Jet lag: how to get over it faster with light timing

To get over jet lag, time your light. After flying east, get bright light from late morning and avoid it early in the morning for the first days. After flying west, get light in the late afternoon and evening. In one trial, shifting sleep 1 hour earlier a day for 3 days before an eastward flight moved the clock about 2 hours.¹²

Why jet lag happens and why east is harder

Jet lag is the gap between your body clock and the local clock. Your sleep and alertness still run on home time, so you feel sleepy at 3 pm and wide awake at 3 am.

The clock does not jump. It slides. In studies of real travelers, it delayed about 92 minutes a day after westward flights but advanced only 57 minutes a day after eastward ones.¹ Eastman and Burgess sum it up: the human clock is much harder to advance than to delay.

That asymmetry gives you a rough recovery time:

• New York to Paris (6 zones east): about 6 days without help.
• London to Los Angeles (8 zones west): about 5 days without help.

How light resets your body clock

Light is the strongest signal the clock gets, and its effect depends on timing. The pivot point is your core body temperature minimum, or CBTmin. It usually falls 3 to 4.5 hours before your habitual wake time.¹

• Light in the hours before CBTmin pushes the clock later (a delay).
• Light in the hours after CBTmin pulls the clock earlier (an advance).

In a lab study of 21 adults, a 6.7-hour bright light pulse caused delays when centered before CBTmin and advances when centered after it. The swing from biggest delay to biggest advance was about 5 hours.³

After a long flight, your CBTmin is still on home time. That is why a sunny morning walk can help one traveler and hurt another.

Jet lag calculator: when to seek and avoid light

Start from your normal wake time at home, subtract 3 hours to estimate CBTmin, then convert that to destination time. Seek light on the side that moves you the right way. Each day you adapt, the window moves 1 to 1.5 hours toward local time.

Worked example: you usually wake at 7:00 in New York. Your CBTmin is about 4:00 New York time, which is 10:00 in Paris. On day 1 in Paris, bright light before 10:00 would push you later, the wrong way. Light from 10:00 into the early afternoon pushes you earlier.

Trip	Shift the clock	Seek bright light (first days)	Avoid bright light
East, up to 7 zones (New York to Paris)	Earlier	Late morning to early afternoon local, moving 1 h earlier each day	Early morning local
East, 8 or more zones	Later, the long way round	Morning to midday local, moving later each day	Afternoon local
West, any distance (London to Los Angeles)	Later	Late afternoon and evening local	Early morning local
Layover of about 2 days	Don’t shift	Keep home hours where you can	Light that conflicts with home time

The 8-zone cut-off comes from Eastman and Burgess. Past about 7 zones east, they plan a delay instead, because the clock often drifts the long way round anyway and delaying is easier.¹ The layover row comes from one study of a 2-day layover after a 9-hour westward flight, where keeping home sleep hours reduced sleepiness and jet lag ratings compared with switching to local hours.⁴

To run these numbers for your own flight, use the jet lag planner. It applies the same CBTmin rule day by day.

“Avoid” means real avoidance. Eastman and Burgess suggest very dark sunglasses if you must go outside during the wrong window.¹ In a dark hotel room at the wrong hour, a sleep mask or blackout curtains do the same job.

How to shift your clock before you fly

You can arrive partly adapted. The method comes from trials run by Charmane Eastman and Helen Burgess.

For an eastward trip:

1. Three days before the flight, go to bed and get up 1 hour earlier than usual.
2. Get bright light for the first 3.5 hours after waking, as in the trials.
3. Repeat, moving 1 hour earlier each day.

In their trial of 28 young adults, 3 days of this moved the clock 2.1 hours with continuous bright light (over 3,000 lux), 1.5 hours with intermittent bright light, and 0.6 hours in ordinary dim room light.² Side effects on sleep and mood were small.

Going faster did not help. A second trial (n=26) compared shifting 2 hours a day with 1 hour a day. The clock moved 1.8 versus 1.5 hours on average, not a significant difference.⁵

By day 3 the 2-hour group had trouble falling asleep because sleep had outrun the clock.⁵ The authors do not recommend more than 1 hour a day, and suggest half an hour a day for night owls when schedules allow.¹

Even 1 or 2 days of pre-flight shifting helps.¹ For westward trips, the same logic runs in reverse: later bedtimes and evening light. The 2007 AASM review found no trials of it.⁴

Does a light therapy lamp help with jet lag?

A lamp moves the clock. Whether that makes you feel better on arrival is less clear.

• Westward field trial (n=20): after Zurich to New York, 3 hours of 3,000 lux on the first two evenings delayed the clock 2.59 hours versus 1.58 hours with dim red light. Sleep, performance and jet lag ratings did not improve.⁶
• Cabin crew field trial: 15 of 75 crew returned questionnaires. The estimated effect of timed bright light (sunlight, or a lamp when there was none) was 5.3 points lower on a 64-point symptom scale, which was not statistically significant.⁷
• 2020 systematic review: across 22 studies of light, sleep, exercise, nutrition and drugs, the evidence for managing jet lag in athletes was rated low quality.⁸

The American Academy of Sleep Medicine reached a similar view. In simulations, timed light before travel shifted the clock in the intended direction, but it needs high motivation and strict compliance, and the one field trial of light on arrival was equivocal.⁴

A lamp earns its place when outdoor light is missing at the time you need it: a dark winter morning, a windowless office, or an evening arrival. Outdoors on a bright day, you usually do not need one. See the light therapy lamp picks for models that list lux at a stated distance, and how to use a SAD lamp for setup.

