Claims that the wonder supplement melatonin can slow the aging process have been based on faulty evidence, a leading expert has claimed.

Researchers had carried out tests on mice which had a genetic deficiency to make their own melatonin, so casting doubt on the findings.

These results have, nonetheless, fuelled a buying frenzy in the US for the supplement, which is usually produced naturally by the body during the night. Others have claimed the supplement can also cure Alzheimer's disease and AIDS, and can improve sexual and cardiovascular function, but there is no evidence to support these claims, says Prof J Arendt, an endocrinologist at the University of Surrey.

Side effects have also been reported, he points out in an editorial for the British Medical Journal. When melatonin has been taken as a contraceptive, usually at doses as high as 300 mg a day, side effects such as abnormal bleeding and headache have been reported.

He also puts a question mark over the claim that the supplement can inhibit cancer. While it has been found to slow cancer cells in test tubes, it has also increased melanoma growth in hamsters.

Questions of safety have still to be agreed, as have doses for different conditions. Melatonin is freely available in the US in health stores because it is classified as a food, and so does not require a special licence. It is available in the UK only on prescription (BMJ, May 18, 1996).

Insomniacs may be failing to produce sufficient melatonin naturally, researchers from Littlemore Hospital in Oxford, England, have discovered. They recruited 10 men and women with insomnia and monitored the melatonin in their blood during the evening and night, and found that they were producing up to 40 per cent less melanoma than people who sleep normally.

The researchers concluded that insomniacs may benefit from melatonin supplementation.

See WDDTY vol 6, no 11 for our special report on melatonin.