What are the common misunderstandings about jet lag?
This answer is a draft. It stays unpublished until legal review and source verification are complete.
Jet lag is a shared complaint among international travellers, and the time difference between Japan and Europe or North America is 8–14 hours. The sleep guide published by Japan's Ministry of Health, Labour and Welfare (MHLW) takes the view that the body clock is moved by light and by meal times. Here we turn that idea into practical steps for a trip to or from Japan.
The numbers
| Item | Details |
|---|---|
| Body clock cycle | Slightly longer than 24 hours (on average around 24 hours 10 minutes). Reset every day by morning light |
| Speed of adjustment | About 1–1.5 hours a day. Tokyo to London (8–9 hours' difference) takes several days to a week |
| Eastward (advancing the clock) vs westward (delaying it) | Eastward is harder (the body clock is better at delaying than advancing) |
| Using light | Get strong light in the local morning and avoid light in the local evening (sunglasses, dimmer screens) |
| Meals | Eating at the local breakfast time moves the peripheral body clocks |
| Naps | Early afternoon, 30 minutes or less. Long naps slow the adjustment |
- The MHLW *Sleep Guide for Health Promotion 2023* [健康づくりのための睡眠ガイド2023] describes morning light and regular meal and waking times as the basis for adjusting the body clock.
- Melatonin is classed as a medicine in Japan (only a prescription product for children is approved) and is not sold as a supplement in Japan. If you bring melatonin bought abroad, personal-import rules apply, such as a limit of up to two months' supply (see our article on bringing medicines into Japan).
[Verify] The speed of body-clock adjustment is a general statement from sleep medicine. Check the status of melatonin in Japan against MHLW documents.
Misunderstanding 1｜Sleeping a lot on the plane prevents it
What matters is matching your sleep to the destination's time; simply sleeping longer does not move the body clock. As a guide: if you land in the morning, sleep on the plane; if you land in the evening, stay awake on the plane.
Misunderstanding 2｜Recover with a nap on arrival
A long nap, or a nap in the late afternoon or later, stops you sleeping in the local night and slows the adjustment. If you really must, early afternoon, 30 minutes or less.
Misunderstanding 3｜A drink to fall asleep makes jet lag milder
Alcohol makes the second half of your sleep shallower and adds to dehydration. Combined with dry cabin air, it increases fatigue after arrival.
Misunderstanding 4｜You cannot shift to local time before you leave
Starting 2–3 days before departure, moving bedtime and waking time one hour a day towards destination time works with the way the body clock behaves. It is generally described as most useful for eastward travel.
Misunderstanding 5｜Young people do not get jet lag
Adjustment tends to slow with age, but younger people are affected too. Do not schedule anything important on the first day of the trip — a practice shared among Japanese business travellers.
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Sources
- Ministry of Health, Labour and Welfare, *Sleep Guide for Health Promotion 2023* [健康づくりのための睡眠ガイド2023]
https://www.mhlw.go.jp/content/10904750/001181265.pdf
- Ministry of Health, Labour and Welfare, e-Health Net, "The body clock" [体内時計]
https://www.e-healthnet.mhlw.go.jp/information/heart/k-02-002.html
- Ministry of Health, Labour and Welfare, "Personal import of medicines" [医薬品の個人輸入について] (melatonin and others)
https://www.mhlw.go.jp/stf/seisakunitsuite/bunya/kenkou_iryou/iyakuhin/yakubuturanyou/index.html
⚠️ Editorial note: the source URLs above were identified by search. Our working environment cannot reach go.jp domains, so the contents have not been checked against the text. Verify every source before publication and record who checked it and when.
About this article
What we share here are ideas and everyday practices passed down among people living in Japan, together with general information drawn from public sources. They are not official recommendations, and they are not professional instruction. Practices vary between households and regions.
This is general information. Results vary from person to person and depend on your own conditions and surroundings.
Please decide for yourself, using your own judgement, whether any of this suits your situation. We cannot accept responsibility for any damage, loss or injury arising from following this article.
This article is not meant to diagnose or manage any specific medical condition. If you are worried about your health, see a doctor rather than relying on your own judgement.
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