Who should skip bright light therapy

If you have bipolar disorder, talk to your doctor before using a bright lamp. A review of 41 studies (799 patients with bipolar depression) found 0.9% switched into mania and 1.4% into hypomania after light therapy. In the 16 patients with rapid cycling, the rate was 18.8%.⁹

Check with an eye doctor first if you have retinal disease or take a drug that makes you sensitive to light.

When to take melatonin for jet lag

For melatonin, timing matters more than the exact dose.

A Cochrane review of 10 randomized placebo-controlled trials found that 9 reduced jet lag after flights crossing 5 or more time zones. The doses that worked were 0.5 to 5 mg, taken close to target bedtime at the destination (10 pm to midnight). The number needed to treat was 2.¹⁰

The details from that review:

• 0.5 mg and 5 mg worked about equally, though people fell asleep faster on 5 mg. Doses above 5 mg added nothing.
• A 2 mg slow-release form did relatively poorly, so a short, sharp peak seems to work better.
• The benefit was smaller for westward flights.
• Taken early in the day, melatonin can cause sleepiness and delay adaptation.
• Case reports suggest people with epilepsy or on warfarin may come to harm.

An American Academy of Sleep Medicine review found 12 placebo-controlled field trials and concluded that immediate-release doses of 0.5 to 5 mg appear effective.⁴

For pre-flight advancing, Eastman and Burgess use a different schedule: 0.5 mg about 4.5 hours before bedtime, moved 1 hour earlier each day.¹ The aim there is to shift the clock, not to make you sleepy.

Two cautions. The Cochrane review dates from 2002. And in the US, melatonin is sold as a dietary supplement, not an FDA-approved jet lag treatment.¹

Labels are unreliable. In 30 supplements tested by one lab, content ranged from 83% below to 478% above the label.¹¹ In 25 US gummies, it ranged from 74% to 347% of the label, and one had no detectable melatonin.¹²

What else helps with jet lag

• Caffeine: it makes sense for daytime sleepiness, though the AASM review calls the evidence very limited.⁴ Even moderate doses taken well before bedtime impair sleep.¹ Use the caffeine half-life guide to set a cut-off in local time.
• Sleeping pills: zolpidem improved self-reported sleep in a trial of 133 travelers. In another trial (n=137) it beat melatonin on symptoms but caused more side effects. The AASM review calls daytime effects unknown.⁴
• Morning light at home: once you are back, morning sunlight and a fixed wake time anchor the clock again. The steps in how to reset your circadian rhythm apply.

Footnotes

1. Eastman CI, Burgess HJ. How to travel the world without jet lag. Sleep Med Clin. 2009;4(2):241-255. doi:10.1016/j.jsmc.2009.02.006 ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸ ↩⁹ ↩¹⁰

2. Burgess HJ, Crowley SJ, Gazda CJ, Fogg LF, Eastman CI. Preflight adjustment to eastward travel: 3 days of advancing sleep with and without morning bright light. J Biol Rhythms. 2003;18(4):318-328. doi:10.1177/0748730403253585 ↩ ↩²

3. Khalsa SB, Jewett ME, Cajochen C, Czeisler CA. A phase response curve to single bright light pulses in human subjects. J Physiol. 2003;549(Pt 3):945-952. doi:10.1113/jphysiol.2003.040477 ↩

4. Sack RL, Auckley D, Auger RR, et al. Circadian rhythm sleep disorders: part I, basic principles, shift work and jet lag disorders. An American Academy of Sleep Medicine review. Sleep. 2007;30(11):1460-1483. doi:10.1093/sleep/30.11.1460 ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶

5. Eastman CI, Gazda CJ, Burgess HJ, Crowley SJ, Fogg LF. Advancing circadian rhythms before eastward flight: a strategy to prevent or reduce jet lag. Sleep. 2005;28(1):33-44. doi:10.1093/sleep/28.1.33 ↩ ↩²

6. Boulos Z, Macchi MM, Stürchler MP, et al. Light visor treatment for jet lag after westward travel across six time zones. Aviat Space Environ Med. 2002;73(10):953-963. PubMed 12398256 ↩

7. Lahti T, Terttunen J, Leppämäki S, Lönnqvist J, Partonen T. Field trial of timed bright light exposure for jet lag among airline cabin crew. Int J Circumpolar Health. 2007;66(4):365-369. doi:10.3402/ijch.v66i4.18280 ↩

8. Janse van Rensburg DCC, Jansen van Rensburg A, Fowler P, et al. How to manage travel fatigue and jet lag in athletes? A systematic review of interventions. Br J Sports Med. 2020;54(16):960-968. doi:10.1136/bjsports-2019-101635 ↩

9. Benedetti F. Rate of switch from bipolar depression into mania after morning light therapy: a historical review. Psychiatry Res. 2018;261:351-356. doi:10.1016/j.psychres.2018.01.013 ↩

10. Herxheimer A, Petrie KJ. Melatonin for the prevention and treatment of jet lag. Cochrane Database Syst Rev. 2002;(2):CD001520. doi:10.1002/14651858.CD001520 ↩

11. Erland LA, Saxena PK. Melatonin natural health products and supplements: presence of serotonin and significant variability of melatonin content. J Clin Sleep Med. 2017;13(2):275-281. doi:10.5664/jcsm.6462 ↩

12. Cohen PA, Avula B, Wang YH, Katragunta K, Khan I. Quantity of melatonin and CBD in melatonin gummies sold in the US. JAMA. 2023;329(16):1401-1402. doi:10.1001/jama.2023.2296 ↩