Your body clock is not fixed. It runs about 24.18 hours, and it listens to light, melatonin, exercise, and food. Each one shifts it in a direction that depends on when you apply it. Jet lag is what happens when the clock and the time zone disagree, and the fix is timing, not willpower.
What follows is educational, not medical advice. Ask your doctor before taking any supplement, especially with regular medication, pregnancy, or an existing health condition.
Your clock, and why it drifts
The master clock sits in the hypothalamus: a cluster of about 20,000 neurons called the suprachiasmatic nucleus, setting the timing for sleep, appetite, hormones, and body temperature. Left to itself it runs about 24.18 hours, measured in laboratory studies where volunteers lived for weeks without clocks or daylight, and daily light exposure pulls that slightly long cycle back to 24 hours.
Two hormones carry its orders. Darkness prompts the pineal gland to release melatonin, the signal that night has arrived. Morning light drives a cortisol rise that opens the day and starts the countdown to melatonin’s next evening rise, roughly fourteen hours later. Peripheral clocks in the gut and liver run their own cycles and take their cues mainly from food, which is part of why jet lag hits digestion as well as sleep: the clocks desynchronize from each other, not just from the time zone.
Because the intrinsic cycle runs longer than 24 hours, delaying is easier than advancing. Staying up later comes naturally. Falling asleep earlier fights the drift. Eastbound trips demand an advance, so they hit harder than westbound ones. CDC figures put unaided adaptation near an hour a day flying east, and around an hour and a half a day flying west. Leave a six hour eastward jump alone and it needs roughly six days to clear.
Light: the master lever
Light is the strongest signal the clock listens to, and its effect depends entirely on when it lands. Light in the hours before your body’s low point, roughly two to four hours before your habitual wake time, delays the clock. Light after that low point advances it. Same light, opposite result, separated by a few hours. That curve is the single most useful thing to understand about jet lag.
Flying east, you need an advance: seek bright light in the destination morning and avoid bright light in the late evening. Flying west, you need a delay: avoid bright early morning light and seek light in the afternoon and evening. Get outside on arrival day either way. Cloud cover still delivers far more light than any indoor room, and a morning walk outside after an eastbound flight is the most effective free move available.
Light is also a lever you can block. Sunglasses in the evening after an eastbound flight are clock management, not fashion: evening light pushes the clock later and prolongs jet lag. When daylight is unavailable, a 10,000 lux light box for 20 to 30 minutes works as a substitute.
One edge case is worth knowing. For trips crossing more than about eight time zones, the clock may adapt faster by delaying instead of advancing, since the body delays more easily. For most trips the simple east and west rules hold, but on an extreme crossing the counterintuitive direction can win.
Melatonin: a timing signal, not a sleeping pill
The most common mistake with melatonin is treating it as a sedative. It is not one. It is a timing signal: it tells the body clock where night falls. Taken at the right time it pulls the clock toward local time. Taken at the wrong time it can push the clock in the wrong direction and leave you groggy at the wrong hour.
The evidence behind it is the strongest of any jet lag remedy. Ten randomized controlled trials, pooled in a 2002 Cochrane systematic review, showed benefit in eight, with about one traveler in two gaining from treatment. The American Academy of Sleep Medicine’s 2007 practice parameters gave timed melatonin its highest recommendation level for jet lag disorder, designating it a standard treatment.
The bottle’s dose matters less than the timing. Trial results were similar from 0.5 mg to 5 mg, the CDC puts 0.5 to 1 mg as usually sufficient, and going above 5 mg adds nothing while risking melatonin still circulating at the wrong point the next day. Immediate-release beats slow-release. The practical protocol: a low dose at bedtime in the destination time zone, starting the night you arrive and continuing for the first few nights.
Two cautions. Melatonin is sold as a supplement in the US, not a regulated medicine, so tablet contents can differ from the label. And two of the ten Cochrane trials showed no benefit at all. The NHS does not endorse melatonin for jet lag, and in the UK it is prescription only, so arrange it before departure.
Exercise: a phase-response curve you can use
Exercise moves the clock too, and as with light, timing picks the direction. In a 2019 Journal of Physiology study, 99 adults did one hour of moderate treadmill exercise at set times of day for three days running. The 7 a.m. group and the 1 p.m. to 4 p.m. group shifted earlier. The 7 p.m. to 10 p.m. group shifted later. The size of the shifts matched bright light of the same duration, which makes exercise a real clock lever, not merely a way to tire yourself out.
A smaller 2016 study found the combination beat either lever alone: bright light plus exercise shifted the clock further than light or exercise by itself. That is the biohacker’s free lunch: a morning walk or run outside after an eastbound flight stacks both levers at once.
Put it to work by training in the morning at your destination after an eastbound flight, and in the evening after a westbound one. Either way, move on arrival day instead of collapsing into bed: a workout is a timing signal as much as a calorie burn.
