What jet lag is
Your body runs on a roughly 24-hour internal clock, the circadian rhythm, that times sleep, hunger, body temperature and hormones. It is reset mainly by light. When you fly across several time zones, the local clock jumps but your body clock does not, and for several days you are sleepy at noon and wide awake at 3 a.m. That mismatch is jet lag.
How long it lasts
The body clock shifts by only about an hour or so a day. A common rule of thumb:
- Flying east: about 1 day per time zone crossed
- Flying west: about 1 day per 1.5 time zones
Flying east is harder because you must fall asleep earlier than your body wants. The natural body clock runs slightly longer than 24 hours, so delaying it (as when flying west) comes more easily.
Worked example
New York to Paris is 6 time zones east. Without preparation, full adjustment takes about 6 days. If you go to bed and get up 1 hour earlier each day for 3 days before leaving, you arrive with only 3 hours left to shift, about 3 days of adjustment. Flying back west, the 6-hour shift takes about 4 days.
How to adjust faster
Before the trip
- Shift your sleep by an hour a day toward destination time for 2 to 4 days.
- Get plenty of rest; starting a trip sleep-deprived makes jet lag worse.
On the flight
- Set your watch to destination time as soon as you board.
- Drink water, limit alcohol and caffeine, and sleep only if it is night at your destination.
At the destination
- Light is the strongest signal. After flying east, seek bright morning light and avoid late-evening light. After flying west, get light in the afternoon and evening.
- Eat meals at local times.
- Keep naps short, under 30 minutes, and before mid-afternoon.
Melatonin and other aids
Low-dose melatonin (0.5 to 5 mg) taken at the local bedtime can reduce jet lag symptoms, especially after flying east across five or more time zones. Caffeine in the morning can help alertness. Ask a doctor or pharmacist before using melatonin or sleep medicines, particularly if you take other medications.
Short trips
For a stay of two days or less, it is often easier to stay on home time as far as possible and schedule important meetings when you would normally be awake.