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Health A-Z

Medical Content Created by the Faculty of the
Harvard Medical School

What Is It?

Jet lag is a type of sleep disorder that is a reaction to traveling between time zones.

Our bodies naturally develop a sleep-wake cycle that is tied to the patterns of light and dark in our environment. This cycle, called the circadian rhythm, affects many body processes, including temperature and hormone levels.

Because traveling between time zones changes the light-dark patterns in your environment, it can disrupt your body's rhythms. A change of even a few hours may not seem significant, but often it is enough to affect the body's sleep-wake cycle. For example, a Californian who travels to New York may receive a wake-up call at 7 a.m., but his or her body still is running on California time, where it is only 4 a.m.

The effects of jet lag go beyond being tired for a few extra hours. Because the disruption in the sleep-wake cycle affects your body's hormone levels, many body processes can be thrown off balance, leading to a variety of symptoms.

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From Health A-Z, Harvard Health Publications. Copyright 2007 by the President and Fellows of Harvard College. All rights reserved. Written permission is required to reproduce, in any manner, in whole or in part, the material contained herein. To make a reprint request, contact Harvard Health Publications. Used with permission of StayWell.

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