Cambridge, Massachusetts, USA —
An analysis of melatonin studies has upheld the controversial supplement's effectiveness as a sleep aid. 
The analysis, which included 17 peer-reviewed scientific papers, was aimed at determining whether supplements of the hormone can improve sleep among insomniacs, older adults and others. 
"A meta-analysis essentially tells 'yes' or 'no'—that a treatment does or does not have a significant effect," says Richard Wurtman of MIT, the study's principal investigator. "When a meta-analysis says 'yes,' there should no longer be any controversy about whether the treatment works." 
Previous studies by Wurtman and colleagues showed that small doses of melatonin, about 0.3 milligrams, are necessary for restful effects. The researchers found, however, that commercially available melatonin pills can contain 10 times the effective amount. 
At that dose, says Wurtman, the hormone's effects end after a few days because melatonin receptors in the brain become unresponsive when exposed to too much of the hormone. 
Such inadvertent overdosing, say the researchers, has contributed to controversy over melatonin's efficacy. 
But the new meta-analysis shows that melatonin does indeed have positive effects on sleep—even though some of the analyzed studies also involved high doses of the hormone. 
The research is reported in the journal Sleep Medicine Reviews.

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Controversial melatonin supplements confirmed as sleep aid