# What actually fixes jet lag (and what only feels like it)

Nine hours west to Los Angeles, six hours east back to Munich, and one long nap that cost me three days. What the circadian research says about light timing, melatonin and how fast a body clock really moves.

Jet lag is a timing problem, not a tiredness problem. Your body clock is still running on the time zone you left. It keeps asking for sleep, digestion and hormones at the old hour, while your new location is somewhere else entirely in the day.

Sleeping in does not move that clock. Light moves it, but only at the right hour. Which hour that is depends on whether you flew east or west. That is what this piece is about.

I flew to the United States for the first time this summer. Munich to Los Angeles in one jump, then home in stages over Austin, Houston, Boston and New York.

Los Angeles runs nine hours behind Munich. New York runs six hours behind. So the way out made my day nine hours longer, and the way home made it six hours shorter.

In Los Angeles I was awake at four every morning. Four in the morning there is one in the afternoon in Munich, so my body was standing in the middle of its day while the city slept. I sat in front of a closed coffee shop and waited for it to open at six.

The way home was harder anyway, even though the shift was smaller. That was the three days after landing, when I broke nearly every rule below.

What follows is the mechanism, the numbers on how fast people really adapt, the protocols the biohackers publish, and a piece of arithmetic you can run before your next flight.

If you would rather skip the arithmetic, the jet lag planner runs it for you: two time zones and a departure time in, light, dark, caffeine and melatonin windows out as clock times. The rest of this piece explains why those hours land where they do.

What is jet lag, exactly?

Jet lag is the gap between your internal clock and the clock on the wall. The master clock sits in the hypothalamus, in two small nuclei above the crossing of the optic nerves, and it takes its main cue from light hitting your retina. Fly six zones east and that clock keeps running on the old schedule for days, which is why you lie awake at midnight and hit a wall in the late morning.

Left alone in dim light with no clocks, no daylight and no schedule, the human clock does not run at exactly 24 hours. A Harvard forced desynchrony study measured an average period of 24 hours and 11 minutes (Czeisler et al., 1999). A later study of 157 people found women averaging 24.09 hours against 24.19 for men, with 35% of the women running shorter than 24 hours (Duffy et al., 2011). Those 11 minutes are part of the reason flying west is easier than flying east, though not the whole of it. The next section does that arithmetic.

Your organs have clocks too. Liver, gut and muscle keep their own time and re-set at their own pace, which is why appetite and digestion stay strange for a few days after the sleepiness has settled down.

One thing gets blamed on jet lag but is a different problem: travel fatigue. That is the exhaustion the trip itself causes, not the time shift. Dry cabin air, hours of sitting, a short night before an early departure and the thin air of a pressurised cabin add up to dried out airways, stiff legs, a heavy head and a short temper. It hits you on a flight from Munich to Malaga too, where there is no time shift at all (Waterhouse et al., 2007).

In a study with 502 volunteers who spent 20 hours in a low pressure chamber, oxygen saturation fell by 4.4 percentage points at a cabin altitude of 8,000 feet (Muhm et al., 2007). Travel fatigue is gone after one good night. Jet lag stays until the clock has moved.

Why is flying east harder than flying west?

Because a clock that naturally runs a little long finds it easier to stretch a day than to cut one short. Flying west stretches your day, which is the direction your body drifts anyway. Flying east asks it to do the opposite.

The classic averages come from Aschoff and colleagues and are usually passed on as early estimates from real air travellers: about 92 minutes per day after a westward shift, about 57 minutes per day after an eastward one (Aschoff et al., 1975, as summarised in Eastman & Burgess, 2009). The rule of thumb the CDC still prints is the same idea rounded off, roughly 1.5 hours per day westward and 1 hour per day eastward.

[Image: Timeline of a trip from Munich to Los Angeles, Austin, Houston, Boston, New York and back to Munich, with the time shift of each leg]

My route did the hard direction in instalments without me planning it. Two hours east from Los Angeles to Austin, none on to Houston, one more to Boston, none again to New York, then six at once on the flight home. Each of the small steps was inside what the body can absorb in a day.

The one rule: light before or after your temperature low

Light does not simply wake you up. Depending on when it hits, it pushes your clock later or pulls it earlier, and the switch between the two sits at the nightly low point of your core body temperature.

