SINGAPORE: Travelling across time zones affects more than just how long you sleep — it also disrupts when and how you sleep, with these effects lasting much longer than many might expect, according to a landmark study conducted by researchers at the Centre for Sleep and Cognition at the NUS Yong Loo Lin School of Medicine (NUS Medicine) in collaboration with wearable tech company ŌURA.
The study, led by Senior Research Fellow Dr Adrian Willoughby and Professor Michael Chee, Director of the Centre for Sleep and Cognition at NUS Medicine, examined more than 60,000 trips and analysed 1.5 million nights of sleep data collected via the Oura Ring, a smart ring used to monitor sleep and health metrics. It is the largest real-world study of jet lag recovery ever conducted.
While most travellers tend to regain normal sleep duration within two days after a flight, the study found that sleep timing — the ability to fall asleep and wake up in sync with the local time — can remain disrupted for more than a week. Sleep architecture, including the number of nighttime awakenings and sleep cycles, also takes significantly longer to normalise.
The research also highlighted how factors beyond time zone changes can contribute to sleep disturbance during travel. Travellers often have shortened sleep the night before a flight due to early departures, while overnight flights frequently result in poor sleep, leading to next-day fatigue and a shift towards earlier bedtimes and longer sleep the following night.
However, the recovery process becomes more complicated when jet lag interferes with the body’s circadian rhythm — the internal clock that regulates sleep-wake cycles — making it harder to fall asleep at appropriate local times even when sleep duration has returned to normal.
A key strength of the study was its extensive monitoring of participants’ habitual sleep patterns before and after travel, providing a detailed picture of how sleep is affected throughout the entire travel and recovery process.
Looking ahead, the researchers plan to explore how lifestyle factors — such as light exposure and the use of melatonin — may influence the speed of sleep recovery in real-world settings.
