Jet lag is the gap between the time your body thinks it is and the time it actually is. The body clock shifts at roughly an hour a day on its own, which is why a six-hour time change takes the better part of a week to absorb and why a two-hour one barely registers.
Most of what is sold as a jet lag remedy has little evidence behind it. Two things have a great deal.
1. Direction matters, and it is not symmetrical
Flying west is easier than flying east. Going west lengthens your day, and the human body clock naturally runs slightly longer than 24 hours, so staying up later is working with the grain. Going east shortens your day and requires you to fall asleep before your body is ready, which is much harder to force.
Practically: a trip from Europe to North America hurts less than the same number of hours from Europe to Japan. Plan the eastbound leg to have the softer first day — and if you can choose, put the demanding part of the trip at the end of an eastbound journey rather than the start.
2. Light is the lever
Light is the strongest signal your body clock takes, far stronger than meal times or sleep effort. Getting light at the right time shifts the clock in the direction you want; getting it at the wrong time shifts it the wrong way and makes things worse.
| Direction | Seek light | Avoid light |
|---|---|---|
| Eastward (e.g. Europe → Asia) | Morning at destination | Late evening |
| Westward (e.g. Europe → Americas) | Late afternoon and early evening | Early morning |
The single most effective free intervention: go outside on the first morning after an eastbound flight, ideally for half an hour, ideally early. Daylight outdoors is many times brighter than indoor lighting and the difference is what the clock responds to. A walk beats a hotel breakfast room.
The tip that makes it worse. "Sleep whenever you feel tired on the first day." A long afternoon nap on arrival day is one of the most reliable ways to prolong jet lag, because it removes the sleep pressure you need in order to fall asleep at the local bedtime. If you must nap, keep it to twenty or thirty minutes and before mid-afternoon.
What to do on the plane
- Set your watch to the destination on boarding and start thinking in that time immediately. It sounds trivial; it changes every decision you make afterwards.
- Sleep according to destination night, not to how tired you are. An overnight eastbound flight is your best chance at genuine sleep; a daytime westbound flight is a poor time to use it up.
- Water, and less alcohol than you want. Cabin air is very dry and alcohol degrades sleep quality even when it helps you fall asleep — a bad trade on the one flight where sleep quality matters.
- Do not rely on the meal service. Airline meals are served on the airline's schedule, not your destination's. Eat when it fits the destination and skip when it does not.
The first 48 hours
- Get outside in daylight at the right end of the day for your direction.
- Eat on local time, even without appetite. Meal timing is a weaker signal than light but it is a real one.
- Hold the local bedtime within an hour, even if you are tired at seven.
- Exercise lightly — a walk is enough — and preferably outdoors, which folds it into the light exposure.
- Accept some broken nights in the first few days. They are normal and they resolve. Read rather than fight it, and keep the lights low.
For short trips, do not adapt at all
If you are away for two or three nights across a large time change, adapting and re-adapting costs more than staying put. Keep as close to home time as the schedule allows, take meetings and meals at the hours that overlap, and go home unshifted. Adaptation is only worth it when you will be there long enough to enjoy the result.
The short version
- The clock shifts about an hour a day. A six-hour change is roughly a six-day adjustment.
- West is easier than east. Plan the harder days accordingly.
- Light is the only strong lever: morning light going east, evening light going west.
- Go outside on the first morning. Daylight beats any indoor lighting by an order of magnitude.
- Do not take a long afternoon nap on arrival day.
- For a two-night trip, stay on home time and do not adapt at all.