That low point lands roughly three to four and a half hours before your habitual wake time if you sleep about eight hours (Eastman & Burgess, 2009), and closer to two hours before it if you sleep seven or less (Kolla & Auger, 2011). If you sleep from 23:00 to 07:00, it sits at about 04:00. This piece works with three hours as the middle case. Light in the hours after it pulls your clock earlier. Light in the hours before it pushes your clock later. Get the side wrong and you spend the morning walking your clock away from local time.

[Image: Timeline showing the body temperature low with a delay zone before it and an advance zone after it]

The effect is large enough to plan a trip around. In a laboratory phase response curve with 21 participants, a single 6.7 hour block of about 10,000 lux moved the clock by up to 3.6 hours depending on when it was given, and the curve from its largest advance to its largest delay spans about five hours (Khalsa et al., 2003). Even one hour of bright light produced delays of up to two hours in a later study, with advances reaching about one hour (St Hilaire et al., 2012). A morning walk outside is not a soft measure, it is the strongest lever you have.

The catch is that the pivot travels with you. On your first morning abroad it still sits at home time, so you have to convert it.

My temperature low at home is around 04:00 Munich time. Los Angeles runs nine hours behind, so on my first days there the pivot sat at 19:00 the evening before. Flying west means I had to delay my clock, and that calls for light in the hours before the pivot: late afternoon and early evening.

The dawn I sat in while waiting for that coffee shop was on the wrong side of the pivot. It did nothing useful, and by day three it was working against me.

With that rule in hand, one odd case stops looking like a maths error. Above roughly eight zones eastward the shift can tip in the wrong direction. Take a winter flight from Munich to Tokyo, eight hours east.

Your temperature low sits near four in the morning at home. In Tokyo that is midday. Step outside at eight in the morning there and the light reaches you four hours before your low. Light before the low pushes the clock later. So it does not move forward, it drifts backwards.

Backwards arrives at the same place, on the long way round: 16 hours back instead of eight hours forward. Clocks drift backwards at about 1.5 hours per day, so that is some eleven days. The direct route forward would be eight. Circadian researchers call the detour antidromic re-entrainment (Eastman & Burgess, 2009).

From about ten zones the arithmetic flips. The long way round is then the faster one, so you plan it on purpose: light in the evening, sunglasses in the morning, bedtime later every day. Eastman and Burgess advise planning the backwards route from about eight zones east, for a practical reason rather than an arithmetic one: the morning light waiting for you at the destination lands in the delay zone anyway. Going forward from eight zones only works if you keep the sunglasses on until your pivot has passed.

How long does jet lag actually last?

Take the number of time zones and divide: about one per day eastward, about 1.5 per day westward. Nine hours west is therefore roughly six days, six hours east is roughly six days as well. That matches how my trip felt to an uncomfortable degree.

You can buy some of those days before you fly. In a Chicago study, 28 people moved their sleep one hour earlier per day for three days. With dim indoor light in the morning their clock advanced 0.6 hours in total. With intermittent bright light it advanced 1.5 hours, with continuous bright light 2.1 hours (Burgess et al., 2003). Those last two were not significantly different from each other, so the on-off schedule is the one to copy: half an hour of light, half an hour off.

Adding melatonin in the afternoon pushed the same protocol close to a full hour per day. In a trial with 44 adults, three days of advancing sleep plus morning light produced 1.7 hours with placebo, 2.5 hours with 0.5 mg of melatonin and 2.6 hours with 3 mg (Revell et al., 2006). Two things are worth taking from that: the small dose did the same work as the large one, and nobody in the study felt jet lagged while doing it.

One hour a day is also the ceiling. Trying to advance your bedtime by two or three hours at once mostly produces a night of staring at the ceiling.

What jet lag does besides making you tired

Five findings from the literature, sorted from the hardest evidence to the softest.

1. Laboratory: metabolism slips in ten days

The sharpest human data does not come from flights at all. Ten adults lived on 28 hour days in a laboratory for ten days, which forces the clock and the sleep schedule out of alignment while diet and activity stay controlled (Scheer et al., 2009). The results at maximum misalignment:

Measure | Change under circadian misalignment
Leptin (the satiety hormone) | 17% lower
Blood glucose | 6% higher
Insulin | 22% higher
Mean arterial pressure | 3 mmHg higher
Sleep efficiency | 67% instead of 84%

Three of the eight participants with usable data showed post-meal glucose values in the prediabetic range. These were healthy people in their mid twenties, after ten days.

