so it breaks it into amino acids first. What does have strong evidence is considerably less exciting. In a well-known controlled trial, people using a daily broad-spectrum sunscreen showed no measurable increase in skin ageing over four years, while the comparison group aged visibly. Retinoids and topical vitamin C form the next tier down. "The cheapest and most ignored bottle in the shop beats the 40 quid miracle serum sitting right next to it." — Matt "It's never too late to start, because you're always preventing the next decade of damage even if you can't undo the last one." — Jen About So That's Why So That's Why is a weekly podcast where Jen, Chris and Matt unpack the science behind everyday health questions. No jargon, no judgment, just genuine curiosity and proper research. Website: https://www.vegetology.com/so-thats-why-podcast

Your metabolism has an alibi. A study of over 6,000 people found metabolic rate is essentially flat from 20 to 60. Most of us start blaming our metabolism somewhere in our thirties. The largest study ever done on human energy expenditure suggests we have been accusing the wrong party. Using doubly labelled water, the gold standard for measuring energy expenditure in real life, researchers tracked over 6,000 people aged from eight days old to 95 across 29 countries. Between 20 and 60, metabolic rate holds steady. No dip in the thirties, no crash in the forties, and no measurable effect of pregnancy or menopause once size and body composition are accounted for. A real decline does arrive after 60, at around 0.7% a year, and Jen, Chris and Matt unpack the five things driving it. They also cover what actually holds it off, from resistance training and protein targets to where creatine, caffeine and green tea genuinely sit in the evidence. Chapters 00:00 Why we all blame our metabolism 00:54 What the biggest study on energy expenditure found 04:58 So why do we gain weight in midlife 07:03 The five things that change after 60 13:07 Resistance training at any age 14:14 The protein numbers that have shifted 16:55 Creatine, aerobic activity, caffeine and green tea 22:07 The verdict on metabolism and age Metabolic Rate Is Flat From 20 to 60 (00:54) The doubly labelled water technique tracks heavy forms of hydrogen and oxygen as they leave the body, which tells researchers how much CO2 someone is producing and therefore how much energy they are burning. Crucially, it measures ordinary life rather than a treadmill test. Over 6,000 participants, aged eight days to 95, across 29 countries Energy expenditure peaks at around eight or nine months old, when babies burn roughly 50% faster than an adult relative to body size The rate settles at around 20 and then stays flat for four decades "You've been blaming an innocent party, so it's like accusing a housemate who moved out years ago of finishing all the biscuits." Jen Why Midlife Weight Gain Happens Anyway (04:58) If the rate is flat, the weight gain needs another explanation. Tom Sanders, professor of nutrition at King's College London, said findings like these support the view that rising obesity is driven by excess energy intake rather than falling energy expenditure. Alongside that, muscle mass tends to fall, and a body with less muscle burns less energy in total. "So your machinery isn't getting worse with age. There may simply be less of the expensive machinery in your body." Jen The Five Things That Change After 60 (07:03) After 60, total energy expenditure falls by around 0.7% a year, which reaches roughly 26% lower by the age of 90. Five mechanisms run at once. Sarcopenia. Inactive adults can lose 3 to 5% of their muscle per decade from their thirties. Muscle is metabolically active tissue, so it costs energy even at rest. Jen compares it to the standing charge on an energy bill, the bit you pay whether or not you switch anything on. Mitochondria. Mitochondrial DNA accumulates mutations and oxidative damage, so ATP production becomes less efficient. Mitophagy, the process that clears out damaged mitochondria, also slows. Hormones. Growth hormone, IGF-1 and testosterone decline alongside changes in thyroid function and insulin sensitivity. Reduced output per kilo. The remaining tissue does less per kilogram than it used to. Anabolic resistance. Ageing muscle responds less strongly to protein and to being used. "So it's wear and tear, plus the maintenance team that's also slowing down." Matt What Actually Holds It Off (13:07) Resistance training is the single most evidence-backed intervention because it targets the biggest modifiable driver. Muscle protein synthesis machinery stays responsive to training into very old age, so there is no point at which starting stops being worthwhile. Protein targets for older adults now sit at roughly 1 to 1.2 grams per kilogram of body weight, rising to 1.2 to 1.5 for those training Around 25 to 40 grams of good quality protein per sitting, spread across three meals, does more than one large evening portion A 2025 systematic review and meta-analysis found creatine plus resistance training improved lower limb strength and lean muscle mass more than training alone Caffeine and green tea have real but small and short-lived effects If you have kidney disease or are on a medically restricted diet, protein targets are a conversation for your doctor "Keep the muscle you've got and feed it properly. Your body stays responsive to training and diet far longer into life than people assume." Chris About So That's Why So That's Why is a weekly podcast where Jen, Chris and Matt unpack the science behind everyday health questions. No jargon, no judgment, just genuine curiosity and proper research. Website: https://www.vegetology.com/so-thats-why-podcast