Meals and the gut clock
Your gut runs its own clock, and food is what sets it. CDC guidance is to eat on destination time from the flight onward. Land at 6 a.m. local while your body insists it is midnight, and eat breakfast regardless: the gut clock begins to follow, and digestion is among the slowest systems to resynchronize, so an early, clear signal pays off.
The Argonne diet, a feast and fast schedule developed at Argonne National Laboratory in the 1980s, has exactly one human test behind it: a 2002 study of 186 National Guard personnel crossing nine time zones, in which followers reported less jet lag. The catch is that participants picked the diet themselves instead of being randomly assigned, and no rigorous trial has examined it since.
The simpler variant, a 12 to 16 hour fast before the first meal at destination breakfast time, is popular with frequent flyers. Its origin is 2008 mouse research from Clifford Saper’s lab at Harvard, and nobody has tested it as a jet lag intervention in humans. Interesting hypothesis, not a protocol. Meals on local time are the part the evidence actually backs. Anyone with blood sugar problems should skip fasting entirely.
Anchor sleep: the short-trip hack
A one or two day trip calls for a different strategy: do not adapt at all. CDC guidance for short trips is to hold the home schedule for sleep, meals, and activity, which avoids paying the adjustment cost twice, once on arrival and once on return.
Anchor sleep is the mechanism that makes that workable. Chronobiologists Minors and Waterhouse showed in 1981 that holding just four hours of sleep at a fixed clock time each day kept volunteers’ circadian rhythms stable, even as the rest of their sleep shifted around it. Flight crew have applied the idea on short layovers ever since: guard one unmoving block of sleep on home time and let everything else flex. On a two day business trip that translates to sleeping and eating on home time rather than wrestling the body into a zone it will leave within 48 hours. The support comes from small laboratory studies, not large travel trials, so read it as a sound strategy rather than a proven cure.
Caffeine: two effects, one cutoff
Caffeine works two ways on jet lag, and only one of them is the familiar one. The familiar effect is adenosine blockade: caffeine blocks adenosine, the chemical that builds up sleep pressure while you are awake, which is why it keeps you alert during the local day. That alertness matters, because staying awake until local bedtime builds the sleep pressure that helps you fall asleep that night.
The less familiar effect is circadian. Science Translational Medicine published a small 2015 laboratory experiment in which five volunteers took a double-espresso dose of caffeine three hours before their normal bedtime. The caffeine pushed their circadian melatonin rhythm about 40 minutes later, nearly half the effect of three hours of bright evening light. Five volunteers is a tiny sample, but the result shows caffeine reaches the clock itself, not just alertness. An evening coffee after an eastbound flight moves the clock the wrong way.
For jet lag the CDC’s caffeine guidance is 200 mg about every four hours during destination daylight, roughly two cups of brewed coffee, ending six hours before bedtime. Caffeine’s half-life is around five hours. Keep it to the local morning and early afternoon, and none in the evening.
Sleep architecture after a time-zone jump
Sleep quality is not just hours in bed. Researchers describe it with concrete measures: how long it takes to fall asleep, how often you wake during the night, the percentage of time in bed actually spent asleep, and how much of the night you spend in deep slow-wave sleep and REM sleep rather than light, fragmented sleep.
Jet lag attacks every one of those measures at once, because sleep architecture depends on the clock lining up with the sleep window. Sleep at the wrong circadian phase and you fall asleep slowly, wake often, and get less deep sleep and less REM. That is why a full eight hours in bed after a long flight can still leave you groggy: the hours were there, but the architecture was not.
Naps sharpen the trade-off. A 20 to 30 minute nap can restore alertness without wrecking your first night, but longer naps cut the sleep pressure you need at bedtime, and the CDC warns they can interfere with nighttime sleep. If you are falling asleep standing up, take a 20 minute nap, set an alarm, and get outside into daylight right after.
There is no shortcut that fixes sleep architecture while the clock is still wrong. The levers that reset the clock, light, melatonin, exercise, meals, are what restore deep sleep and REM. For the longer game of sleep quality once the clock is aligned, see our guide to how to improve sleep quality naturally.
The eastbound protocol stack
Everything above combines into a single sequence. This is the sample stack for an eastbound trip, New York to London. For the full trip protocol with westbound guidance and in-flight detail, see our guide to how to beat jet lag.
Three days before: shift sleep one hour earlier each day. Get bright light in the morning, keep lights dim in the evening, and shift meals an hour earlier with sleep. Keep your eye mask, earplugs, and melatonin in your carry-on, never in checked luggage.
Flight day: set your watch to London time when you board. Eat meals on destination time. Drink water through the flight and skip alcohol, which fragments sleep. Sleep during the middle of the overnight flight, when it is night at your destination.
