Staying Healthy

How to reset your internal clock to combat jet lag

A few simple measures can help minimize the sleep disturbances and malaise that can occur when you cross several time zones.

internal clock jet lag
Image: faithiecannoise/iStock

This month we perform the annual ritual of turning back our clocks as Daylight Savings Time ends. Most of us can handle the one-hour time change easily. However, when we travel long distances across several time zones, few of us can survive the trip without feeling a little out of whack. For holiday travelers flying from coast to coast or overseas, recovering from the symptoms of jet lag—fatigue, insomnia, digestive upsets, and headaches—can consume a day or two of precious vacation time. According to Dr. Charles A. Czeisler, director of the Division of Sleep Medicine at Harvard Medical School, jet lag is due to a misalignment between the external environment and the internal clock in the brain that drives our daily performance, alertness, and the ability to sleep.

What happens during jet lag

Minimizing jet lag

If your destination is only a zone or two away, you may need to make only minor adjustments, like eating meals, going to bed, and awakening a little earlier or later than usual. If you're crossing several time zones, you may want to try the following:

Gradually switch to the new time. For several days before you leave, move mealtimes and bedtime incrementally closer to the schedule of your destination. Even a partial switch may help.

Stay hydrated. During the flight, drink plenty of fluids, but not caffeine or alcohol. Caffeine and alcohol can dehydrate you, which worsens the symptoms of jet lag. They can also disturb your sleep.

Switch your bedtime as rapidly as possible after arrival. Don't turn in until it is bedtime in the new time zone.

Use the sun to help you readjust. If you need to wake up earlier at your destination, get out in the early morning sun. If you want to rise later than you do at home, wait to go out in the sun until late in the afternoon.

plate dinner clock

A quick fix for jet lag?

In 2009, Dr. Clifford Saper and colleagues at Harvard-affiliated Beth Israel Deaconess Medical Center identified a second "master clock" in mice that can regulate circadian rhythms when food is scarce. In essence, the body's circadian rhythms are suspended to conserve energy.

It's been theorized that humans may have a similar mechanism and that a brief fast may trigger a quick reset of circadian rhythms. Dr. Saper has suggested a 12-hour to 16-hour fast the day before and during travel. For example, if you were to take a flight from New York City to Honolulu, you would refrain from eating for couple of hours before take-off and during the flight, but would have a good meal as soon as convenient after landing. This technique hasn't been tested in clinical trials, but there are many testimonials in the media to its effective-ness.

If you want to try this, it's a good idea to check with your clinician to see if it's advisable for you. And you will still need to drink water—not caffeinated beverages, juice, or alcohol—during your flight.


To continue reading this article, you must log in.

Subscribe to Harvard Health Online for immediate access to health news and information from Harvard Medical School.

  • Research health conditions
  • Check your symptoms
  • Prepare for a doctor's visit or test
  • Find the best treatments and procedures for you
  • Explore options for better nutrition and exercise
Learn more about the many benefits and features of joining Harvard Health Online »

I'd like to receive access to Harvard Health Online for only $4.99 a month.

Sign Me Up

Already a member? Login ».


As a service to our readers, Harvard Health Publishing provides access to our library of archived content. Please note the date of last review or update on all articles.

No content on this site, regardless of date, should ever be used as a substitute for direct medical advice from your doctor or other qualified clinician.

Free Healthbeat Signup

Get the latest in health news delivered to your inbox!

Sign Up
Harvard Health Publishing Logo

Thanks for visiting. Don't miss your FREE gift.

The Best Diets for Cognitive Fitness, is yours absolutely FREE when you sign up to receive Health Alerts from Harvard Medical School

Sign up to get tips for living a healthy lifestyle, with ways to fight inflammation and improve cognitive health, plus the latest advances in preventative medicine, diet and exercise, pain relief, blood pressure and cholesterol management, and more.

Harvard Health Publishing Logo

Health Alerts from Harvard Medical School

Get helpful tips and guidance for everything from fighting inflammation to finding the best diets for weight loss...from exercises to build a stronger core to advice on treating cataracts. PLUS, the latest news on medical advances and breakthroughs from Harvard Medical School experts.

BONUS! Sign up now and
get a FREE copy of the
Best Diets for Cognitive Fitness

Harvard Health Publishing Logo

Stay on top of latest health news from Harvard Medical School.

Plus, get a FREE copy of the Best Diets for Cognitive Fitness.