Your article on melatonin (vol 6 no 11) was interesting and well researched, but not up to your usual high standards. First, let me declare my bias and vested interests. I have been interested in light effects on health for some years now, wrote a book about the subject back in the 80s, and have an involvement with a business producing full spectrum lights. I was one of the first in this country to recognize the potential of melatonin and attempt to integrate it into nutritional practice.

Your article reviews some of the evidence of a beneficial effect from melatonin, but only some. What about the dramatic effects on behaviour and sleep patterns, and in some cases the seizure frequency, of autistic and other developmentally disabled children? What about melatonin's supportive/regulatory effect on the immune system in general?The reality is that so many studies have been done now that they do provide accumulating evidence of safety not conclusive, granted, but comparable to what is done formally on most drugs.

As for its effects on fertility, melatonin seems to work differently in every animal studied, depending on their seasonal and hibernatory habits in some it triggers fertility, in others it inhibits it. In humans, it looks as though melatonin is the Fat Controller of fertility (female, at least).

Melatonin is unlike ovarian, adrenal or even pituitary hormones in that the pineal is constantly being influenced by the light levels to which we are exposed. In becoming industrialized, urbanized, indoor people who rarely see bright light or experience real darkness, we have already interfered substantially with our sleep/wake, melatonin production cycle; taking melatonin supplements would be a step towards normalizing this.

In theory, restricting melatonin to prescription only would be a reasonable safeguard on what is, admittedly, an emerging treatment. Damian Downing, co-editor, Journal of Nutritional and Environmental Medicine, London.......

WDDTY replies: We agree that melatonin may be a good idea for people with established illness, but as every attempt at throwing hormones at people with normal levels of them has proved disastrous in medicine (see our cover story this month), we tend to take a cautious view about all purpose miracle drugs.