Rapid responses are electronic comments to the editor. They enable our users to debate issues raised in articles published on bmj.com. A rapid response is first posted online. If you need the URL (web address) of an individual response, simply click on the response headline and copy the URL from the browser window. A proportion of responses will, after editing, be published online and in the print journal as letters, which are indexed in PubMed. Rapid responses are not indexed in PubMed and they are not journal articles. The BMJ reserves the right to remove responses which are being wilfully misrepresented as published articles.
Diabetics, and pre-diabetics, tend to have a great oxidative burden. Yet while melatonin has shown to have positive effects, such as antioxidant action, it also has deleterious effects, such as interfering with metabolic function, inducing hypertension, increasing mortality in animals, etc. (review http://www.supplements-and-health.com/tryptophan-side-effects.html ). Therefore, it may be that the relative lack of its antioxidant activity in the people with low levels elevated their risk of developing full-fledged diabetes.