2. Sleep loss: performance drops, the feeling does not

Add the sleep loss that travel brings with it. In a 14 day study, 35 adults were held at eight, six or four hours in bed. Six hours produced lapses in alertness and working memory comparable to one night of total sleep deprivation, four hours reached the level of two nights, and the participants rated themselves as only slightly sleepy while their performance kept falling (Van Dongen et al., 2003). Six nights of four hours in bed were enough to lower glucose tolerance and raise evening cortisol in eleven young men (Spiegel et al., 1999).

3. Field data: 46,535 baseball games

One field data set is hard to argue with. Researchers went through 46,535 Major League Baseball games from 1992 to 2011. Home teams normally win 53.9% of their games, an edge of 3.9 percentage points. After a trip east, home teams lost 3.5 points of that edge, and both teams gave up more home runs (Song et al., 2017). Westward travel showed a smaller effect that missed significance. The study only observes, it does not prove, so take it as a strong hint.

4. Chronic exposure: thin data, loud headlines

For chronic exposure the evidence gets thinner while the headlines get louder. Twenty female cabin crew were compared after five years on the job. The group with less than five days between long haul flights had higher cortisol, a smaller right temporal lobe and worse spatial memory (Cho, 2001). Ten women per group, measured once. That is a hypothesis, not a verdict.

In aged mice, eight weeks of weekly six hour shifts cut survival from 83% to 68% when the shifts ran backwards and to 47% when they ran forwards (Davidson et al., 2006). The same asymmetry as in people, with forwards the harder direction. Young mice were fine.

5. One clarification: night shifts are not flights

One clarification, because the two get mixed up constantly. The IARC classified night shift work as probably carcinogenic in 2019 (IARC Monographs Vol. 124 Group, 2019). That assessment is about years of night work, not about your flight to New York. Air travel itself carries no such classification. The cosmic radiation at cruising altitude falls under the Group 1 entry for ionizing radiation, which is a question for crews rather than for one holiday flight.

What I got wrong on the way home

I landed in Munich at nine in the morning with a body that thought it was three at night. Then I did almost every part of it wrong.

I lay down at one in the afternoon and slept until half past four, which felt sensible and was the single worst decision of the week. I went to bed at eleven that night, slept badly, and was wide awake at three in the morning. Same again the next day. On the third night I gave up, stayed awake until three, and then slept eleven hours straight, which is a personal record and did nothing for my clock.

[Image: Four day sleep log after landing in Munich, with two long midday naps, two short nights and an eleven hour catch-up night]

Here is what each mistake did. The long midday sleep burned the sleep pressure I would have needed at eleven that night. The short night was locked in before it started.

Waking at three in the morning was simply my New York clock reporting for duty. Three in Munich is nine in the evening in New York, so that was my body at its most awake, not a sign that anything was broken.

The eleven hour night felt like recovery. But sleeping until two in the afternoon kept me away from every hour of morning light that could have pulled the clock forward.

My temperature low sat at around 10:00 Munich time on day one. The useful plan would have been sunglasses on the way home from the airport, bright daylight from ten until two, a nap of half an hour at most, and no attempt to force sleep at eleven.

A short first night with a fixed local wake time beats a long night at the wrong hour.

Is there a formula for this?

Close to one. The parts that can be calculated are the direction, the number of days, the position of your temperature low each morning and the hours in which light helps or hurts.

1. Shift: destination offset minus home offset. Positive means east, negative means west.
2. Skip rule: two zones or fewer, or a trip of two days or less, and the best plan is to stay on home time and schedule around it.
3. Direction: east means advancing your clock, west means delaying it. From about ten zones east onward, deliberately delaying is the faster route.
4. Your pivot: temperature low equals your usual wake time minus three hours, in home time. Convert it to local time by adding the shift.
5. Light windows: to advance, seek light in the four hours after the pivot and stay dark in the three hours before it. To delay, do the mirror image.
6. Daily update: move the pivot one hour earlier per day when advancing, 1.5 hours later per day when delaying, then recalculate the windows.
7. Days needed: zones divided by 1 going east, divided by 1.5 going west. Three days of pre-shifting removes about two of them.
8. Add-ons: melatonin 0.5 mg about five and a half hours before your habitual bedtime at home when advancing, caffeine cut-off eight hours before target bedtime, naps capped at 30 minutes and never inside those eight hours.

