Both bright light and melatonin have successfully been used in laboratory and field settings to "phase advance" (resetting the circadian clock earlier in time so that all the circadian rhythms of the body occur earlier) thereby helping people adapt to night shift work or to a new time zone following rapid transmeridian jet travel. Melatonin alone has been shown to synchronize the circadian clock of the blind to the 24-hour day.
"However, this is the first study to show that melatonin and bright light can both help to advance the circadian clock, and the combination of bright light and melatonin produces a larger phase advance than bright light alone," said Senior Author Charmane Eastman, Ph.D., Director of the Biological Rhythms Research Lab and Professor of the Behavioral Sciences Department at Rush University Medical Center in Chicago. Phase advance is the resetting of the circadian clock earlier in time so that all the circadian rhythms of the body occur earlier.
Dr. Eastman and colleagues at Rush's Biological Rhythms Research Lab studied 44 healthy adults -- 24 men and 19 women -- between the ages of 19 and 45 years old. The participants were randomly divided into three groups and assigned one of three treatments -- placebo, 0.5 mg melatonin, or 3.0 mg melatonin.
Each participant was assigned a strict eight hour sleep schedule that was similar to their typical sleep schedule. In addition, they had to remain in bed, in the dark, trying to sleep throughout the eight hour scheduled sleep/dark period. On the seventh day, each person was given a baseline phase assessment, starting seven hours before and ending three hours after their beginning bedtime. They then slept in the lab and were awakened at their scheduled wake time. The participants continued on this sleep schedule through day 10 of the study.
Days 11 through 13 marked the treatment period of the study, during which the participants slept in the lab in individual, dark, temperature-controlled bedrooms. Each afternoon, each person received either 0.5 or 3.0 mg of melatonin or matching placebo. The study ended with a final phase assessment on day 14.
The researchers found that those given melatonin experienced significantly larger phase advances -- the 0.5 mg group at 2.5 hours and the 3.0 mg group at 2.6 hours versus the placebo group at 1.7 hours. Moreover, the participants did not experience jet lag-type symptoms. There was a slightly larger phase shift with the 3.0 mg dose compared to the 0.5 dose; however, the difference was not statistically significant. In addition, the higher melatonin dose made the participants slightly more sleepy in the evenings after taking the pill. Therefore, the researchers recommend using the 0.5 dose in combination with morning intermittent bright light to advance their sleep schedule.
"The findings are very practical," said Dr. Eastman. "A business person could go to a pharmacy and buy 0.5 mg of melatonin over the counter. He or she would also have to buy or rent a light box. Then before flying east, he or she could go to bed and wake up earlier each day while using the light box in the morning and taking melatonin in the evening. If they did this for the number of days equivalent to the number of time zones crossed, then they should be completely adjusted to the new time zone before they fly," she added. "However, even following the schedule for a few days before flying would reduce the jet lag experienced upon arrival at the destination. The more days a person follows this procedure the less jet lag they will have on landing and the sooner they will adjust and feel no jet lag."
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