"Jet Lag and Melatonin: Timing is Everything"
by Jian M. Ding, MD PhD
Assistant Professor of Medicine and Neuroscience Program, University of Minnesota
Director, Chrono-neuro-immunology Lab, Minneapolis Medical Research Foundation
Inventions of the light bulb and airplane greatly enhanced human capability. However, they also imposed new challenges to human health. Travel across time zones and shift-working schedules are familiar examples. Jet lag is often associated with fatigue, daytime sleepiness, loss of appetite, difficulty concentrating, and inability to sleep at night. We experience these symptoms because the human body is genetically programmed to perform certain physiological functions only at certain times of the day. The variation of physiology around the 24-hour cycle is referred to as circadian rhythm, which is an important behavioral adaptation to the earth's daily rotation.
Circadian rhythms are not merely passive reflections of the environmental light-dark cycle, but instead depend upon an underlying endogenous clock. The suprachiasmatic nucleus (SCN) of the hypothalamus is the mammalian circadian clock that synchronizes the functions of different organ systems to each other and to the environmental light-dark cycle. In addition to the SCN, other structures also influence the human circadian rhythm. The retina is the dominant circadian clock in invertebrates, such as sea slugs. The pineal gland is the dominant circadian clock in birds. In mammals, these ancient circadian pacemakers work in concert with the SCN. Melatonin is a hormone synthesized in the pineal gland and released at night.
The circadian clock is responsive to environmental stimuli. While light is the most important regulator of the SCN, the time of food intake is more important in regulating the liver's circadian rhythm. Light can to a certain extent advance or delay the phase of the circadian rhythm depending on the time of the circadian cycle. Such advances and delays are referred to as phase shifts. Jet lag is the result of a phase shift of the circadian rhythm. Exposure to light during the early night delays the clock (westward traveling), whereas light exposure during the late night advances the clock (eastward traveling). Melatonin intake before bedtime advances the clock, whereas melatonin intake during the day delays the clock.
Many people have experienced that it takes a long time to recover from a jet jag. That is because resetting the circadian rhythm is a slow process. It takes 24 hours to reset the circadian rhythm of all the organ systems by one hour. Thus, it normally takes a week to recover from a 7-hr jet lag. Although no medicine or therapy can eliminate jet lag, appropriate use of light, melatonin, and mealtime can help speed up the process. For example, when traveling from Minneapolis to Paris (6 hr phase advance), taking melatonin (0.5 mg) the night before your flight will help advance the circadian clock by 1-3 hours. When traveling from Minneapolis to Japan (9 hr phase delay), drinking coffee (2 cups of espresso) the night before and taking melatonin (0.5 mg) in the morning will help delay the circadian clock by 1-3 hours. The purpose is to reset the circadian clock to the right direction even before you arrive in the destination. Once you arrive in the destination, try to get as much sunlight as possible during the day to entrain your circadian clock to the local time.
Lately, the effect of melatonin has been exaggerated by the media. Melatonin has no anti-aging or aphrodisiac effects. In fact, over the counter melatonin is sold as a food supplement, not as a drug. Thus, the purity and the exact amount of active ingredient on the label can not be assured. In addition, the dose of melatonin tablet in most commercial packages is way too large ranging from 3 mg to 5 mg. To adjust the circadian clock, 0.5 mg is more than sufficient. If you cannot find a pill with a small enough dose, break it apart.