Melatonin supplements may promote daytime sleep

By Charnicia Huggins

NEW YORK (Reuters Health) - Melatonin, a hormone involved in the regulation of the sleep/wake cycle, may help night shift workers get more rest during daylight hours, according to the findings of a small study published in the journal Sleep. Melatonin, which is released by the brain primarily during the hours of sleep, is also available as an oral supplement.

"If for reasons of being a shift worker or due to travel across time zones you have to sleep at a strange hour, this is precisely when taking melatonin will help you fall asleep faster and stay asleep longer," lead investigator Dr. James K. Wyatt, of Rush University Medical Center in Chicago, told Reuters Health.

"The findings really point out how important our brain's 24-hour clock, also called the circadian system, is to being able to remain awake and alert throughout the day (and) how the circadian system can therefore get in the way of attempts to sleep during the day."

Other researchers have investigated whether melatonin improves sleep when taken before daytime naps or before normal nighttime sleep. Some studies have reported positive findings, but most of them had significant limitations, such as very short study periods or a lack of female study participants, which limited the extent to which the findings could be generalized.

Wyatt and his colleagues at Harvard Medical School in Boston conducted a month-long study of the sleep-facilitating effect of melatonin. The study included 21 men and 15 women between 18 to 30 years old, who were healthy and free of any sleep disorders.

The subjects' normal sleep/wake patterns and melatonin production were observed for 3 days. They were then put on a 20-hour sleep-wake schedule, "simulating a traveler crossing four time zones eastward every day," study co-author Dr. Charles A. Czeisler, now at Rush University Medical Center in Chicago.

The study participants took 0.3 or 5 milligrams of melatonin or a look-alike placebo pill 30 minutes before each scheduled sleep period, which lasted about 7 hours. This schedule was maintained for about 3 weeks. The study was conducted in a private, windowless suite in a research center that was sound-isolated and had no windows or any other cues of the time of day.

Compared with the placebo group, sleep times were longer in the melatonin group during the hours of the day when the body does not normally produce the hormone.

"We believe melatonin is directly suppressing your body's 24-hour clock and in particular suppressing the circadian system's drive for wakefulness...in some ways dampening that wake-up signal," Wyatt said. However, when melatonin was taken during the nighttime hours, when the body usually produces its own melatonin, no additional benefit was observed.

It appears to be a chase in which "more is not better," Wyatt said. "If you're trying to sleep when your body wants you to, taking a pill of melatonin will provide no additional benefit."

"Even when given melatonin, daytime sleep still falls short of the quality and quantity of nighttime sleep," Wyatt added. "Humans are just biologically designed to sleep at night," he added.

SOURCE: Sleep, May 1, 2006.