The strongest evidence supports sleep schedule consistency — going to bed and waking at the same time every day, including weekends. This anchors the circadian rhythm, which is a biological clock driven by light exposure and core body temperature cycles. Social jetlag — the mismatch between biological clock timing and social schedule — produces measurable metabolic and cognitive impairment. Even a 1-hour weekend schedule shift has measurable effects.
Light exposure is the most powerful circadian entrainer. Bright light in the morning (ideally sunlight) advances the circadian phase and promotes earlier sleep onset at night. Artificial light — particularly blue-spectrum light from screens — in the evening delays melatonin release and pushes sleep onset later. Blue-light-blocking glasses have modest but real evidence for protecting evening melatonin. Dimming screens and overhead lights 1–2 hours before bed is more impactful than glasses.
Caffeine has a half-life of approximately 5–7 hours. A 3pm coffee means meaningful caffeine is still circulating at 10pm. More importantly, caffeine works by blocking adenosine receptors — adenosine is the sleep pressure molecule that builds throughout the day. By blocking adenosine, caffeine masks fatigue without actually restoring the neurological need for sleep. The recommended caffeine cutoff for most people is noon to 2pm, not 6pm as commonly suggested.
Room temperature between 65–68°F (18–20°C) is supported by physiology: core body temperature must drop 1–2°F to initiate sleep. A warm bath or shower 1–2 hours before bed works paradoxically — the subsequent heat dissipation from the skin accelerates core temperature decline, facilitating faster sleep onset. Exercise timing has less evidence than commonly promoted — vigorous exercise close to bedtime impairs sleep in some people but not others.