Caffeine, a competitive adenosine receptor antagonist, should be avoided for at least six hours prior to sleep initiation (or 12 hours in slow metabolizers). Daily intake should remain less than 400 mg.⁸ Alcohol, despite its sedative effects via GABAergic activation, disrupts sleep architecture through rebound arousal once metabolized.¹⁵ Similarly, chronic cannabis use reduces REM and slow-wave sleep, leading to fragmented sleep and long-term tolerance effects.¹⁶ Both substances should be avoided at least three hours before sleep.

Light exposure: Exposure to high-intensity, blue-spectrum light in the evening suppresses melatonin and delays sleep onset.⁹ Minimize screen use for at least three hours before bed. If screen use is unavoidable, use blue light filters or e-ink devices such as a Kindle. Light intensity should be minimized, and light sources should emit at lower Kelvin temperatures (e.g., 1,000–2,700 degrees Kelvin) to reduce circadian disruption. Consider using light bulbs that can switch to lower Kelvin temperatures three hours before sleep.¹⁷

Sleep environment: The ideal sleep environment is dark, cool (approximately 20° C or 68° F), and quiet. Use blackout curtains or a sleep mask to block ambient light and consider earplugs or white noise machines to mitigate environmental noise. Avoid visible clocks in the bedroom, as time-checking reinforces arousal and promotes sleep-onset anxiety.¹⁸

Post-waking routine: Morning light exposure—particularly blue-spectrum light at 10,000 lux for 30 minutes upon waking either by natural sunlight, by a light emitting screen or light emitting eye glasses—promotes circadian alignment and may enhance mood.¹⁹ This practice using artificial light is especially beneficial in regions with limited sunlight during winter months or in individuals with delayed sleep phase tendencies (e.g., adolescents and young adults).

Shift Work Adaptation

Several scheduling principles and physiological countermeasures can facilitate circadian alignment and performance optimization for emergency physicians engaged in shift work.

Shift scheduling: Casino shifts (e.g., 10 p.m.–4 a.m. and 4 a.m.–10 a.m.) preserve partial overnight sleep (anchor sleep), reduce circadian misalignment, and are less circadian disruptive than night shifts that start when it is dark outside and end when it is light outside.²⁰ If casino shifts are not an option where you work, night shifts should be clustered, scheduled consecutively (two to three shifts maximum). Spacing night shifts throughout the month prolongs maladaptation and may increase performance deficits. Recovery time between shifts should be no less than 11 hours to allow adequate rest between shifts for peak performance on shift.²¹ Forward-rotating schedules (e.g., transitioning from evening to night to morning shifts) align with the natural tendency for phase delay and are preferred over backward rotations.²² Chronotype identification enables allocation of night shifts to naturally nocturnal individuals (evening types), minimizing circadian disruption and associated morbidity.²³