Two people, the same beach, the same sun. One turns golden, the other turns red. Why? That is the question Jen, Chris and Jamie set out to answer this week, and the answer surprises almost everyone. Tanning isn't a skill you build over a summer. Whether you can tan at all is settled by your genes, and it was decided before you were born. The team unpack what a tan really is (a repair job, not a sign of health), why everyone has roughly the same number of pigment cells but wildly different results, and the two pigments that decide whether you go bronze or go pink. Along the way they bust the base tan myth, put sunbeds firmly in their place, and explain why the person who moves abroad and looks "permanently tanned" is actually showing years of damage. Chris, a formulation scientist who has spent decades working in sun protection, also lays out what genuinely protects your skin. Key Point timestamps: 00:34 What a tan actually is 06:59 Why some people tan and others only burn 10:50 The Fitzpatrick scale and what it means 13:18 What actually protects you (and the truth about sunbeds) (Timestamps are based on the transcript section markers and should be verified against the final edit.) A Tan Is a Repair Job, Not a Sign of Health (02:34) Whatever your skin tone, you carry roughly the same density of pigment-making cells, about 1,200 per square millimetre. The pigment they make is melanin, the skin's own sunscreen. The catch is that skin doesn't make more melanin because the sun is good for it. It makes more because ultraviolet light has already caused damage. UVB harms a skin cell, a protein called p53 (nicknamed the guardian of the genome) raises the alarm, and that signal tells your pigment cells to start producing melanin. The damage always comes first. "A tan is a repair job. It's not a glow of good health." (Chris) Why Some People Tan and Others Only Burn (06:59) There isn't one melanin; there are two. Eumelanin is the dark, more protective pigment that absorbs and safely disperses UV. Pheomelanin is the reddish one that offers little protection and can even trigger oxidative stress. Chris compares your pigment cells to little printing shops. The question was never how many you have, since everyone has about the same number. It's which melanin cartridges are loaded inside them, and that is largely genetic. Around 1 in 20 people, the classic redheads, make almost entirely pheomelanin and barely any eumelanin, so they burn and freckle however careful they are. The Fitzpatrick Scale and What It Means (10:50) Dermatologists grade skin from 1 to 6 on how readily it burns and tans, using the Fitzpatrick scale, developed in the 1970s. Even the darkest, type 6 skin offers natural protection roughly equivalent to an SPF of only 10 to 13, and that is a rough comparison. Every skin type can still burn and be damaged. An older version of the scale wrongly suggested darker skin was safe, and that myth causes real harm because skin cancers can get spotted later. "So it's protection that turns up late and leaves early." (Jamie) What Actually Protects You (and the Truth About Sunbeds) (13:18) If the tan isn't doing the protecting, something else has to. Chris recommends a broad-spectrum sunscreen (covering UVA and UVB) at SPF 25 or higher, reapplied through the day, plus clothing, shade and avoiding the midday sun. Sunbeds are not a gentler option. They deliver very concentrated UV, most of the damage is invisible, and starting young sharply raises the risk of serious skin cancer. And the pale person who moves somewhere sunny and looks bronzed years later? That is accumulated UV injury, not a built-up tan. "There's no such thing as a safe tan, and you sadly can't train your skin into making one either." (Jen) About So That's Why So That's Why is a weekly podcast where Jen, Chris and Matt unpack the science behind everyday health questions. No jargon, no judgment, just genuine curiosity and proper research. Website: https://www.vegetology.com/so-thats-why-podcast

Cortisol has become the hormone everyone wants to get rid of. It is also one of the reasons you can get out of bed at all. Jen, Chris and Matt unpack what cortisol is actually doing while you go about your day. They cover how the HPA axis works as a self-correcting chain rather than a tap left running, why cortisol climbs before you wake and jumps again in the first half hour after you open your eyes, and how one hormone reaches nearly every tissue in the body by slipping into the nucleus of your cells and changing which genes are switched on. They also look at where the frightening reputation genuinely comes from. Chronic elevation is a real problem, the cortisol belly has more behind it than you might expect, and a flattened daily rhythm is one of the most consistent biological findings in depression. Adrenal fatigue, on the other hand, is not a recognised diagnosis. In this episode 00:00 Introduction 01:13 What cortisol actually is 02:49 How your body decides how much you get 04:10 The daily rhythm and the cortisol awakening response 08:46 When cortisol goes wrong 11:09 Adrenal fatigue and the myths the internet loves 14:54 What actually helps 19:03 Well-timed cortisol, not low cortisol Cortisol Is Talking to Almost Every Cell You Own (01:13) Cortisol is a glucocorticoid, a steroid hormone built from cholesterol by the adrenal glands that sit on top of your kidneys. Nearly every tissue in the body carries glucocorticoid receptors, the docking sites cortisol uses to pass instructions into a cell. The reason its reach is so wide comes down to one property. Cortisol is fat soluble, so it slips straight through the cell membrane and into the nucleus, where it changes which genes are switched on. "So it's not tucked away doing one small job then, it's talking to more or less all of me at the same time." Matt The System Was Built to Turn Itself Down (02:49) The HPA axis is a three-part chain. The hypothalamus releases CRH, which tells the pituitary to release ACTH, which tells the adrenals to release cortisol. Once cortisol rises, it signals back up the chain and tells the top to ease