Contact: Eve Van Cauter, PhD
(773) 702-0169
evcauter@medicine.bsd.uchicago.edu

Sleep Debt Affects Metabolic Functions

Chronic sleep loss can have a detrimental effect on metabolic functions, new research shows.

"The state of sleep debt has a harmful impact on carbohydrate metabolism and endocrine function," write Karine Spiegel, PhD, and colleagues in the October 23, 1999 issue of The Lancet, a leading British medical journal. These effects are commonly seen as part of the normal aging process, and persistent sleep debt may, therefore, increase the severity of age-related chronic disorders.

During this century, the average number of hours that people spend asleep per night in more-developed countries has decreased from nine hours to 7.5 hours. The change has been made to accommodate increased demands of work, with around-the-clock production, shift work, etc, as well as more leisure activities. The consensus is that sleep is beneficial for the brain but not for the rest of the body. There have been reports that the number of hours asleep each night can be voluntarily decreased without affecting daytime sleepiness, mood, or cognitive function.

The scientists at the Department of Medicine, University of Chicago, investigated whether sleep debt can alter metabolic and hormonal functions. Eleven young men were enrolled into the study, and their carbohydrate metabolism and hormonal functions were studied. For the first three nights, the men were in bed for eight hours (fully rested condition). For six nights they were in bed for four hours per night (sleep-debt condition), and for the last seven nights they were in bed for 12 hours per night. The investigators took measurements during the day of glucose tolerance, cortisol concentrations (a hormone that helps to regulate blood sugar concentrations), heart rate, sleepiness, and the profiles of hormones of the hypothalamus, and the pituitary and adrenal glands.

At the end of the sleep-debt conditions, glucose concentrations in the blood were higher than in the fully rested conditions, and concentrations of thyrotropin, which regulates the release of thyroid hormones, were lower. Cortisol concentrations in the evening were increased after sleep debt, as was the activity of the sympathetic nervous system, which controls many of the body's "involuntary" functions.

The research was supported by a grant from the Research Network on Mind-Body Interactions of the MacArthur Foundation, by a grant from the U.S. Air Force Office of Scientific Research, and by grants from the National Institutes of Health.

###