JUNE 25, 03:15 EDT

Study Sheds New Light on Insomnia

By PAUL RECER
AP Science Writer

WASHINGTON (AP) — The brain clock that regulates sleep works as accurately for the old as for the young, suggesting that many theories about insomnia among the aged are flawed, according to a study published today.

``We are going to have to rethink all of the explanations we have been giving for insomnia,'' said study lead author Dr. Charles A. Czeisler of Harvard Medical School and Brigham and Women's Hospital in Boston.

Among other major findings appearing today in the journal Science is that the brain clock regulating sleep is on a 24-hour schedule, not the 25-hour cycle that researchers have long believed was unique to humans.

``All of the textbooks indicate that humans have a 25-hour day instead of a 24-hour day. We now know that is wrong,'' said Czeisler.

Andrew A. Monjan, chief of neurobiology at the National Institute of Aging, said the new study changes fundamental assumptions about the causes of sleeplessness among the elderly and will prompt researchers to find new solutions for a sleep disorder that affects more than 10 million elderly Americans.

``We know now that poor sleep is not a function of being old by itself,'' said Monjan. ``We also know now that you don't treat insomnia by just taking a sleeping pill.''

Researchers need to look at such things as exposure to room light, illness and genetics to explain why insomnia has become a troublesome part of the lives of millions of people, particularly the elderly, Monjan said.

Richard E. Kronauer of Harvard University, a senior author of the study, said the research emphasized how exposure to artificial light during nighttime hours can reset the body's sleep clock, making it difficult to get up on time in the morning.

``We have been finding that people young and old are more sensitive to light than we suspected,'' said Kronauer. ``Light in the evening is a strong influence on shifting the clock toward a later time.''

The tendency of many sleepless people to push bedtime later and later, particularly on the weekends, has been blamed on what researchers thought was a natural adjustment to the cumulative effect of a 25-hour brain clock.

Since the new study shows the clock is actually 24 hours, researchers now think exposure to light is a much more important factor than previously believed in resetting the clock and disrupting sleep.

In the study, two dozen men and women endured a month of living in subdued light, with no clues to the passage of time, while researchers monitored body chemistry and temperature that mark the action of the body clock. Eleven of the subjects were young men, with an average age of 23.7 years, and 13, nine men and four women, were older, with an average age of 67.4 years.

The subjects were placed on a 28-hour cycle, so their wake-sleep cycle was four hours longer than the rest of the world's. Czeisler said this elongated cycle disconnected the patients' natural clocks from outside influences that usually control a person's day, such as work or school schedules.

The researchers measured changes in temperature and chemistry to detect when the body clock, or circadian pacemaker, turned on. Earlier studies had shown that the clock is centered in the brain's hypothalamus. For most people, the impulse to sleep peaks around 10 p.m. when the body temperature starts dropping. The temperature rises at about 4 a.m., increasing the chances of awakening, but two hormones, melatonin and cortisol, help the body remain asleep for the rest of the night.

Czeisler said the measurements showed that the human sleep clock operates on a schedule of 24 hours, 11 minutes, not the 25 hours earlier studies had shown. It also showed that for people over 65, the clock ticked at almost exactly the pace of people in their 20s.

Studies that concluded humans were on a 25-hour cycle may have been affected by light exposure, Czeisler said. Even though earlier researchers used elaborate precautions to avoid outside influences, test subjects routinely used strong artificial lights, he said.

``Light is the most powerful synchronizer of the biological clock,'' said Czeisler. When test subjects in the earlier studies switched on lights, it was ``giving them the equivalent of a drug that reset the clock. That's what resulted in the apparent 25-hour period that is published in textbooks.''

Exposure to light pushes forward the body's schedule for releasing melatonin and cortisol, said Kronauer. When these hormones are released at the wrong time, it can arouse a person in the middle of the night or cause drowsiness during the day.

Study Sheds New Light on Insomnia

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