Light is the master clock signal
Your circadian rhythm is primarily regulated by light exposure. To shift your body clock forward (flying east), seek morning light on arrival and avoid evening light. To shift backward (flying west), seek afternoon and evening light and stay in the dark in the morning. Even 20 minutes of outdoor light at the right time is more powerful than any supplement.
Start adjusting your schedule before you fly
Three days before a significant eastward flight, go to bed one hour earlier each night and wake one hour earlier. For westward flights, do the opposite. This pre-adjustment reduces the adjustment needed on arrival from 6 hours to 3 hours, which is the difference between one day of grogginess and three days of it.
Use melatonin strategically, not habitually
Melatonin (0.5mg to 1mg is sufficient, not the 5mg to 10mg commonly sold) helps signal to your body that it is time to sleep. Take it at your destination's local bedtime for the first three nights. It does not make you sleep; it makes your body more receptive to sleeping at the new time. Higher doses cause more vivid dreams and grogginess without additional benefit.
Eat at local meal times from day one
Meal timing is a secondary zeitgeber (time cue) for your body clock. Eating breakfast at local breakfast time and dinner at local dinner time reinforces your light exposure signals. Avoid snacking at odd hours. A mild fast on long flights (eating only a light meal shortly before landing) has good evidence behind it for resetting your body clock on arrival.
Avoid alcohol on the flight and caffeine after 2pm local time
Alcohol on flights dehydrates you and fragments your sleep architecture, leaving you less rested than no sleep at all. Caffeine has a half-life of 5 to 6 hours, meaning a coffee at 4pm is still 50 percent active at 10pm. For the first three days in a new time zone, cut caffeine off by 1pm local time to avoid it interfering with your first solid night of sleep.
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