Making Sense of Jet Lag
Jet Lag: what it is, why it matters, and what published guidance actually asks of you.
Direction matters: travelling east compresses the day and is consistently harder to adjust to than travelling west.
Key takeaways
- Rough adjustment rate: about a day per time zone crossed
- Harder direction: eastward
- Most useful single change: Shift your schedule by an hour a day for a few days before travelling.
- Commonest mistake: Alcohol on the flight, which worsens sleep quality.
- See a doctor if any of the signs under "When to speak to a doctor" below apply to you.
The short answer
The mismatch between your body clock and local time after crossing time zones.
Where it fits
This is part of Sleep. Guidance sets out what to look for and what to do about it, which is what the rest of this page covers.
The numbers, in one place
| Measure | Figure |
|---|---|
| Rough adjustment rate | about a day per time zone crossed |
| Harder direction | eastward |
| Strongest tool | timed light exposure |
| Eastward | seek morning light at destination, avoid evening light |
| Westward | seek evening light, avoid early morning light |
What that means in practice
Put another way, here is what it asks of you:
- Shift your schedule by an hour a day for a few days before travelling
- Switch to destination time as soon as you board
- Get outside at the right end of the day for your direction of travel
- Keep meals and activity on local time from arrival
What gets people into trouble
The mistakes that come up again and again:
- Alcohol on the flight, which worsens sleep quality
- Long naps on arrival, which delay adjustment
- Staying indoors for the first days
Where to go next
- Jet Lag: Sorting the Evidence From the Noise
- Jet Lag: A Practical Checklist
- Jet Lag — the reference entry
- What the Guidance Really Says About Insomnia
- Sleep Apnoea: Sorting the Evidence From the Noise
When to speak to a doctor
Seek urgent advice for calf pain, swelling or breathlessness after a long flight, which can indicate a deep vein thrombosis or pulmonary embolism. People with diabetes on insulin should plan dose timing with their diabetes team before crossing time zones.
Where this comes from
- NHS — Jet lag
- The Sleep Charity — travel and sleep
How this page was put together
Every figure, recommendation and warning above is taken from the guidance named in Where this comes from. Nothing on this page is inferred, summarised or generalised beyond what those bodies publish: where they give a number, it is their number, and where they are silent, so are we. Pages are rebuilt whenever the underlying record changes. Sign-off by a named clinician, where it has happened, is shown at the top of the page along with the date.
Medical disclaimer
This article is general information, not medical advice. It cannot account for your own history, medication or circumstances. Always speak to a GP, pharmacist or another qualified health professional before making changes that affect your treatment, and never delay seeking medical advice because of something you have read here. In an emergency, call 999.
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