For example, a new slow-release version of caffeine may help you stay awake during the day, but it may also keep you up at night. And melatonin may help you sleep at night, but it won't keep you from dozing off in daytime hours.
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Mixed Blessings for Jet Lag
In the study, researchers tested the effects of slow-release caffeine and melatonin on three groups of nine U.S. Air Force Reservists. Each of the men and women typically went to bed between 11 p.m. and midnight and slept about 6.5-7.5 hours.
For five days, the reservists had identical routines at their Texas base. Then they boarded a plane for France and were not allowed to sleep during the flight, which crossed seven time zones.
Each group received either slow-release caffeine (300 mg at 8 a.m.), 5 mg of melatonin starting the evening before the flight and for the next four evenings, or a placebo.
Researchers found both drugs had positive effects in relieving some common symptoms of jet lag after an eastbound flight.
The slow-release caffeine helped alleviate daytime sleepiness, but it also had some unwanted side effects by reducing the quality of nighttime sleep.
In contrast, melatonin users experienced better quality sleep but still felt sleepy during the day.
The results appear in the January issue of the Journal of Applied Physiology.
Researchers say some of the beneficial effects of the drugs may have been reduced because the participants were deprived of sleep during the flight. They say more studies are needed to fully understand the effects of these drugs in relieving jet lag.