Worked through for my flight home. Munich is six hours ahead of New York, so the shift is plus six. My usual wake time is seven, which puts the pivot at 04:00 New York time, and that is 10:00 in Munich.

Day one therefore wants sunglasses until ten and bright light from ten to two. From there the pivot moves one hour earlier every day: nine, eight, seven, and after six days it is back at four. Six hours at one hour per day is six days, and that is what it took.

If that sounds like too much arithmetic, that is exactly what the jet lag planner is for. Two time zones and a departure time go in, and the light, dark, caffeine and melatonin windows come out as clock times per day. The full calculation sits underneath, so you can check every number.

[Image: Screenshot of the jet lag planner showing the day plan for a flight from New York to Munich]

Two other apps used to do this arithmetic for you, and only one of them is left. Entrain from the University of Michigan was the free one, built on published mathematics of light scheduling (Serkh & Forger, 2014), but it has vanished from both app stores and its project page no longer resolves. Timeshifter is the commercial one: the first plan is free, after that it costs 9.99 dollars per plan or 24.99 dollars a year. Its widely quoted 96.4% comes from 129,852 of its own post-flight surveys and counts users who did not report severe or very severe jet lag, so read it as self-reported and self-selected rather than a peer reviewed result.

What do the biohackers actually do?

Kate Tolo, co-founder and chief marketing officer of Blueprint and Bryan Johnson's partner, published a jet lag protocol in February 2026 after a trip to China (Tolo, 2026). Fast before and during the flight, blue light blocking glasses instead of screens, sleep straight after takeoff, earplugs and a blackout mask, plenty of water, no alcohol. On landing in the morning: sunlight, exercise, food, caffeine limited to the morning, and extended release melatonin for at least the first three nights.

[Image: Screenshot of the Blueprint article How to Beat Jet Lag by Kate Tolo]

Most of that is solid and matches the literature. What the piece does not say is what to do when you land in the evening, what dose of melatonin to take, and how the plan changes between an eastward and a westward flight. The same advice cannot be right for both directions, because the light windows are mirror images of each other.

Bryan Johnson himself published a narrower experiment in June 2026: 300 mg of slow release caffeine in the morning plus 3 mg of melatonin before bed, explicitly for eastbound recovery, with the line "The study showed a 44% faster recovery" (Johnson, 2026).

[Image: Screenshot of Bryan Johnson's post about a caffeine and melatonin protocol for jet lag recovery]

The study behind it is almost certainly a 2001 trial with 27 US Air Force reservists after a seven hour eastward flight. It tested caffeine, melatonin and placebo as three separate arms that were never combined, and the abstract contains no percentage at all (Pierard et al., 2001).

The same experiment, reported again three years later for sleep and sleepiness, found a trade-off: slow release caffeine made travellers less sleepy during the day and made their nights worse, melatonin did the opposite (Beaumont et al., 2004). Two papers, one trial, nine people per arm, and the dose was 5 mg of melatonin rather than the 3 mg Johnson takes. Johnson himself asks whether 300 mg is too much and whether 0.3 to 0.5 mg of melatonin would be enough. That is the right question. The 44% is his framing, not a published result.

Andrew Huberman's jet lag newsletter is the most practical of the three (Huberman, 2024). Start two days early, moving your wake time 30 to 45 minutes per day, use the temperature minimum to decide when to seek light, and keep using your home temperature minimum for the first two to three days after arrival. For trips shorter than three days he says stay on home time.

[Image: Screenshot of the Huberman Lab newsletter section about timing light exposure by the temperature minimum]

One detail is worth pinning down, because the estimates differ. The newsletter puts the temperature minimum about two hours before your usual wake time. Eastman and Burgess give three to four and a half hours, but for an eight hour night. The clinical rule of thumb sorts it by how long you sleep: about two hours before waking at seven hours or less, about three above that. Take the number that fits your own night.

Matthew Walker's version, from his MasterClass, is the low effort one: set every clock to destination time when you board, sleep in the first half of a long flight if it leaves around midday, then stay awake until local bedtime, 20 to 30 minutes outdoors in the morning without sunglasses, eat on local times, nap only early in the day for 10 to 20 minutes, and leave alcohol and caffeine alone while you adjust.

