Steven Bartlett

True: the brain consumes around twenty percent of your energy, and that metabolism produces heat, which is dissipated mainly through the bloodstream.

True: research on infants shows that humans develop expectations about how objects behave very early on, before they could have learned this. This core knowledge is considered to be evolutionarily hardwired.

No law of nature forbids a much longer lifespan, and life extension has been achieved in test animals. But no proven method exists for humans; this is a future expectation, not a current scientific reality.

Well supported: in comparative studies, popular diets differ little from each other as long as calorie intake decreases. Which diet you stick to determines the success. → Is a low-carbohydrate or ketogenic diet good for longevity?

This is consistent with nutrition and exercise science: no single food or form of training is sacred or forbidden. The overall pattern and sustainability determine the result.

Pharmacologically correct: melatonin is absorbed quickly and peaks roughly within an hour. This is why the common advice is to take it 30 to 60 minutes before bedtime. → How much melatonin should you take to sleep better?

Direct research on taking melatonin in the middle of the night is virtually absent. Even so, the conclusion fits with how melatonin works: it shifts your clock rather than inducing sleep, and taking it late can even push your rhythm in the wrong direction. → How much melatonin should you take to sleep better?

Short-term use at low doses (0.5 to 3 mg) has been found to be remarkably safe in research, with only mild side effects at most. Caveats: long-term data are scarce, and the actual strength of over-the-counter products often differs considerably from what the label states. → Is it safe to take melatonin every night?

This is where the evidence for melatonin is strongest: for shifting your rhythm, as in jet lag, it demonstrably works, provided it is taken at a low dose and at the right time. → Does melatonin as a supplement really work for better sleep in older age?

As a comparison of evidence bases this is correct: meta-analyses exist for melatonin, whereas cherry juice, chamomile and kiwi are supported mainly by small individual studies. One caveat: more evidence is not the same as a large effect; melatonin primarily shifts your internal clock and is not a sleeping pill. → Does melatonin as a supplement really work for better sleep in older age?

Well supported: untreated sleep apnea has been linked in large cohort studies to higher mortality, cardiovascular disease, poorer metabolism, depression and cognitive decline. Treatment such as CPAP reverses part of this. → How dangerous is sleep apnoea?

This is consistent with estimates from population research: the vast majority of moderate to severe sleep apnea goes undiagnosed, and even more so in women because their symptoms look less 'classic' (fatigue rather than loud snoring). → How dangerous is sleep apnoea?

Screening research among elite athletes does indeed find that around half sleep poorly or are at risk of a sleep disorder. But screening is not a diagnosis; 'half have a clinical sleep disorder' is a stronger claim than those studies actually support.

Sound is a proven sleep disruptor, even when it does not wake you up; nighttime traffic noise has been linked to poorer sleep quality. But research does not support the ranking of 'more than almost any other factor': light, caffeine, alcohol and sleep apnea also carry significant weight.

Measurements show more disturbances with a bed partner (movement, snoring), but in questionnaire research people who share their bed often report sleeping better and feeling safer. It depends strongly on the partner and on how you measure.

A few small studies (including ones involving athletes) found better sleep after eating two kiwis before bedtime, but without a placebo group and with only handfuls of participants. A charming signal, but not a proven sleep aid.

No trial has investigated this protocol. What exists is clinical anecdote plus a mechanistic hypothesis; as a treatment it is not substantiated. → How do I know whether I have enough vitamin D, and should I be supplementing?

Small studies show vitamin D influences the microbiome, but the chain to B-vitamin production and symptoms is the guest's hypothesis, not demonstrated in humans. → How do I know whether I have enough vitamin D, and should I be supplementing?

Correct: older skin produces considerably less vitamin D at the same sun exposure. Exactly why supplementation advice rises with age. → How do I know whether I have enough vitamin D, and should I be supplementing?

Clashes with what human studies show: weight loss with GLP-1 does cost muscle mass, which is exactly why it calls for strength training and enough protein. → Do you lose muscle mass when losing weight with a GLP-1 medication, and how do you prevent it?

The guest's personal experience; there is no published research on microdosing. Our answer on it stands at insufficient evidence. → What are the effects of microdosing with Ozempic?

Holds up at its core: a large randomised trial in over 17,000 people with cardiovascular disease found 20% fewer serious events. Caveat: shown in patients, not in healthy people. → Do GLP-1 medications (such as Ozempic) help you age more healthily?

GLP-1 helps with weight loss, and losing weight can improve the cycle. But restoring PCOS itself or fertility has not been shown; no trial has investigated this. → Do GLP-1 medications (such as Ozempic) help you age more healthily?

This is mostly lab work so far: measurements show that blending in plastic releases particles, but the number of studies is small and health effects have not been examined. An interesting signal, not yet an established fact. → How harmful are microplastics in your body to your health?

Correct: thermal paper contains free BPA and skin absorption has been demonstrated; the EU banned BPA in receipts in 2020 for that reason. Mainly relevant for people handling them daily, not for one loose receipt. → How harmful are microplastics in your body to your health?

Nanoplastics have amply been shown in bottled water, and uptake through the gut has been seen in lab models. But how much really enters the body in humans, and what it does there, is still open. This research field is moving fast; we are tracking it. → How harmful are microplastics in your body to your health?

Well supported: with heating and with acidic or fatty contents, plastics release measurably more plasticisers and bisphenols. So better not to store or reheat hot food in plastic; a simple win without hassle. → How harmful are microplastics in your body to your health?