Small doses of melatonin can help middle-aged and elderly insomniacs sleep better, American researchers say. People with age-related insomnia who took melatonin pills – available in health food stores in the United States – sleep better, said the team at the Massachusetts Institute of Technology.

New Zealand health officials banned over-the-counter sales of melatonin pills two years ago. They can be obtained only on prescription. The Health Ministry made the change when melatonin started selling well as a dietary supplement at health food stores. The ministry claimed importers and retailers had not been able to offer significant new evidence that melatonin was safe. But the hormone is still being used by New Zealand farmers in a pill called Regulin, to trick sheep into thinking day lengths are shortening and so trigger early lambing.

A lobby group, which included three importers, a New Zealand manufacturer and health food industry representatives said up to ten thousand New Zealanders had been using melatonin. They included many older people who wanted to regulate sleep patterns.

Irinia Zhdanova, a researcher at the department of Brain and Cognitive Sciences at MIT, tested 30 people over the age of 50. Some of whom had age-related insomnia. She gave them varying doses of melatonin or a dummy pill half an hour before they went to bed.

People who received the largest dose – 0.3mg – slept much better, she told a meeting of the Society for Neuroscience in Miami Beach. We hope our research will help people avoid potential short and long-term side effects from melatonin treatment," she said.

It could also identify people who might benefit from a melatonin supplement, as well as those who should be warned against increasing their melatonin levels."