Sleep Hygiene: What the Science Actually Says

Sleep hygiene has become a cottage industry of conflicting advice, much of it delivered with the authority of science but without the citations. Let's deal in specifics: what the research actually supports, ranked roughly by effect size.

Temperature: The Most Underrated Variable

Core body temperature must drop approximately 1–2°C for deep sleep to initiate. This is not optional — it's physiological. A bedroom temperature between 16–18°C (60–65°F) has the strongest evidence base of any environmental sleep variable. Most people sleep in rooms that are 2–4 degrees too warm.

Consistent Sleep and Wake Times

Your circadian rhythm is regulated by light and time cues. Going to bed and waking at consistent times — including weekends — is the single most effective intervention for sleep quality over time. The "sleep debt" you try to recover on weekends actually disrupts your rhythm further, making Monday worse.

Light Exposure: Both Ends Matter

Morning light exposure (10–30 minutes of natural light within an hour of waking, ideally outside) sets your circadian anchor for the day and makes sleep onset easier that night. This is free, accessible, and dramatically underused.

Evening light suppresses melatonin production. Blue-wavelength light from screens is the most potent suppressor, but the total amount of light matters too. Dimming all lights in the two hours before sleep is more effective than blue-light glasses alone.

What Doesn't Help as Much as You Think

• Melatonin supplements work best for shifting circadian timing (jet lag, shift work), not for general sleep quality in healthy adults. Most people take doses 10–50x higher than effective.
• White noise helps some people, but the evidence is modest and individual variation is high.
• Sleep tracking apps often cause "orthosomnia" — anxiety about sleep data that impairs sleep more than the tracked issues themselves.

The Caffeine Half-Life

Caffeine's half-life is 5–7 hours, meaning a 3pm coffee still has half its caffeine in your system at 9pm. A quarter remains at midnight. Most people significantly underestimate how long caffeine affects sleep quality, even when sleep onset feels normal. Cutting the last coffee to before noon shows measurable sleep architecture improvement for most people.

The research on sleep is clear: the basics matter far more than any supplement, device, or optimisation hack.