Arrival day: get outside into daylight as soon as you land. Walk or run in the morning, outside, to stack light and exercise. Caffeine in the morning only. No nap, or a 20 minute nap at most. Eat dinner at a normal local time. Dim the lights an hour before bed. Take low dose melatonin at bedtime. Sleep in a dark, quiet room.
Day two and three: repeat the morning light and morning movement. Most travelers feel substantially better by day three and fully adapted within about a day per time zone crossed.
For the travel-planning side, including day-by-day westbound plans, in-flight sleep strategy, and what to do when your hotel room is not ready, see the full travel guide to beating jet lag, with day-by-day plans: Anti Jet Lag Supplements and Tips That Actually Work.
For the clinical evidence behind melatonin and light therapy, and when jet lag needs a doctor, see Jet Lag: What Melatonin and Light Therapy Actually Do.
Frequently asked questions
Can you really reset your body clock, or just cope with jet lag?
You can shift it. Light, melatonin, exercise, and meals each have a phase-response curve: applied at the right time they move the clock earlier or later. Caffeine and naps help the symptoms, but the clock levers change the underlying timing.
What time should I take melatonin for jet lag?
At bedtime in the destination time zone, starting on the night you arrive and continuing for the first few nights. Timing matters more than dose: 0.5 to 1 mg is often enough, and taking it at the wrong time of day can push your clock in the wrong direction.
Does exercise help with jet lag?
Yes, and timing decides the direction. A 2019 study found morning and afternoon exercise shifted the clock earlier, evening exercise later. Exercise in the morning after an eastbound flight, in the evening after a westbound one. Light plus exercise together shifts the clock more than either alone.
Should I fast before a long flight?
The evidence is thin. The 12 to 16 hour fast idea comes from mouse research and has never been tested as a jet lag intervention in humans. Meals on destination time are the part the evidence actually backs. Anyone with blood sugar problems should skip fasting entirely.
What is anchor sleep?
Keeping a fixed block of about four hours of sleep at the same clock time every day, even when the rest of your schedule moves. A 1981 laboratory study found it stabilized circadian rhythms. Aircrew use it on short layovers. For a one or two day trip, it is the practical version of the CDC’s advice not to adapt at all.
How fast can you adapt to a new time zone?
Unaided, about one hour per day eastbound and one and a half westbound. Timed light, melatonin, exercise, and pre-trip shifting shorten that, but a six hour eastward jump still takes several days.
Sources
- Riedy SM, Williams SG. Jet Lag Disorder. CDC Yellow Book, 2026 edition. Centers for Disease Control and Prevention, April 23, 2025. https://www.cdc.gov/yellow-book/hcp/travel-air-sea/jet-lag-disorder.html
- Herxheimer A, Petrie KJ. Melatonin for the prevention and treatment of jet lag. Cochrane Database of Systematic Reviews, 2002. https://pubmed.ncbi.nlm.nih.gov/12076414/
- Morgenthaler TI, Lee-Chiong T, Alessi C, et al. Practice Parameters for the Clinical Evaluation and Treatment of Circadian Rhythm Sleep Disorders: An American Academy of Sleep Medicine Report. Sleep, 2007; 30(11): 1445-1459.
- Czeisler CA, Duffy JF, Shanahan TL, et al. Stability, precision, and near-24-hour period of the human circadian pacemaker. Science, 1999; 284(5423): 2177-2181. https://doi.org/10.1126/science.284.5423.2177
- Burke TM, Markwald RR, McHill AW, et al. Effects of caffeine on the human circadian clock in vivo and in vitro. Science Translational Medicine, 2015; 7(305): 305ra146. https://pubmed.ncbi.nlm.nih.gov/26378246/
- Youngstedt SD, Elliott JA, Kripke DF. Human circadian phase-response curves for exercise. Journal of Physiology, 2019; 597(8): 2253-2268. https://doi.org/10.1113/JP276943
- Youngstedt SD, et al. Circadian Phase-Shifting Effects of Bright Light, Exercise, and Bright Light + Exercise. Journal of Circadian Rhythms, 2016; 14(1): 2. https://doi.org/10.5334/jcr.137
- Minors DS, Waterhouse JM. Anchor sleep as a synchronizer of rhythms on abnormal routines. International Journal of Chronobiology, 1981; 7(3): 165-188. https://pubmed.ncbi.nlm.nih.gov/7239725/
- Reynolds NC, Montgomery R. Using the Argonne diet in jet lag prevention: deployment of troops across nine time zones. Military Medicine, 2002.
- NHS. Jet lag. https://www.nhs.uk/conditions/jet-lag/
This article is for education, not medical advice. Ask your doctor before taking supplements or changing medication, and seek medical advice if sleep problems continue for weeks after a trip.