When you fly across several time zones, you ask your body to adjust to a new time and a new place. It takes awhile for the internal clock to reset itself to the new day or night cycle. That's why you get jet lag. And the more time zones you cross, the more you suffer.
No matter which way you're going, each time zone crossed requires about 1 day of adjustment, says Charles Ehret, Ph.D.
The previously mentioned inner body clock, says Dr. Ehret, is really a whole set of clocks controlled by a master clock. "Every cell in the body is a clock," he explains, "and they're all brought together by a special pacemaker in the brain."
Normally your body clock operates on cycles approximately 24 to 25 hours long. But rapid time changes disrupt all that. The result is jet lag—fatigue, lethargy, inability to sleep, trouble concentrating and making decisions, irritability, perhaps even diarrhea and a lack of appetite.
Though you can't make time stand still, there's a lot you can do to take some of the zap out of jet lag.
Charles Ehret, Ph.D., is a pioneer in the field of chronobiology, the study of time's effect on plants, animals, and people. He is a retired senior scientist from the Argonne National Laboratory, a unit of the U.S. Department of Energy.
Al Lewy, M.D., Ph.D., is a psychiatrist at Oregon Health Sciences University School of Medicine in Portland. He has done studies on the effects of sunlight on the human body clock.
Timothy Monk, Ph.D., D.Sc., is a professor of psychiatry and director of the human chronobiology research program at the University of Pittsburgh School of Medicine.
Marijo Readey, Ph.D., was formerly a researcher at the Argonne National Laboratory, a unit of the U.S. Department of Energy.