Namedropper that I am, I need to mention that the lead researcher, Charles Czeisler, was a friend of mine in college whose career of preeminence in the biology of sleep regulation and circadian rhythms I have followed with interest. The value of melatonin as a sleep aid has long been equivocal, which I think has two explanations. First, since it is sold as a dietary supplement rather than a medication, there is no quality control about the dosage or bioavailability of the active ingredient in the melatonin you buy.

Secondly, the way it works essentially involves resetting your internal clock, telling your body it is time to go to sleep. Quite simply, melatonin will not be of much use helping a person whose sleep difficulty does not relate to a circadian rhythm problem. The current study, in which thirty-six healthy participants spent three weeks living in soundproof rooms with no time clues and were put on a 20-hour sleep-wake cycle in place of the usual 24-hour cycle, showed melatonin’s efficacy in re-entraining the body’s sleep schedule. This has most relevance to shift-workers who sleep during the daylight hours and to jetlagged travellers out of synch with their new timezones, situations in which I have recommended melatonin in the past.