Sleep hygiene basics: what the literature actually supports

"Sleep hygiene" is the umbrella term clinicians use for behavioural rules that support sleep. The list circulates widely; the evidence behind individual items varies a lot.

What the literature most consistently reports#

Consistent sleep timing. Studies of shift workers and college students show that variability in bed and wake times, even when total sleep duration is held constant, is associated with worse sleep quality and daytime alertness. A regular schedule appears more important than a "perfect" duration.

Light is the strongest external cue. Morning bright light, particularly outdoor light within an hour of waking, is the most robust environmental anchor for circadian rhythm in the human chronobiology literature. Evening bright light, conversely, delays the circadian phase.

Temperature matters more than people think. Core body temperature falls as you fall asleep; cooler bedrooms (around 16–19 °C in most studies) are associated with shorter sleep onset and more slow-wave sleep. Very hot environments fragment sleep markedly.

Caffeine has a long half-life. The mean half-life in healthy adults is around 5 hours, but it varies from roughly 2 to 10 hours depending on genetics (CYP1A2), pregnancy, oral contraceptives, and liver function. A 200 mg dose taken at noon can still leave clinically relevant levels at bedtime in slow metabolisers.

Stimulus control. The behavioural rule "if you can't sleep in 20 minutes, get out of bed" comes from cognitive behavioural therapy for insomnia (CBT-I) and is one of the few hygiene rules with high-quality RCT support. But it's specifically for insomnia, not for the general population.

What is weaker than commonly claimed#

The blanket claim that "screens before bed wreck sleep" is more nuanced than slogans suggest. The effect of evening screen light on melatonin in controlled lab conditions is real but modest, and the behavioural effects of content (anxiety, alertness, doomscrolling) may matter more than the photons.

Alcohol is often filed under "sleep hygiene" but is better understood as a sleep disruptor: it shortens sleep latency at the cost of REM sleep and second-half-of-night fragmentation.

Useful starting points#

• Wake at the same time every day, including weekends. Drift comes from variable wake times more than variable bedtimes.
• Get outside in daylight within an hour of waking.
• Keep the bedroom cool, dark, and quiet.
• Stop caffeine at least 8 hours before your target bedtime; longer if you suspect slow metabolism.
• Use the bed for sleep, not for working or scrolling.

None of this is medical advice. If you have persistent insomnia, NHS-recommended first-line treatment is CBT-I — your GP can refer you, and the NHS app Sleepio is available via prescription in some areas.