Jet lag is a temporary sleep disorder that follows fast travel across several time zones. The body’s internal clock keeps running on home time while the sun, meals and alarm clocks at the destination say something else. The mismatch fades on its own, but the right timing of light, sleep and caffeine can cut the adjustment period by days.
How the body clock works
Almost every cell in the body follows a circadian rhythm, a cycle of roughly 24 hours that governs sleepiness, body temperature, hormone release and digestion. The master clock sits in the suprachiasmatic nucleus (SCN), a small cluster of nerve cells in the hypothalamus just above the point where the optic nerves cross. It keeps the clocks in the liver, gut and muscles in step.
The SCN resets itself every day, and its strongest time cue is light reaching the eyes. In the evening, as light fades, the pineal gland releases melatonin, the hormone that signals biological night. Meals, exercise and social contact act as weaker cues. After a long flight, all of these signals arrive at the “wrong” time, and the internal clocks drift out of step with each other and with local time.
Typical symptoms
- Trouble falling asleep at local bedtime, or waking at 3 or 4 a.m. and staying awake
- Heavy sleepiness in the afternoon or early evening
- Poor concentration, slower reactions and a short temper
- Stomach upset, constipation or loss of appetite at local mealtimes
- A general feeling of being unwell
Symptoms usually start within a day or two of arrival. A common rule of thumb is that the body adjusts by about one time zone per day, so a six-hour shift can take close to a week to settle completely.
Jet lag or travel fatigue?
Long flights also cause plain travel fatigue: dry cabin air, cramped seats, noise and stress. Travel fatigue affects any long trip, even a north–south flight within the same time zone, and it clears after one full night of sleep. Jet lag persists for several days and follows a pattern tied to home time. If a good night’s sleep solves the problem, it was travel fatigue.
Why flying east is harder
The human body clock runs slightly longer than 24 hours in most people, so it is easier to stay up later than to fall asleep earlier. Westbound travel asks the clock to delay, which comes naturally. Eastbound travel asks it to advance, which is harder: a traveler from Chicago arriving in Paris has to fall asleep at what feels like 4 p.m.
Not everyone is affected equally. Older adults tend to recover more slowly, and people who keep a rigid sleep schedule at home often notice the shift more. Children adapt reasonably well when meals, naps and bedtime move to local time right away.
Before the flight
- Shift gradually. Two or three days before departure, move bedtime and wake-up time by about one hour per day: earlier for eastbound trips, later for westbound trips.
- Move light with it. Before an eastbound trip, get bright light early in the morning; before a westbound trip, stay in bright light later in the evening.
- Start rested. Arriving with a sleep debt makes every symptom worse. Avoid a late packing night before departure.
On the plane
- Set the phone and watch to destination time when boarding and plan sleep around it.
- On an overnight eastbound flight, sleep as early as possible; an eye mask, earplugs or noise-canceling headphones help.
- Drink water regularly. Alcohol and caffeine both fragment sleep in the air and after landing.
- Walk the aisle and stretch every hour or two when awake.
After arrival: light, sleep and meals
Use light at the right time
Timed light exposure is the most effective tool against jet lag.
| Direction | Seek light | Avoid bright light | Sleep |
|---|---|---|---|
| Eastbound (clock must advance) | Late morning and midday outdoors | Early morning for the first day or two after big shifts, and late evening | Go to bed at local time, even if not sleepy |
| Westbound (clock must delay) | Afternoon and early evening | Very early morning | Stay up until a normal local bedtime |
Keep naps short
A nap of 20 to 30 minutes before mid-afternoon eases sleep pressure without stealing night sleep. A three-hour “arrival nap” feels good but anchors the body clock to home time.
Eat on local time
Meals at local times give the liver and gut clocks a signal of their own. A regular breakfast on the first morning helps more than grazing at odd hours.
Caffeine and melatonin
Caffeine does not reset the body clock, but it helps with alertness on the first days. A cup of coffee or tea in the local morning is useful; stop in the early afternoon so it does not delay sleep. The FDA cites 400 mg per day, about four cups of brewed coffee, as an amount not generally linked to harmful effects in healthy adults.
Melatonin is the one supplement with reasonable evidence for jet lag. The CDC’s travel guidance mentions doses of 0.5 to 5 mg taken near the local bedtime, and it is used most often for eastbound trips across five or more time zones. In the United States melatonin is sold as a dietary supplement, not as a regulated drug, so the actual dose in a tablet can vary. Anyone who takes other medications, is pregnant, or has a chronic illness should ask a doctor or pharmacist first. Prescription sleeping pills can shorten the first nights but do not move the body clock.
Two example trips
New York to London
London is five hours ahead of New York. A typical evening departure lands around 7 a.m. local time.
- In the two nights before the trip, go to bed 30 to 60 minutes earlier each night.
- Sleep on the plane as soon as the meal service ends.
- After landing, stay awake. Spend time outside before and around noon.
- Limit any nap to 30 minutes, and go to bed around 10 or 11 p.m. local time.
- Expect the first two or three days to be the roughest.
Los Angeles to Tokyo
Tokyo is 16 or 17 hours ahead of Los Angeles, depending on daylight saving time. The body can treat this as a delay of seven or eight hours instead, which is easier than a huge advance.
- In the days before departure, go to bed a little later each night.
- Most flights land in the afternoon. Stay outside in the daylight and stay up until a normal local bedtime.
- Plan light activities for the first two or three days and important meetings later in the week.
Short trips
For a stay of one or two days, adjusting may not be worth it. Keeping home time for sleep, and scheduling meetings for hours that match the home clock, often works better than a partial shift that has to be reversed on the way back.
Pilots, flight attendants and frequent flyers
Crews crossing time zones every week never fully adjust, and repeated disruption adds up. For that reason, the FAA limits flight duty periods and sets minimum rest times for airline pilots. Frequent flyers can borrow the crew approach: protect a fixed sleep window, use strategic naps, and avoid alcohol as a sleep aid.
When to see a doctor
Jet lag should fade within a week or two. Sleep problems that last longer, extreme daytime sleepiness, or a preexisting condition such as insomnia, sleep apnea, diabetes or epilepsy that is affected by irregular sleep are reasons to talk to a physician or a sleep medicine specialist. People who take medication on a fixed schedule, such as insulin or oral contraceptives, should plan the timing with a doctor or pharmacist before the trip.
Frequently Asked Questions
How long does jet lag last?
Roughly one day for each time zone crossed, often longer after eastbound flights. Most people feel clearly better after two or three days.
Is it better to sleep on the plane?
It depends on arrival time. On an overnight flight that lands in the morning, sleeping on board helps. On a daytime flight that lands in the evening, staying awake makes it easier to sleep at local bedtime.
Does melatonin work for everyone?
No. Studies show a benefit for many travelers, especially on eastbound trips, but the effect varies. Timing matters more than a high dose.
Can jet lag be avoided completely?
Rarely on long trips. Gradual pre-trip shifting, timed light and short naps can make it mild and short.