Melatonin: how much, and when?

Melatonin works as a clock signal here, not as a sedative. It is the only thing on the shelf that moves the pivot itself. A Cochrane review covered ten randomised trials: eight of them found less jet lag when melatonin was taken close to the destination bedtime after crossing five or more zones, and the number needed to treat was two, calculated from the only two trials that reported what it needs (Herxheimer & Petrie, 2002). The last literature search for that review ran in 2008.

Dose matters less than most people assume. Doses between 0.5 and 5 mg worked about equally well for the jet lag rating, 5 mg helped people fall asleep faster, and above 5 mg nothing improved further. Shelves still carry 10 mg capsules. No trial supports that amount, so the big number on the box is marketing. Timing matters much more, because melatonin taken at the wrong hour shifts your clock in the wrong direction. The American Academy of Sleep Medicine rates timed melatonin for jet lag as a Standard recommendation, its highest tier (Morgenthaler et al., 2007).

For a practical schedule after an eastward flight: 0.5 mg about five and a half hours before your habitual bedtime, or 3 mg about six and a half hours before it, both timed to land in the phase advancing window (Roach & Sargent, 2019). The anchor is the bedtime you keep at home, not the one waiting at your destination, and the further east you flew the further apart those two sit. The same authors prefer 3 mg, because the larger dose shifts the clock more reliably rather than further. Human phase response curves put the peak advance two to four hours before your own melatonin release starts for 0.5 mg and earlier for 3 mg, with both doses moving you about equally far when each is taken at its own best hour (Burgess et al., 2010).

British NHS guidance names 3 mg at your destination bedtime, rising to 6 mg if you need it, never before 20:00 and never after 04:00, for up to five nights and no more than 16 courses a year. That ceiling sits above what the trials could show a benefit for. Anyone with epilepsy or on blood thinners should ask a doctor first, and nobody should drive after taking it.

What if you do not want to take melatonin?

Melatonin is the only one that moves the pivot. Everything else in the usual sleep stacks aims at the second half of the problem: falling asleep at the hour your plan asks for. That is useful, and it does not replace the light windows.

L-theanine has the most usable data of the group. In a randomised cross-over trial, 30 healthy adults took 200 mg per day for four weeks. Sleep latency, sleep disturbance, use of sleep medication and the total score on the Pittsburgh sleep index came out better than on placebo (Hidese et al., 2019). The trial was paid for by the L-theanine manufacturer, with two of its employees among the authors.

Saffron extract comes next. 120 adults with unsatisfactory sleep took 14 mg, 28 mg or placebo an hour before bed for 28 days. Sleep quality and morning mood improved, evening melatonin rose and cortisol stayed where it was (Lopresti et al., 2021). 14 mg worked as well as 28 mg.

Lemon verbena is the third with real numbers. 71 people with disturbed sleep took an extract of Aloysia citrodora for 90 days. Actigraphy showed shorter sleep latency, better sleep efficiency and less time awake after falling asleep (Perez-Pinero et al., 2024). The manufacturer of the extract funded that trial too, with three of its staff among the authors. One trial, one branded extract, so a start rather than proof.

Magnesium is marketed far beyond what the data carry. A meta-analysis of three randomised trials in older adults found people falling asleep about 17 minutes faster, which was statistically solid, and a gain in total sleep time that was not (Mah & Pitre, 2021). The authors grade that evidence low to very low and call the literature substandard, while noting that cheap oral magnesium may still be worth trying for insomnia symptoms. Bisglycinate is the gentler form on the stomach, and that is all the literature says about the form.

Zinc reads better than its reputation. A systematic review of eight randomised trials found most of the adult evidence pointing to better sleep quality, on data the authors themselves call limited and not fully consistent, with no significant effect on sleep disorders and no clear answer on sleep duration (Jazinaki et al., 2024).

For taurine and glutathione there is almost no controlled human sleep data. Taurine is argued from its action on the GABA system, which is a mechanism and not yet a result. Glutathione does not appear in sleep research at all. Glycine is a different amino acid with its own sleep laboratory data, so do not carry the taurine verdict over to it.

