A guide · Travel & sleep
Jet lag, measured.
A 2025 study tracked sleep before and after 64,847 trips. Sleep length bounced back in about two days. Sleep timing was still shifted two weeks later.
General information for frequent travellers and flight crew. Not medical advice, and not a fatigue or fitness-to-fly assessment.
Published
After a long trip
Sleep length recovers fast. Sleep timing doesn’t.
Sleep length, all trips
Back to within about 12 minutes of usual by day 2; slightly short for longer after long eastward trips.
Deep and REM sleep, after long eastward trips
Below usual for up to about a week.
Sleep timing, all trips
Still not fully back to usual at day 15.
01 The research
Sixty-four thousand trips.
Researchers at the National University of Singapore and Oura analysed de-identified sleep data from 57,240 people wearing an Oura Ring. They followed 64,847 outbound trips of at least 1,000 km, from North America and Europe, between June and October 2023, for 15 days before and after each trip. That’s about 1.5 million nights.
02 Finding
The trip starts the night before.
Sleep was 30 to 50 minutes shorter than usual on the night before a trip across time zones, mostly because people woke earlier. Long eastward trips, which tend to leave in the evening, cost less sleep the night before, but their flight night was the shortest of all: about an hour less than usual.
03 Finding
Sleep length recovers in about two days.
The night after arrival brought a rebound. From the second day, sleep length was back within about 12 minutes of normal on average. After long eastward trips it stayed slightly short, by less than 15 minutes, for about a week.
04 Finding
Sleep timing takes far longer.
Bedtimes and wake times sat up to about an hour off their usual pattern in the first days after long trips. On average, they still hadn’t fully returned to normal 15 days later.
That’s the gap a sleep score can hide: enough hours, at a shifted time.
05 Finding
East is harder.
Disruption was worse after eastward trips and across more time zones. After long eastward trips, deep and REM sleep stayed below normal for up to about a week.
That fits CDC guidance: on average, the body clock adapts by about an hour a day after flying east, and about an hour and a half a day after flying west.
06 General principles
What helps, in general terms.
Light is the strongest time signal the body clock has. CDC guidance explains that bright light in the morning, after the body’s overnight low point, moves the clock earlier, while light in the evening moves it later. The right timing depends on the direction and the number of time zones.
Shifting sleep by an hour a day for two or three days before a trip may shorten the adjustment, according to the CDC. For healthy adults on regular schedules, the consensus recommends no more than 1 lux melanopic EDI at the eye during sleep. Visual safety and accessibility requirements take precedence. A regular daily pattern of light and dark helps keep the clock aligned.
The limit: these are general principles. A specific trip needs its own plan. Decisions about melatonin or sleep medication sit with a clinician and, for licence holders, with aeromedical advice.
Read: CDC Yellow Book 2026 · Brown et al., PLOS Biology, 2022
07 Aviation
For flight crew.
Crew live this every rotation, with constraints holiday travellers don’t face: duty limits, early reports, minimum rest and nights through the window of circadian low. This was not a study of flight crew, and the authors suggest most participants were holiday travellers with more flexible sleep schedules.
Your operator’s fatigue risk management and your AME’s advice come first. The study points to two simple habits: judge recovery by timing as well as total, and protect the night before. CDC guidance adds a third: treat light as part of the plan. Zensu for Aviation builds those into planning around the roster.
08 Caveats
The limits of the data.
- Oura Ring users; the authors presume most were on holiday, with flexible schedules.
- Outbound trips only: about 90% from North America and 10% from Europe.
- Sleep timing measured by a wearable, without a laboratory measure of the body clock.
- Not a study of flight crew; atypical baseline sleep episodes were excluded.
- One of the four authors works for Oura.
The authors describe it as the most comprehensive picture of travel-related sleep disruption to date.