Modern Wisdom

Correct, and this has been well studied in humans. Regular cold exposure activates brown adipose tissue, which burns energy to generate heat, and triggers the production of new energy-generating structures within cells. What is less certain is whether this leads to noticeable weight loss or a longer life.

Correct in essence, and the evidence is stronger than for most lifestyle recommendations. Large Finnish population studies found significantly fewer cases of cardiovascular disease among people who used the sauna four to seven times a week compared to those who went once a week. One caveat: the research is observational, and people who sauna frequently tend to be healthier and more affluent in general.

There are a few small studies in which plaque thickness in the carotid artery decreased, but they are small, short-term and almost all from the same region. For a substance that acts as a blood thinner, that is far too little evidence, particularly when used alongside existing medication. A promising direction, but no proven effect.

The first part is correct: taking NMN demonstrably raises the amount of NAD in the blood, and this has been measured in multiple studies. What follows from that is far less clear. The studies on blood lipids and blood pressure are small, short-term and inconsistent in their findings. Moreover, NMN has not been approved as a food supplement in the EU.

This is exactly where resveratrol research hit a wall. In 2010, researchers showed that the measured activation was a measurement artefact: it only appeared because a fluorescent label had been attached to the test protein, and disappeared as soon as the experiment was run with the actual protein. The claim that resveratrol directly activates this enzyme is therefore not tenable.

This has been found in mice: a diet high in these amino acids shortened their lifespan, even without the animals eating more overall. The proportions involved are extreme and unattainable through a normal diet, and the question has never been studied in humans. For people looking to preserve muscle mass in later life, the evidence actually points in the opposite direction.

In laboratory animals, restricting food intake demonstrably extends life, that much is established. But the debate centres precisely on whether the eating window matters or whether it is simply the reduction in calories that counts. Recent mouse research suggests that timing does play a role, while other work shows that eating less is the main factor. Claiming this holds 'regardless of the details' is too categorical.

In mice, this has actually happened: researchers restored vision in animals with damaged optic nerves by activating three of these factors, and that was a remarkable result. But it involved a single tissue, in an animal, under controlled conditions. There is no basis yet for the general claim that ageing in tissues can be reversed, and it has not been attempted in humans.

Research shows that physical activity, particularly in the morning, supports the biological clock and reinforces the day-night rhythm. Daylight and a consistent morning routine also help synchronise your clock, making it easier to fall asleep in the evening. However, the claim that morning exercise is a 'powerful' zeitgeber goes somewhat beyond what the current evidence can substantiate: the studies are predominantly observational and demonstrate an association, but the magnitude of the effect relative to other zeitgebers such as daylight has not been precisely established.

Research shows that morning light plays an important role in synchronising the biological clock and promoting daytime alertness. The evidence for this is consistent, although large controlled experiments in humans are still lacking. However, the claim goes further by labelling morning sunlight as 'the most powerful stimulus': that specific superlative cannot be substantiated on the basis of available research, and other factors such as a consistent sleep-wake schedule and limiting evening light also play a demonstrable role in regulating the circadian rhythm.

Research shows that REM sleep integrates memories while subtly reshaping them, which is consistent with the idea that emotional charge is processed. Nevertheless, the claim goes beyond the available evidence: the function of REM sleep is described as the integration and adjustment of memories, not explicitly as the complete removal of emotional charge. Moreover, much of this research has not established causality. The general direction is correct, but 'crucial for removing emotional charge' is stated more strongly than current science can firmly support.

Research shows that evening light suppresses melatonin production, and that morning light helps synchronise the biological clock. However, the claim reverses this: in the morning, melatonin levels are already naturally low, because melatonin is a nocturnal hormone. The suppression of melatonin by morning light is therefore a much smaller effect than in the evening, and the available evidence relates primarily to evening exposure. The direction is biologically plausible, but 'directly suppresses' implies a strong and well-established morning effect that research does not specifically describe in those terms.

It is correct that bright light in the morning suppresses melatonin production and that the suprachiasmatic nucleus (the biological clock) plays a central role in this. This mechanism is described as well understood. However, the claim states that morning light stops melatonin production, whereas the suprachiasmatic nucleus already sends an inhibitory signal to the pineal gland during the day regardless, and morning light strengthens and sharpens that signal. Furthermore, the claim specifically refers to stopping production, while research shows that what actually occurs is suppression and the fine-tuning of the biological clock, not a hard on-off switch.

Research confirms that the glymphatic system is active during sleep and that deep sleep plays the most important role in removing metabolic waste products. The claim is therefore broadly correct. However, the mechanism of expanding spaces around brain blood vessels is a more specific claim that goes beyond what available research in humans has unambiguously established; the precise workings have not yet been fully proven.

Daily tadalafil at 5 milligrams is an approved treatment for urinary symptoms caused by an enlarged prostate, so the drug genuinely does something there. However, the reasoning offered here: improved prostate blood flow and cerebral vasodilation as grounds for healthy men over forty to consider it, goes well beyond the evidence. This is a prescription medication with side effects, not a general remedy for healthy men.

Observational research shows that four or more sauna sessions per week are associated with the greatest cardiovascular health benefits and a lower risk of premature death, and that association is dose-dependent. However, the claim goes beyond the evidence on two points: a specific temperature of 79°C is not identified in the research as a threshold value, nor is a minimum duration of 20 minutes per session. Furthermore, the studies are exclusively observational, meaning no causal relationship has been established, and the evidence applies largely to men.

Research suggests that daily multivitamins do appear to offer some protection for memory in older adults, with an effect equivalent to roughly three fewer years of decline. However, the claim states 'approximately 2 years', which differs from the figure that emerges from the studies. Moreover, the evidence comes from several related studies within the same research programme, and independent confirmation is still lacking, so the conclusion is not as clear-cut as the claim implies. For other aspects of cognition and brain ageing more broadly, the evidence is limited or absent.

Well supported: randomised studies and follow-up analyses show that a cold bath immediately after strength training blunts muscle growth and part of the strength gains. Anyone training to build muscle is better off scheduling cold exposure several hours after the workout or on rest days.

This figure comes almost word for word from a randomised study conducted in the heavily polluted city of Qidong, China: a drink containing sulforaphane precursors increased benzene excretion by approximately 61 percent, from the very first day. One caveat: this is a single line of research, carried out in a specific environment.

For muscle growth, this is correct: meta-analyses show that training light to near muscular failure produces comparable muscle growth to training heavy. For maximal strength, it does not hold: heavier training consistently comes out ahead. The strength part of the claim therefore goes too far.

Research shows that muscle strength remains fairly stable for up to around four weeks after stopping training, while endurance already measurably declines after ten days. The claim reverses these two: 'visible muscle loss after ten days' does not hold up well against the available evidence. Ten days is more the threshold for fitness loss than for muscle loss. The broader point, that stopping training sooner or later leads to loss, is correct.

Muscle strength does indeed play a well-supported role in healthy ageing: losing it increases the risk of falls, disability and premature death, and strength training demonstrably reduces those risks. Bone density is also considered relevant in the research, but the evidence for it is more limited and focuses mainly on slowing loss rather than building it up. The claim goes a step further by presenting muscle mass and bone density together as one of the most important indicators of both healthspan and longevity, whereas the evidence for bone density as an independent predictor of longevity is not stated that explicitly in the available studies.