"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.
The study in the journal Science also found 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.
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 -- also known as the circadian pacemaker -- making it difficult to get up on time in the morning.
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.
"We have been finding that people young and old are more sensitive to light than we suspected," said Kronauer.
Since the new study shows that the brain clock actually runs 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. Almost half of the subjects (11 men) were an average age of 23, while the rest (nine men and four women) were an average age of 67-years-old.
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 schedules.
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., icreasing the chances of awakening, but the body's sleep hormones help the person to remain asleep for the rest of the night.
Czeisler said the measurements of the subjects' temperature and chemistry 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.
Written By Paul Recer