Chronic sleep loss can reduce the capacity of even young adults to perform basic metabolic functions such as processing and storing carbohydrates or regulating hormone secretion, according to researchers from the University of Chicago Medical Center in The Lancet.
Cutting back from the standard eight down to four hours of sleep each night produced striking changes in glucose tolerance and endocrine function—changes that resembled the effects of advanced age or the early stages of diabetes—after less than one week.
“We found that the metabolic and endocrine changes resulting from a significant sleep debt mimic many of the hallmarks of aging,” said Dr. Eve Van Cauter, professor of medicine at the University of Chicago and director of the study. “We suspect that chronic sleep loss may not only hasten the onset but could also increase the severity of age-related ailments such as diabetes, hypertension, obesity, and memory loss.”
Cutting back on sleep is an extremely common response to the time pressures of modern industrial societies. The average night’s sleep decreased from about nine hours in 1910 to about 7.5 hours in 1975, a trend that continues. Millions of shift workers average less than five hours per workday.
Previous studies have measured only the cognitive consequences of sleep loss. Dr. Van Cauter and her colleagues chose to focus instead on the physiologic effects of sleep loss: how sleep deprivation altered basic bodily functions such regulating blood-sugar levels, storing away energy from food, and the production of various hormones. They followed 11 healthy young men for 16 consecutive nights. The first three nights the subjects were allowed to sleep for eight hours, from 11 p.m. to 7 a.m. The next six nights they slept four hours, from 1 a.m. to 5 a.m. The following seven nights they spent 12 hours in bed, from 9 a.m. to 9 p.m. All subjects received identical diets.
They found profound alteration of glucose metabolism, in some situations resembling patients with type-2 diabetes, during sleep deprivation. When tested during the height of their sleep debt, subjects took 40 percent longer than the norm to regulate their blood sugar levels following a high-carbohydrate meal. Their ability to secrete insulin and to respond to insulin both decreased by about 30 percent. A similar decrease in acute insulin response is an early marker of diabetes.
Sleep deprivation also altered the production and action of other hormones, dampening the secretion of thyroid-stimulating hormone, and increasing blood levels of cortisol, especially during the afternoon and evening. Elevated evening cortisol levels are typical of much older subjects and are thought to be related to age-related health problems, such as insulin resistance and memory impairment.