Hormone Can Regulate Internal Clock

Thursday, October 12th 2000, 12:00 am
By: News On 6

Blind people often suffer insomnia and daytime sleepiness because they cannot see light and dark, the cues that set most people's internal clocks to a 24-hour cycle. But a study found that melatonin can re-set those clocks.

The study looked at seven blind men and women with circadian rhythms — the bodily changes that guide sleeping and waking cycles — of 24.2 to 24.9 hours.

Each person was given either a placebo or 10 milligrams of melatonin — a hormone produced deep in the brain by the pineal gland — an hour before bedtime for three to nine weeks. Then the people who had been taking the look-alike placebos got melatonin, and vice versa.

Nobody responded to the placebos, but six of the seven were able to re-set their clocks to 24 hours with melatonin.

They were able to keep the benefit when the dose was gradually reduced to 0.5 mg.

The study, published in Thursday's New England Journal of Medicine, was led by Dr. Robert L. Sack of the Sleep and Mood Disorders Laboratory at Oregon Health Sciences University.

An internal clock of 24.2 hours adds 12 extra minutes a day — minutes that add up quickly. After two months, a person would be 2 hours out of sync with the world, wide awake at midnight and struggling to keep his eyes open at noon. That would happen in only 13 or 14 days with a 24.9-hour cycle.

About 100,000 people, or half of the totally blind people in the United States, probably suffer from such ``free-running'' circadian rhythms, Sack said.

Melatonin also might help people with jet lag or those who routinely work at night or early in the morning, he said.

Doctors have so far managed to get very few people's sleep cycles on track with melatonin, Josephine Arendt of England's University of Surrey wrote in an editorial.

``The hype and the claims of the so-called miraculous powers of melatonin several years ago did a great disservice to a scientific field of real importance to human health,'' Arendt wrote.

``With these recent careful and precise observations in blind persons, the true potential of melatonin is becoming evident, and the importance of the timing of treatment is becoming clear. Our 24-hour society, with its chaotic time cues and lack of natural light, may yet reap substantial benefits.''


On the Net:

Oregon Health Sciences University sleep disorders home page: http://www.ohsu.edu/hosp-sleep/

American Federation for the Blind: http://www.afb.org