None of these three trials looked at travellers or time zones. They are general sleep quality studies, borrowed for a jet lag context. The summary: none of these moves your body clock. If you would rather avoid melatonin, you lose the timing signal and keep a sleep aid. Light, a fixed wake time and a caffeine cut-off then carry the adaptation on their own, and they can.

Caffeine, alcohol, food and exercise

Caffeine is a clock signal too, which is easy to forget. A double espresso three hours before bedtime delayed the human circadian clock by about 40 minutes, roughly half the delay produced by three hours of bright light in the same experiment, though only five people completed that protocol (Burke et al., 2015). And 400 mg taken six hours before bed still cost more than an hour of measured sleep, while the participants’ own diaries put the loss at 41 minutes and could not tell it apart from chance (Drake et al., 2013). Coffee belongs in your destination morning, with a cut-off around eight hours before the bedtime you are aiming for.

Alcohol on a plane is worse than alcohol on the ground. In a chamber study at a cabin altitude of 2,438 metres, a blood alcohol level of 0.043% during a four hour sleep window pushed median oxygen saturation down to 85% and median heart rate up to 88 beats per minute, with participants spending most of that sleep below the clinical threshold (Trammer et al., 2024). That was about 37 grams of alcohol, more than most definitions of moderate, and the ground and altitude groups were different people rather than the same ones twice.

Exercise moves the clock in its own right. With 99 participants, one hour of moderate treadmill work produced clear delays when done between seven and ten in the evening and clear advances at seven in the morning and between one and four in the afternoon (Youngstedt et al., 2019). No significant differences by age or sex turned up, on groups too small to rule small ones out. The afternoon advance window is the useful surprise, because it is easy to hit on your first day abroad.

Meal timing does something narrower than the diet books suggest. Delaying all meals by five hours shifted the rhythm of blood glucose by 5.69 hours while leaving melatonin and cortisol where they were (Wehrens et al., 2017). Even the clock genes in fat tissue moved, by about an hour. Eating on local time re-times your metabolism, not your master clock, so it is worth doing but it will not carry the plan.

Do children get jet lag too?

Babies under about two to three months mostly do not, because they have no consolidated rhythm to disturb yet. Day and night patterns in sleep, melatonin and cortisol develop over the first months of life (Rivkees, 2003). What parents experience on those trips is a feeding and handling problem rather than a clock problem.

From toddler age onward the same light rules apply, at a smaller scale. The parent site of the American Academy of Pediatrics suggests moving a child's sleep schedule two to three days before departure and getting them outdoors or into bright indoor light during local daylight after arrival.

Melatonin for children is where the guidance turns cautious. The American Academy of Sleep Medicine asks parents to speak to a paediatric professional before giving it (Rishi et al., 2023). Melatonin ingestions reported to United States poison control rose 530% between 2012 and 2021 (Lelak et al., 2022). A laboratory test of 25 melatonin gummies found only three of them within 10% of the label, one with no melatonin at all but 31.3 mg of CBD, and the rest between 74% and 347% of the stated dose (Cohen et al., 2023). In Britain melatonin for a child is a specialist decision. If you are considering it for a child, that is a conversation with your paediatrician rather than a shopping decision.

The plan for my next flight

Short trips first: under three days I stay on Munich time, book meetings inside my home daytime and accept that I am not much use in the evening. Nothing about a two day trip justifies moving a clock twice.

For the long ones, the sequence is short enough to keep on a phone note. Three days out, sleep and wake one hour earlier per day for an eastward flight, one hour later for a westward one. On the plane, set the watch to destination time and sleep on the destination night rather than on the meal service. On arrival, calculate the pivot, put the light windows in the calendar, keep naps under half an hour, stop caffeine eight hours before target bedtime and skip the alcohol. If you want the deeper background on sleep timing itself, the sleep guide and the guide on sleepmaxxing cover the parts that apply at home too.

For my return from New York it comes down to one line in the calendar, the same one the planner prints: sunglasses until 10:00 Munich time on day one, then outside from 10:00 to 14:00, every day one hour earlier.

Fun fact nobody needs: I never wear sunglasses otherwise, because I think they make you look full of yourself. For the hours before my temperature low I make an exception.

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_Canonical: https://longevity-germany.com/en/articles/jet-lag · Part of Longevity Cities · Updated 2026-08-20_