Daytime Sleep, Jet Lag
Scheer tells WebMD that while the benefits of taking melatonin for nighttime sleep are unproven, the hormonal supplement does appear to help shift workers and other people who need to sleep during daylight hours.
Melatonin is produced naturally by the brain's pineal gland at night to regulate sleep, but production goes way down during the day. Melatonin supplementation appears to trick the body into thinking that it is nighttime.
While the large review suggested that melatonin is not useful for jet lag, Scheer says that may only be half true. He says the supplement may help speed up the internal clock, helping to adjust to a new time zone. But it does not seem to be as effective in helping to readjust to one's original time zone.
So while taking melatonin may benefit a traveler who loses five hours flying from Boston to London, it probably won't help as much on the return trip.
"You would want to delay the onset of sleep when returning from London to Boston, and it appears that melatonin is not as effective for that," Scheer says.
Is Dosage the Key?
While the studies to date suggest that melatonin is only modestly effective for promoting nighttime sleep, all agree that the research is far from conclusive.
Massachusetts Institute of Technology neuroscientist Richard Wurtman, MD, is credited with discovering the sleep-inducing properties of supplemental melatonin back in the early 1980s. Wurtman served as principal investigator of the newly published review.
He tells WebMD that the research on melatonin and sleep is misleading because the dosages used in the studies were often too high.
Wurtman contends that the optimal dosage of melatonin is just 0.3 mg and that taking much higher doses causes the hormone to stop working within a few days. Commercially available melatonin preparations contain up to 10 mg of the hormone.
"People are getting doses of melatonin that raise [blood levels] of the hormone to up to 500 times what is normal," he says. "At that dosage it either stops working after a while or actually causes insomnia in some people."