Sleep Hygiene: What Works and What Is a Myth

✓Moderate evidence

Sleep hygiene is a list of a dozen rules. Some have solid trials behind them, others get copied from guide to guide because they sound sensible. Worth separating, because following these rules is not free: each one costs attention you could have spent on the one that works.

Which sleep hygiene rules actually have evidence?

A fixed wake time

If you have to choose, regularity beats duration. In the MESA cohort, objectively measured sleep regularity was linked to lower mortality regardless of how many hours people slept. Moving your wake time two hours at the weekend is, for your body, the equivalent of flying across two time zones.

Set your tolerance at about twenty minutes. Not zero, because zero is unrealistic and you will abandon the whole idea inside a fortnight.

A bedroom at 17 to 19 °C

Falling asleep requires core body temperature to drop by roughly 1 °C. Your body does this by dilating vessels in the hands and feet, dumping heat outward. In a room at 24 °C that mechanism has nowhere to go.

Okamoto-Mizuno’s review shows high ambient temperature shortens slow-wave sleep and increases awakenings, with humidity amplifying both. Warm feet in a cool room is not a contradiction, it is exactly this mechanism: socks speed up heat loss from the core.

Caffeine cut 8 to 10 hours before bed

Caffeine’s half-life is around 5 to 6 hours. Two hundred milligrams, roughly a large coffee, taken at 3 pm leaves about 100 mg circulating at 9 pm.

In Drake’s 2013 randomised trial, 400 mg taken 6 hours before bed cut total sleep time by more than an hour. The more important detail: participants did not notice. Their subjective sleep quality ratings did not differ from placebo even though the polysomnography clearly did.

If you carry the slow CYP1A2 variant you clear caffeine up to twice as slowly. You do not need a genetic test for this. If coffee after 2 pm reliably ruins your night, you have your answer.

No alcohol in the evening

Alcohol shortens sleep onset and ruins everything after it. In the first half of the night it suppresses REM, and in the second half, once it converts to acetaldehyde, it fragments sleep and causes awakenings. It also raises resting heart rate, which shows up on any tracker the next morning.

This is one of the few cases where consumer device data is unambiguous and matches the literature. Two glasses of wine at 9 pm will be visible in your morning HRV.

Which sleep hygiene rules are overrated?

Blue-light blockers do something, just less than the price suggests. A phone held in your hand delivers 30 to 50 lux at the eye, while a living-room ceiling light delivers 200 to 300. If you are going to do one thing about evening light, buy a dimmer or simply switch off the overhead light instead of buying glasses.

“Do not look at the clock at night” is sensible advice for anxiety-driven insomnia, where checking the time feeds arousal. Outside that group there is no large population effect here.

Rituals without specifics are not instructions. “Wind down before bed” says nothing. This is an instruction: overhead light off at 9 pm, phone outside the bedroom, thermostat at 18 °C.

A separate category is gadgets that measure sleep stages and are sold as diagnostic tools. Trackers are decent at telling whether you are asleep and clearly weaker at classifying stages. Making decisions because an app reported “not enough deep sleep” is making decisions on noise.

Does chronotype change the order you implement these?

The same four rules apply to everyone, but their weight depends on chronotype. For a morning type, morning light is a formality, because they are already up early and out of the house. For an evening type it is the single most important element, because without it the rhythm keeps drifting later.

Caffeine works the other way round. Evening types often drink coffee late to get through the afternoon, and cutting it gives them the biggest change. Morning types usually finish their coffee before noon anyway.

Practical read: if you are an owl and you can only add two things, add morning light and a caffeine cutoff. If you are a lark, start with temperature and weekend regularity.

How much of this will work for you?

Here comes the caveat I dislike, because it spoils a tidy conclusion. Between-person variation in response to these interventions is large. Temperature works for nearly everyone, caffeine timing for most, morning light depends heavily on chronotype, and a fixed wake time is hardest to adopt for exactly the people who would gain most from it.

I have no good way to predict which will work for you. So instead of a ranking, here is a test sequence: one change per week, two numbers logged, decision after two weeks.

Compared: cost, evidence and time to effect

Which sleep gear earns its place?

A £15 room thermometer tells you more about your sleep than a £300 tracker, because it acts on a variable you actually control.

Blackout curtains earn their place if you live under a streetlight or sleep after night shifts. The test is simple: five minutes after lights out, can you make out the outlines of furniture?

White noise machines can help against street noise, but they treat the symptom rather than the cause. Earplugs cost a fraction and work comparably.

Sleep trackers are worth treating as a tool for spotting trends and correlations with alcohol or late meals. As a source of verdicts about “not enough deep sleep”, they are not accurate enough.

When is sleep hygiene not enough?

Sleep hygiene is a first-line intervention for mild difficulty falling asleep, and it is not a treatment for chronic insomnia. For insomnia lasting over three months and occurring at least three nights a week, the first-line treatment with the strongest evidence is cognitive behavioural therapy for insomnia.

That distinction matters practically, because sleep hygiene guides get read by people who need something entirely different, and reinforce their belief that they are simply “not trying hard enough”. The clinical context and warning signs are covered in sleep and longevity.

Three questions before changing anything

Is your problem falling asleep, waking in the night, or waking too early? Those three have different causes and different fixes. Sleep onset responds to temperature and caffeine, night awakenings more often to alcohol and apnoea, and early waking is sometimes a symptom of a mood disorder.

How much do you actually sleep versus how long do you lie there? Eight hours in bed with a 30-minute latency and three awakenings is about six and a half hours of sleep. That changes the diagnosis: your problem is continuity, not duration.

Is the problem daily, or does it depend on the day of the week? If you sleep badly on Sunday and Monday and well on Thursday, this is not a hygiene problem, it is your rhythm drifting over the weekend.

In what order should you implement these?

Do not change everything at once, or you will not know what worked. One change per week, logging two numbers: minutes to fall asleep and number of awakenings.

The ready-made fourteen-day sequence is in the sleep protocol. The wider context, including mortality and insulin sensitivity data, is in sleep and longevity. If the basics are already in place and you are considering a supplement, start with glycine, which has the best-described mechanism and the lowest cost of entry.