How to Defeat Jet Lag, Shift Work & Sleeplessness

Tmin is the lowest point of your body temperature in a 24-hour cycle, usually 90–120 minutes before your typical wake time. You can estimate it by averaging your last 3–7 wake-up times and subtracting 1.5–2 hours. Once you know it, you can decide whether to advance or delay your circadian clock using light, exercise, and temperature around this point, which is crucial for managing jet lag and shift work.

Early in your subjective day (after Tmin), bright light exposure (preferably outdoor sunlight) advances your clock, making you fall asleep and wake earlier over subsequent days. Light in the 4–6 hours before Tmin delays your clock, making you go to bed and wake later. In the middle of the day (the circadian ‘dead zone’), light has little effect on clock timing. Evening sunset light reduces retinal sensitivity, giving you more buffer against night-time artificial light.

Traveling east (needing to sleep earlier) is harder and more detrimental than traveling west. Begin shifting your schedule 1–3 days before departure by exposing yourself to bright light and possibly exercise in the 4–6 hours after your home Tmin (to advance) or before it (to delay), depending on destination. On arrival, keep track of what your internal time still is (e.g., by remembering home clock time) and continue targeting light, activity, and meals relative to where your Tmin currently lies, rather than blindly following local sunrise advice.

If you’re traveling for only a day or two, it’s usually better to stay on your home circadian schedule rather than try to adapt to the local time zone. Use eye masks, blackout curtains, and portable light sources (e.g., a bright light pad) to simulate your home light-dark pattern. This minimizes circadian disruption so you can return home without a prolonged re-adjustment period.

If possible, stay on the same shift for at least 14 days, including weekends, to avoid constantly re-shifting your clock. During the part of the 24-hour cycle when you intend to be awake, maximize safe bright light exposure; during your intended sleep phase (often after a night shift), minimize light, screens, and overhead illumination. Again, use your own temperature pattern (rising vs. falling) instead of clock time to decide when to seek or avoid light.