Beyond jet lag: New study unveils extent of travel-related sleep disruption from 1.5 million nights of data

Researchers conducted a comprehensive analysis of sleep during 60,000 trips of over 100km and utilised 1.5 million nights of de-identified data from the Oura Ring to provide the first large-scale, real-world study of jet lag recovery to date. Previous studies on jet lag have either been conducted under controlled laboratory conditions or involved specific groups like athletes or military personnel, whose characteristics may not reflect those of the general traveling public.

"We've known for some time that jet lag is a challenge for travellers, but this study provides data-driven evidence of just how persistent the impacts are, particularly when it comes to adjusting sleep timing to a new time zone," said the lead researcher of the study, Adrian Willoughby, Senior Research Fellow at NUS Medicine.

Jet lag is a known cause of sleep disturbance during travel, but it is not the only factor. Travellers often wake up early to catch flights, shortening sleep the night before departure. While flights later in the day tend to have less impact on sleep the night before traveling, sleeping on overnight flights poses challenges, often leading to impaired performance and increased daytime sleepiness. This restricted sleep typically results in early bedtimes and extended recovery sleep the next night. However, crossing time zones complicates this recovery by disrupting the ability to fall asleep at the appropriate local time.

The study found that sleep duration typically returns to baseline within approximately two days, but changes in sleep timing and structure (for example, more night time awakenings) can take more than a week, with eastward travel and crossing multiple time zones amplifying the disruption.

Additional findings include:

• Sleep duration generally recovers quickly, aligning within 15 minutes of habitual sleep duration within the first few days post-travel.

• Jet lag is more severe following eastward travel, especially for shorter trips (up to three time zones). For longer journeys, the disruption from habitual sleep patterns is similar regardless of direction, with sleep occurring 60-70 minutes earlier or later than usual. In some cases, restoring normal sleep timing and structure can take more than a week.

• There were minimal differences between men and women in travel-related sleep disruption. However, older travellers experienced slightly less impact, with a 20-year-old experiencing a 15-minute greater reduction in sleep compared to a 60-year-old over the initial post-travel days.

A notable feature of this study was its measurement of habitual sleep prior to travel over an extended period as well as a long post-travel follow up. "Wearable devices like Oura Ring that track health behaviours over time, are opening new doors for health data collection on a large scale. Travellers looking at this dataset can determine how much better or worse off they are than the population average given their existing sleep habits, trip parameters, and number of days after travel. People like to know where they stand compared to others and this dataset provides a solid basis for assessing that." Professor Michael Chee, Director of the Centre for Sleep and Cognition at NUS Medicine added.

Future work will seek to assess lifestyle factors contributing to slower or faster recovery of sleep disruption and whether efforts to time light exposure and melatonin ingestion help in real world settings.