Issue 121 Item 3 Missed ZZZ’s, More Diabetes?

One-third of the population sleeps 6.5 or fewer hours, far less than the 8 hours that many sleep specialists recommend, which can impair the body’s processing of glucose. People in the United States sleep an average of 7.0 hours on weeknights, 1.5 hour less than they did a century ago, according to the National Sleep Foundation in Washington, D.C.

Several recent studies report that reducing sleep to 6.5 or fewer hours for successive nights causes potentially harmful metabolic, hormonal, and immune changes, at least in test volunteers in the sleep lab.

It’s still too early for doctors to start prescribing sleep to ward off age-related disease. Scientists agree that the findings are preliminary and that larger experiments are needed. If the story bears out, however, U.S. sleep habits may be having enormous public health consequences.

Van Cauter and her colleagues helped launch the field with a surprising 1999 study that showed that sleep deficits of several hours a night can impair the body’s processing of the sugar glucose.

The study reported that 11 healthy, lean young men showed signs of insulin resistance after several nights of sleep restriction. Insulin resistance, a condition in which the body handles glucose poorly because cells respond inefficiently to insulin, is a precursor to type II diabetes.

Experimenters carefully controlled the men’s sleep time, food intake, and exercise during their 2-week stay in the sleep lab. During the sleep-restriction phase of the experiment, the men were kept awake by minimally stressful activities, such as watching television, joking with the staff, and playing games, Van Cauter says.

The restraints imposed in the study, which permitted only 4 hours of sleep a night for 6 nights, were more severe than most people in the United States experience. The study also excluded women. So, the scientists next compared 13 men and women who habitually slept 6.5 hours or less per night at home with 14 men and women who regularly slept about 8 hours. On the weekends, the short sleepers slept extra hours, indicating that their weekday patterns resulted from social constraints rather than biological constitution, Van Cauter notes.

Researchers verified the test volunteers’ sleep patterns at home for a week and then brought them into the lab for a glucose-tolerance test. The short sleepers showed 50 percent more insulin resistance than the others did (SN: 7/14/01, p. 31: Available to subscribers at https://www.sciencenews.org/20010714/note13.asp.).

Short sleep may accelerate the onset of diabetes, Van Cauter speculates. "If you are predisposed to diabetes, and you might become diabetic at 55, are you becoming diabetic at 45?" she asks.

Modest sleep deprivation may also be associated with low-grade inflammation, which can lead to a host of cardiovascular problems, according to Alexandros N. Vgontzas of the Pennsylvania State University College of Medicine in Hershey.

A recent epidemiological study also showed a direct association between short sleep and heart disease. After controlling for other factors, researchers found that men who slept 5 hours or less a night had twice as many heart attacks as men who slept 8 hours, report Japanese scientists in the July Occupational and Environmental Medicine.

Research on sleep deprivation and health is still in its infancy, Van Cauter admits. Nevertheless, she maintains that 8 or more hours of sleep a night is optimal.

Spiegel, K. and E. Van Cauter. 1999. Impact of sleep debt on metabolic and endocrine function. Lancet 255(Oct. 23):1435-1439. Van Cauter, E., et al. 2001. Impact of sleep length on the 24-hour leptin profile. Meeting of the Association of Professional Sleep Societies. June. Chicago.Vgontzas, A.N. 2002. Modest sleep loss increases/alters normal secretion of IL-6, TNF-alpha, cortisol. 84th Annual Meeting of the Endocrine Society. June. San Francisco.