Jet Lag: Research on Light, Timing and Melatonin

What jet lag is

The CDC Yellow Book describes jet lag disorder as a sleep disorder caused by rapid travel across time zones, which temporarily separates the internal body clock from local time. Symptoms can include sleep disturbance, impaired thinking, daytime sleepiness, general malaise and stomach upset. [1] The same chapter says risk factors include the number of time zones crossed, exposure to appropriate time cues at the destination, individual genetic differences and medicines. [1] It adds that adjusting after westward travel averages about 1.5 hours a day and after eastward travel about 1 hour a day. [1] The NHS lists the main symptoms as trouble sleeping at bedtime, tiredness, trouble staying awake in the day, poor sleep quality, and concentration and memory problems. [2]

Light and timing

The Yellow Book lists timed light exposure, strategic scheduling of sleep, and timed melatonin among standard treatments for jet lag disorder in frequent travelers under American Academy of Sleep Medicine guidelines. [1] The NHS advises going outside during the day after arrival because natural light helps the body clock adjust, and changing sleep times to the new time zone as quickly as possible. [2] Label: established as general advice. Specific timing plans depend on direction and number of time zones, and the sources read for this page do not support a personal schedule. For the research on light timing see light timing and circadian research and morning light and the circadian rhythm.

Melatonin: two readings

• Cochrane review (2002). Of ten trials, nine found that melatonin decreased jet lag on flights crossing five or more time zones. The authors concluded it is remarkably effective and that occasional short-term use appears safe. [3] They noted that benefit was likely greater the more time zones were crossed and less for westward flights. [3]
• Risks in that review. If taken at the wrong time, melatonin is liable to cause sleepiness and delay adaptation to local time. Case reports suggest people with epilepsy, and patients taking warfarin, may come to harm. [3]
• NHS. The NHS says medicines are not usually needed for jet lag and melatonin tablets are not recommended on the NHS for jet lag because there is not enough evidence. [2] The NHS page was last reviewed 31 May 2023, with the next review listed for 31 May 2026.
• Athletes. A 2020 systematic review of 22 studies found evidence for managing jet lag in athletes was of low quality. [4]

Label: mixed. The Cochrane review is more than 20 years old, so the two sources do not necessarily reflect the same evidence. The sources read for this page do not state melatonin's regulatory status in each country, so we do not claim it here. See melatonin for sleep for the broader picture.

Sleep medicines and caffeine

The NHS says sleeping tablets may help if you are having problems sleeping, but they can be addictive and should only be used for a short time and if symptoms are severe. It also says too much caffeine or alcohol can make jet lag worse. [2] A clinician or travel clinic can advise on any medicine.

Wearables and jet lag

Proper evidence not found in the sources read for this page that a wearable's "jet lag score" or travel adjustment estimate improves outcomes. A tracker may show sleep timing, but its sleep-stage estimates are limited; see wearables vs sleep studies.

How to judge jet-lag claims

• Does a product claim to "prevent" jet lag? Treat it as a marketing claim unless a trial tested it on travelers.
• Does the source say how many time zones and which direction?
• Is the evidence from athletes, simulated travel or real flights?