Does melatonin improve sleep?

Editor—Buscemi et al in their meta-analysis report that melatonin is ineffective in treating secondary sleep disorders or sleep disorders accompanying sleep restriction such as jet lag or shift work.¹ The published reports in this domain certainly show some inconsistency, and now there is inconsistency in the meta-analyses.² Numerous published studies, mostly with a positive result, have not been included, even the first controlled jet lag trial, published in the BMJ.³

Buscemi et al may have done a disservice to people who do benefit from melatonin and may in consequence be denied access (in the United Kingdom) to this prescription-only medication. For example, the authors do not mention the importance of melatonin in blind sleep disorder and delayed sleep phase syndrome. Some of the data have appeared previously in a report from the Agency for Healthcare Research and Quality,³ where benefits for delayed sleep phase syndrome were identified.⁴

Figure 1.

Successful use of melatonin to counter the effects of a change in time zones or shift work requires correct timing of treatment relative to internal circadian rhythms. Incorrect timing can lead to undesirable effects. It is difficult to time melatonin correctly in field studies. Uncontrolled exposure to natural light (which shifts internal timing), individual differences, and unscheduled sleep times all contribute to the problems. If a reliable and rapid method for assessing the timing of the human internal clock (and hence the timing of treatment) were available no doubt the efficacy of melatonin would be enhanced.

A more helpful approach to assessing the usefulness of melatonin would be to evaluate those few studies where circadian timing was either measured or accurately predicted before treatment.