The five things doing the most damage:

1. Bright screens in the two hours before bed
Not because of stimulating content — because of the light they emit. Specific short wavelengths suppress melatonin at the biological level, every night, invisibly. The phone on the nightstand isn't just a habit problem. It's a hormonal one. Nothing else on this list operates as consistently or as silently.

2. Irregular sleep and wake times
Your circadian rhythm is a biological clock, not a preference. Every significant lie-in, every late night, recalibrates it. The body can adjust — but until it does, melatonin and cortisol peak at the wrong hours. The weekend lie-in that feels like recovery is often the reason Monday night is hard.

3. Alcohol
The most misunderstood disruptor because it genuinely accelerates sleep onset. What it also does: suppresses REM sleep, elevates body temperature through the night, and causes the rebound wakefulness that wakes you at 3 a.m. feeling worse than before you drank. The hours are there. The architecture is gone.

4. Unprocessed stress carried to bed
Cortisol should be at its lowest point when you sleep. Unresolved stress — the email you're mentally composing, the decision you haven't made — keeps the system running. The racing mind at midnight is not a personality trait. It's an elevated cortisol state that melatonin cannot override.

5. A large meal close to bedtime
Digestion keeps the body metabolically active in ways that conflict with the temperature drop that enables deep sleep. It reduces time in slow-wave sleep — the stage where growth hormone is released. For anyone training, this is quietly borrowing from the recovery you earned.

Five things people swear by — and how much they actually deliver:

1. Melatonin supplements
The most overprescribed thing in the sleep category.

Melatonin is a timing signal, not a sedative. The doses most supplements come in — 3, 5, 10 mg — are ten to a hundred times what the body actually produces naturally. The result isn't better sleep, it's a pharmacological override that lingers into morning. That groggy, heavy feeling the day after isn't a sensitive reaction. It's your receptors still saturated with a hormone that was supposed to clear hours ago. Use the lowest dose you can find, timed correctly — or better yet, fix the light environment that's suppressing your natural production in the first place.

2. Magnesium
Genuinely useful. Not magic.

Supports GABA — the neurotransmitter responsible for calming the nervous system. For people running a deficiency, which is common in anyone training hard or under chronic stress, it produces real improvement in sleep quality and muscle relaxation. Worth doing. Won't overcome a disrupted light environment.

3. Kiwi fruit before bed
Stranger than it sounds, and actually supported.

Two kiwis consumed an hour before sleep is one of the more unexpected findings in sleep nutrition research — participants fell asleep faster, slept longer, and reported better sleep quality. The proposed mechanism involves serotonin content and antioxidant activity. It sounds like the kind of thing someone made up, but the study exists and the effect is real enough to be worth trying. Low downside. Genuinely odd that this isn't talked about more.

4. Tart cherry juice
One of the few food sources of melatonin with actual data behind it.

Montmorency cherries contain melatonin and tryptophan, and concentrated tart cherry juice has shown modest improvements in sleep duration and quality in multiple trials. Not a dramatic effect, but a real one — and unlike supplemental melatonin, the dose is physiological rather than pharmacological. The health nerd version of this involves tart cherry extract capsules. Both work roughly the same way.

5. Pomegranate juice
In the category of "plausible but not proven."

High in polyphenols and antioxidants that support melatonin synthesis and reduce oxidative stress — a real factor in sleep quality, particularly for people training hard. The evidence is thinner than tart cherry, and the mechanisms are more indirect. Still, it sits in the same corner of the market as tart cherry juice: a food intervention with a biological rationale rather than a marketing one.

6. No caffeine after noon
Directionally right. Personally variable.

Caffeine's half-life is five to seven hours. A 3 p.m. coffee still has half its alerting effect at 8 or 9 p.m. The noon cutoff is a reasonable default. But individual variation in caffeine metabolism — governed by a specific liver enzyme — is significant. Some people clear it quickly; some carry it well into the night. The noon rule is a good place to start, not a universal law.

7. A consistent bedtime
The highest-leverage habit. Consistently undersold.

When you sleep and wake at the same time every day, melatonin rises at the same time each evening and cortisol peaks at the same time each morning. The body knows what to expect and runs the sequence efficiently. More impactful than most supplements — and costs nothing. The difficulty is that modern life pushes hard against it, which is exactly why it works when you protect it.

8. Cold showers before bed
Mechanistically sound. Modestly effective.

Core temperature needs to drop for sleep onset to occur. A cold shower doesn't directly cause this — it briefly raises alertness — but the rebound cooling effect can support the transition. For some people it works as a reliable ritual signal. Real but secondary. Keeping the bedroom cool achieves the same mechanism with less commitment.