off. "It's not a tap left running. It turns itself down once the messages seem to have landed." Matt Almost everything that goes wrong with cortisol is a version of that tap failing to turn itself down. Cortisol Clocks On Before You Do (04:10) Cortisol runs highest in the early morning and lowest around midnight. On top of that sits the cortisol awakening response, named by the Endocrine Society. In the first half hour after waking, cortisol jumps a further 38 to 75 per cent on top of the level it was already climbing to, in roughly 77 per cent of people. That rise is not a side effect of waking up. It is part of the signal that wakes you, and current thinking is that it is anticipatory. The jump tends to be bigger before a workday and it goes flat in burnout. "So the snooze button then is me arguing with my own biology, and it seems losing." Matt Adrenal Fatigue Is Not the Problem to Solve (11:09) Adrenal fatigue, the idea that the glands get exhausted and stop making cortisol, is not a recognised diagnosis and the evidence does not support it. What is real is HPA axis dysregulation, where the signalling between brain and glands drifts out of rhythm. "The glands aren't worn out, the timing's off, and that's a very different thing to put right." Chris The team are also clear that a genuine cortisol problem is a blood test and a conversation with a doctor, not a hunch from an internet forum. And on supplements, they are upfront. Vegetology sells them, and for cortisol specifically the evidence is thin. What Actually Helps (14:54) Sleep is the single strongest regulator of the rhythm, by a wide margin. Gentle to moderate movement nudges the baseline down over time, while constant over-training keeps cortisol stuck high. A sharp blood sugar crash is one of the strongest triggers there is for a cortisol spike, so regular meals with a bit of protein help. Easing back on the big afternoon coffee and late alcohol helps the evening dip arrive on time. "You were never meant to have low cortisol, you're meant to have well-timed cortisol." Jen About So That's Why So That's Why is a weekly podcast where Jen, Chris and Matt unpack the science behind everyday health questions. No jargon, no judgment, just genuine curiosity and proper research. Website: https://www.vegetology.com/so-thats-why-podcast

A cold shower, a jump scare and your favourite song all trigger the same reflex. Here's why we get goosebumps, and what they really mean. This week, Jen, Chris and Jamie unpack one of the body's quietest mysteries. Why does a freezing shower, a fright in a dark room and the best moment of a song you love all produce the exact same reaction? The answer starts with a single nervous-system circuit and a tiny muscle at the base of every hair. Along the way, the team explores why goosebumps are far more common than most people assume, the surprising 2020 finding that links the reflex to hair growth, why some people get musical chills and others never do, and a neat myth-bust: most of the goosebumps you think you feel never actually reach your skin. There's a rare superpower, a gentle wellbeing footnote, and Chris's obligatory Captain Sensible moment. In this episode: (01:44) How common goosebumps really are (03:42) The biology behind the bumps (05:52) Where the reflex comes from (08:20) Frisson and why music gives you chills (10:17) Why the shiver and the bump are not the same thing (12:21) What goosebumps say about you Goosebumps Are a Whole-Body Reaction, Not Just Your Hair (03:42) Almost every hair on your body has a tiny muscle at its base called the arrector pili muscle. When it contracts, it tugs the hair upright and pulls the skin into a little dome. Across a whole patch of skin, that gives you the pebbled look named after a plucked goose. The trigger is the sympathetic nervous system, the same side of you that runs fight-or-flight, with noradrenaline carrying the message. For almost everyone, it is completely involuntary. "Picture it less like an alarm and more like an orchestra following the same conductor." (Chris) "Goosebumps are simply the part of the performance that you actually see." (Jen) The Reflex Has a Surprising Second Job (06:55) Goosebumps are not the do-nothing quirk people assume. A 2020 study found that the nerves setting off goosebumps sit right next to the stem cells in your hair follicles. A brief burst of cold gives you the bumps. Prolonged cold can nudge those same nerves into helping the follicle grow new hair. It is still fresh research, but it suggests the reflex is doing quiet maintenance work most of us never knew about. Frisson Explains Why Music Gives You Chills (08:20) The musical version of goosebumps has its own name: frisson. Your emotional brain flags a sudden swell in the music as a possible big event and fires the response. Then the rest of your brain catches up, confirms you are safe, and rewards you with a hit of dopamine. Estimates suggest anywhere from 45% to 85% of people get musical chills, and it turns out to be less about being emotional and more about how actively you engage with what you are hearing. "So it's basically a jump scare with a happy ending." (Jamie) The Shiver and the Bump Are Not the Same Thing (10:17) Here's the myth-bust. When researchers use skin sensors to measure the real muscle response, only about a third of the goosebumps people report actually show up on the skin. The shivery chill you feel and the physical contraction are two separate events. They often travel together, but they don't have to. "So most of the time that I think I've got goosebumps, I haven't actually got goosebumps. It's my brain telling me I've got goosebumps." (Jamie) About So That's Why So That's Why is a weekly podcast where Jen, Chris and Matt unpack the science behind everyday health questions. No jargon, no judgment, just genuine curiosity and proper research. Website: https://www.vegetology.com/so-thats-why-podcast