Need a Lot of Sleep? Blame It on Body Clock

Published on Wed 17 Oct 2007

If you feel like you need a lot more sleep than your peers, you may find the results of a new study comforting. The study suggests that the body's internal clock programs some people to sleep longer than others, researchers report.

This internal clock, or circadian rhythm, controls when we sleep and wake and plays a role in other biological processes as well, such as temperature regulation and hormone production.

In an interview, Dr. Daniel Aeschbach explained that the body's internal clock creates a signal that divides the circadian cycle into two distinct periods--a biological day and a biological night.

During the biological night, we experience changes in hormone levels, body temperature and the propensity to sleep, explained Aeschbach, who was at the National Institute of Mental Health in Bethesda, Maryland, when the study was conducted.

"Somehow the clock programs an internal night during which it favors rest and sleep," said Aeschbach, who is now at Brigham and Women's Hospital and Harvard Medical School in Boston, Massachusetts.

Although most adults average 7.5 hours of sleep a night, some people get by on less sleep while others seem to need more z's. Researchers suspect that there is a physiological explanation for sleep differences, but exactly what this might be has been uncertain.

In the study, Aeschbach and his colleagues compared long sleepers, who usually slept more than nine hours a night, and short sleepers, who usually got less than six hours a night.

Participants were kept awake in a sleep lab for 40 hours so that both long and short sleepers would be living under the same conditions.

Based on several measures, including hormone levels, body temperature and sleepiness, long sleepers had a longer biological night than short sleepers. "This means that there are differences in internal circadian signals," Aeschbach said.

These differences, the Boston researcher noted, could help account for variations in the amount people sleep. The fact that the length of the biological night seems to vary from person to person may also help explain why it is difficult to change sleep habits willfully, he added.

What causes the differences remains unknown, however, according to the Boston researcher. Genetics and behavior are two possible explanations, he said.

The results of the study support the idea that sleep needs vary from person to person, Dr. Scott A. Rivkees of Yale University in New Haven, Connecticut, states in an editorial that accompanies the study.

Noting that "we seem to value our alarm clocks more than our internal clocks," Rivkees suggests that our society needs to find a way to accommodate each person's individual sleep requirements.