JOHN YDSTIE, Host:
NPR's Richard Knox reports.
RICHARD KNOX: First, let's get straight on how not to take melatonin, according to the new study.
CHARLES CZEISLER: Melatonin taken at the typical time most people take melatonin, which is before nighttime sleep, did not improve their sleep. And that's probably why melatonin has a mixed reputation.
KNOX: To determine when a melatonin pill does work to improve sleep, Czeisler and colleagues locked 36 healthy young volunteers, one at a time, in a windowless, soundproof room, away from all contact with the outside world, for 21 days. Then they used light and darkness cycles to really screw up their circadian clocks.
CZEISLER: We shifted the person's timing of when they slept four hours earlier. It would be like traveling from Anchorage to New York and making that kind of a shift every day, traveling further and further eastward and going around and round the globe.
KNOX: This was necessary to separate melatonin's role as a re-setter of people's biological clocks from its function as a sort of reverse alarm clock that signals time to sleep. When the study subjects took even a tiny dose of melatonin during the time when their natural melatonin levels were low, that is, when their bodies thought it was daytime, they slept better.
CZEISLER: If we increase blood levels of melatonin during the daytime, when the body doesn't release melatonin, we do improve the ability of participants to sleep during the daytime.
KNOX: Their sleep efficiency improved. That's the amount of time they actually slept while they were in bed.
CZEISLER: Our study shows that if they were taking melatonin when they were attempting to sleep during the daylight hours, they'd get an extra half an hour of sleep.
KNOX: Dr. Thomas Roth says a half hour more sleep is a big deal.
THOMAS ROTH: It's very important to understand, sleep loss is cumulative.
KNOX: Roth is a leading sleep researcher at Henry Ford Hospital in Detroit. He says people generally run up a sleep deficit during the workweek.
ROTH: Most of us, because we lose about a half hour of sleep a night, sleep longer on weekends.
KNOX: But for those who want to act on these findings, there's a problem. There's no way to tell whether the bottles of melatonin you buy in the drugstore or health food store actually contain any melatonin.
ROTH: By and large, the products in health food stores are not governed by anybody. There's no agency which sort of defines what's in there.
KNOX: Richard Knox, NPR News, Boston. Transcript provided by NPR, Copyright NPR.
