The Massachusetts Institute of Technology (MIT), where the research was carried out, said that the findings could "jump-start interest in the dietary supplement".
Melatonin is a natural, soporific hormone secreted by the pineal gland during the hours of darkness. Melatonin supplements are widely available in the United States and are reported to induce sleep and ameliorate disturbed sleep patterns - both intrinsic and due to extraneous circumstances such as shift work or jet-lag.
Exogenous melatonin reportedly induces drowsiness and sleep, and may ameliorate sleep disturbances, including the nocturnal awakenings associated with old age.
Professor Richard Wurtman, director of MIT's Clinical Research Center, led the meta-analysis of 17 peer-reviewed papers on the effects of melatonin with the aim of determining conclusively whether or not melatonin supplementation works.
"A meta-analysis essentially tells 'yes' or 'no' that a treatment does or does not have a significant effect," said Wurtman.
His conclusion was a resounding "yes" - a result which he claims means there should no longer be any controversy about whether melatonin works.
The meta-analysis assessed the difference between the response on placebo and the mean response on melatonin for each of the studies, all of which were placebo-controlled and included objective measurements on at least six adults. It showed that exogenous melatonin significantly reduced sleep onset latency by 4.0 min, increased sleep efficiency by 2.2 percent, and increased total sleep duration by 12.8 min.
Taken individually, the 17 studies produced heterogeneous data, which Wurtman suggests were due to differences in doses, quality, excipients and purity of the supplements used.
The data have contributed to widespread skepticism over melatonin's efficacy, coupled with the risk of serious side effects, including hypothermia, associated with taking too much of the hormone.
Most commercially available supplements contain doses of around 3mg, which is, according to Wurtman, ten times the effective amount.
In a study published in the Journal of Clinical Endocrinology and Metabolism in October 2001, Wurtman and colleagues showed that only around 0.3mg of melatonin is needed to help adults fall asleep and return to sleep after waking up during the night.
He maintains that a higher dose taken over several days can actually block the beneficial effects, as the brain's melatonin receptors become unresponsive when exposed to excess quantities, and cause some people to experience hangover-like symptoms during the day.
Following the 2001 study, Wurtman patented the use of melatonin in doses up to 1mg and has since licensed the work to Nature's Bounty for its 1mg supplement.