Short answer: Your body clock shifts about an hour a day. The fastest fix is light at the right time: morning daylight after flying east, evening daylight after flying west, plus sleeping on local time from day one.
Jet lag happens when your body clock is still on the time zone you left. It causes poor sleep, daytime tiredness, low concentration and an upset stomach.
Why east is harder than west
Flying west makes your day longer, and most people find it easier to stay up late than to fall asleep early. Flying east shortens your day and asks your body to sleep before it is ready. A common rule of thumb is that the body adjusts by about one hour per day, so a large time difference can take several days.
Light is the strongest signal
Daylight is what resets your body clock most powerfully.
- After flying east: get bright light in the morning and avoid bright light late in the evening.
- After flying west: get light in the late afternoon and evening to help you stay up.
Ten to thirty minutes outdoors at the right time does more than any app.
A simple plan
- Shift a little before you go. For a few days, move your bedtime an hour towards the destination's time.
- Set your watch on boarding. Sleep or stay awake on the plane according to the destination's time.
- Drink water, go easy on alcohol. Cabin air is dry, and alcohol makes sleep worse.
- Live on local time from day one. Eat meals at local times and keep any nap under 30 minutes.
Good to know: Melatonin is sometimes used for eastward jet lag, but rules on buying it differ by country and it doesn't suit everyone. Ask a doctor or pharmacist before using it.
Questions people ask
Q: Is jet lag worse on longer flights?
A: Jet lag depends on time zones crossed, not hours in the air. A long north-south flight causes tiredness but little jet lag.
Q: Should I sleep as soon as I arrive?
A: If you arrive in the morning, try to stay awake until a normal local bedtime, with at most a short nap. Sleeping for hours in the day keeps you on the old time.