People who are totally blind don't sleep too well at night. Their body clocks go awry because they can't sense any light, so they can't tell night from day. Now researchers have found a treatment: the anti-jet-lag hormone, melatonin.

"Light is the major time cue in humans," says Debra Skene of the University of Surrey in Guildford. In sighted people with normal body clocks, levels of melatonin in the blood peak at around 4 am. In totally blind people, melatonin peaks at a different time each day. Their sleep suffers, so they often nap during the day to compensate for their disturbed nights.

Skene wondered if the body clock of completely blind people could be reset with daily doses of melatonin. In an experiment on seven totally blind volunteers with severe sleep disruption, she found that the melatonin treatment gave most a better night's sleep, with fewer daytime naps.

Later she found that the treatment only reset the clock if it was timed correctly in relation to the subject's own melatonin peak. "Melatonin can work, but we need to know the status of the clock before we begin treatment," she says.

New Scientist, September 16, 2000