Jet lag and your body clock: sleep, light and staying well on long trips

This page is general information for travelers, not medical advice. If you have a health condition, or questions about your own sleep or health, talk to a health care provider.

You land after a long flight, the sun is shining and the city is waking up, but your body insists it is the middle of the night. Hours later, just as everyone else goes to bed, you are wide awake. That mismatch is jet lag, and it comes from a clock inside you that does not change time zones as quickly as an airplane does.

The body clock

The human body runs on a daily cycle. The National Heart, Lung, and Blood Institute describes an internal circadian clock that cycles about every 24 hours and tells you when it is time to sleep or wake. It explains that the body tries to align this sleep–wake cycle to cues from the environment, such as when it gets light or dark outside, when you eat and when you are physically active.

The National Institute of General Medical Sciences adds that light and dark have the biggest influence on circadian rhythms, though food intake, stress, physical activity, social environment and temperature also affect them. Its fact sheet lists body functions these rhythms influence, including sleep patterns, hormone release, appetite and digestion, and temperature, and notes that travel between time zones alters them. A 2010 review in Nature and Science of Sleep, on jet lag syndrome and circadian organization, describes the suprachiasmatic nucleus of the hypothalamus as containing the master network that coordinates these daily rhythms.

What jet lag is

Wikipedia's article on jet lag describes it as a temporary physiological condition that occurs when a person's circadian rhythm is out of sync with the time zone they are in, typically after traveling rapidly across several time zones east or west. The same article points out that a long flight mainly north or south, without crossing time zones, does not cause jet lag, though general travel fatigue from a cramped seat, dry air and disrupted routine can still leave you tired.

Direction matters too. A 2012 review in Sports Health, on jet lag in athletes, reports that symptoms of jet lag and sleep disturbance are worse after eastward flights than after westward ones, and that there is strong evidence that mood and cognition are adversely affected by jet lag. For most travelers that simply means: expect a flight east to feel harder, and plan the first days accordingly.

What travelers commonly do

There is no single trick that makes jet lag disappear, and none of the habits below is a guaranteed fix. They are simply the ordinary, common-sense things many travelers do to help their days line up with the new place sooner:

• Shift bedtime gradually before leaving. Some travelers move their sleep a little earlier or later in the days before a trip, in the direction of the destination.
• Seek daylight at the destination. Since light is the strongest cue for the body clock, many people spend time outdoors in daylight soon after arrival.
• Keep meals and sleep on local time. Eating and going to bed at the local hours, rather than the hours of home, gives the body consistent cues.
• Drink water and move about on the plane. Dry cabin air and long hours of sitting add to general travel fatigue. Stretching and walking the aisle when it is safe to do so help many people feel better on arrival.
• Plan a gentle first day. Leave important meetings, long drives and demanding hikes for later in the trip.

Sleep on the road

Good sleep is harder to come by in unfamiliar rooms. MedlinePlus's page on healthy sleep describes sleep as a natural process that helps the body regain energy and supports learning and memory, and notes that the quality of sleep matters as well as the number of hours. It suggests relaxing before bed and getting rid of distractions such as screens. On the road, that might mean a quiet evening routine, a dark room and a steady bedtime once you have arrived.

The body at altitude

Long-haul trips sometimes end high in the mountains, and altitude brings its own effects. MedlinePlus's encyclopedia entry on acute mountain sickness describes an illness that can affect climbers, hikers, skiers and travelers at high altitudes, caused by reduced air pressure and lower oxygen levels. It describes gradual ascent as the best way to prevent altitude illness and states that the main treatment for all forms of mountain sickness is to descend to a lower altitude. A 2017 review in the European Respiratory Review, on acute high-altitude illness, describes three forms: acute mountain sickness, high-altitude cerebral edema and high-altitude pulmonary edema.

Jet lag usually settles as your body adjusts to the new time zone. But sleep trouble that carries on after you are home is worth raising with a health care provider, and at altitude, symptoms such as a worsening headache, breathlessness while resting, confusion or unsteadiness are reasons to stop climbing, go down, and see a health care provider. MedlinePlus advises contacting a provider about symptoms of acute mountain sickness, even if you felt better after returning to a lower altitude.

Heat and staying well in general

Travel puts the body through changes of food, water, climate and routine all at once. MedlinePlus's traveler's health page notes that once you arrive, it takes time to adjust to the water, food and air in another place, and it collects official guidance on staying healthy before and during a trip. In hot places, heat adds its own risks; the guides to the Grand Canyon and the Nevada desert cover that side of things.

Plan for the first days

The most useful thing you can do about jet lag is to expect it. Build slack into the start of a trip, keep plans light, and let the new place set your rhythm. Long train journeys can ease the change even more gently; the train travel tips and the guide to packing smart are good companions for a long trip.