The principle
Your circadian rhythm is set primarily by light hitting specialised receptors in the retina. To move it, you control when light reaches your eyes — and, just as importantly, when it does not.
- Travelling east — you need to shift earlier: get morning light, avoid evening light.
- Travelling west — you need to shift later: get evening light, avoid early morning light.
Getting this backwards is the most common mistake and it will delay adaptation by days.
Before you fly
- Shift your sleep one to two hours toward destination time for two or three days beforehand if the trip matters.
- Set your watch to destination time on boarding.
- Choose flight timing that lets you arrive in the local evening and go to bed at a normal local hour.
The first 48 hours
- Get outdoor light at the right local time. This is the single most effective intervention. Twenty to thirty minutes outdoors beats any indoor lighting.
- Avoid light at the wrong time. Sunglasses and, if needed, an eye mask.
- Eat at local mealtimes — meal timing is a secondary clock signal.
- Do not nap long. A 20-minute nap is fine; a two-hour nap in the local afternoon will cost you the night.
- Use caffeine early in the local day only.
Melatonin
Low-dose melatonin taken at local bedtime can help, and the evidence is stronger for eastward travel. Timing matters and getting it wrong delays adaptation. Discuss dose and timing with a clinician, particularly if you take other medication. See melatonin.
Handling the first night
You will likely wake too early (eastward) or too late (westward). Do not lie in bed frustrated — use stimulus control: get up, dim light, something dull, return when sleepy. And avoid alcohol on the flight and the first evening; it fragments sleep exactly when you need it consolidated.
Getting comfortable on the plane
Most of jet lag's misery is physical: stiffness, a body that has been folded for hours, and a nervous system that arrived activated. If you can, move before boarding and after landing; on long flights, stand and walk periodically. A short movement sequence after arrival helps drop the travel tension before you try to sleep.
How long it really takes
Roughly one day per time zone crossed up to about five or six zones, then it gets harder. East is worse than west for most people. Older travellers often adapt more slowly.