Lack of sleep increases insulin resistance

Add another item to your list of reasons patients (and you) should get adequate sleep: Sleep deprivation escalates insulin resistance. University of Chicago sleep researchers presented a paper to delegates to the Alexandria, VA-based American Diabetes Association’s annual scientific sessions in June showing results of an as yet unpublished study showing inadequate sleep may prompt the development of insulin resistance and increase the risk of developing diabetes.

"We have shown that failure to get slightly more than eight hours of sleep per night may contribute to the rising incidence of diabetes," says Bryce Mander, a research assistant in the endocrinology section of the University of Chicago Medical School. "What this shows is that when you chronically get inadequate sleep, you are not merely developing a sleep debt but also disrupting other body functions. That is roughly equivalent to the disruption caused by the process of aging," explains Mander, who is chief assistant to renowned sleep researcher Eve Van Cauter, PhD, professor of medicine at the University of Chicago.

The study included 27 healthy, nonobese adults ages 23-42 years, 14 of whom were considered "normal sleepers" (with an average sleep duration of 7.5-8.5 hours) and compared them with 13 who were chronic "short sleepers" (with an average weekday sleep duration of less than 6.5 hours). Their sleep patterns had been stable for at least six months. The two groups were matched for gender and ethnic distributions, exercise habits, and diabetic family history.

Participants wore a wrist activity monitor for eight consecutive nights, and on the last two, recorded their sleep at home using an ambulatory recording system. Over the course of the study, the short sleepers averaged five hours and 16 minutes per night, while the long sleepers averaged seven hours and 57 minutes per night. Final analysis of glucose tolerance tests taken at the end of the eight days showed that insulin sensitivity diminished by nearly 40% in the short sleepers, indicating that "chronic sleep curtailment in otherwise healthy young adults impairs the ability of insulin to do its job properly."

So the list of risk factors for insulin resistance gets longer: poor diet, sedentary lifestyle, chronic stress, aging — and now sleep deprivation.

The National Sleep Foundation in Washington, DC, says the average American gets 6.5 hours of sleep a night — about 20% less than they need. Those who get less than 6 hours of sleep a night lose judgment and coordination roughly on a par with those who have a blood alcohol content of 0.05%, which approaches the legal limit for drunk driving in many places. The organization also documents a steady decline in the number of hours Americans sleep each night. In 1975, the average American slept 7.5 hours, down from 9 hours in 1910.

Cutting back on sleep is a common response to the time pressures of modern industrial societies, Mander noted, and in our increasingly hectic modern lifestyle, sleep often is sacrificed in favor of work, family life, and social activities.

"All of this makes sense to me, and it certainly merits more research," says Bruce Bower, MD, FACE, an endocrinologist in Hartford, CT. Bowers notes the diurnal rise in cortisol from the adrenals and growth hormone from the pituitary are counter-regulatory hormones that oppose the action of insulin, resulting in rising blood sugar. "Relative insulin resistance occurs at the time when these hormones are at their peaks, which could explain increased insulin resistance in people who are sleep-deprived," says Bower.

Mander agrees that production of the stress hormone cortisol is "probably related," but his team did not specifically study this aspect of insulin resistance. "Short sleep is a general stressor on all related body functions," Mander adds.

An earlier study from the University of Chicago demonstrated that 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.1 In 1999, Van Cauter’s research showed that subjects who received only four hours of sleep a night quickly produced striking changes that resembled the effects of aging or early diabetes.

"We found that metabolic and endocrine changes resulting from significant sleep debt mimic many of the hallmarks of aging," said Van Cauter at the time the study was published. "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."

A year ago, Van Cauter published a paper reporting two stages of age-related deterioration of sleep quality, the first in young adulthood between the ages of 16 and 25 and the other at midlife between the ages of 35 and 50. Those changes in sleep patterns were mirrored by changes in hormone secretion.

Although total sleep remained constant as young adults moved into midlife, the proportion of slow-wave or deep sleep decreased from nearly 20% of a normal night’s sleep for those younger than 25 years to less than 5% for those older than 35 years. Growth hormone secretion, which occurs primarily during deep sleep, also declined by 75%. Among the findings of that paper, by the age of 45 years, most men have almost entirely lost the ability to generate significant amounts of deep sleep, suggesting that most middle-aged men have very low levels of growth hormone.

The "take home" for health care professionals? "Tell your patients that sleep is necessary for health and for the healing process," says Mander. As an additional recommendation, Mander says health care professionals working with insulin-resistant patients and patients diagnosed with diabetes might consider adding increased sleep for patients for whom diet and exercise are not effectively lowering blood sugars. "That one small behavioral difference might help them improve blood sugar control," he says.

"While this most recent study is hardly a lynchpin to demonstrate the connection (between sleep and insulin resistance), it’s hard to argue with a recommendation to get a good night’s sleep — and longer sleep periods are desirable for most people," concludes Bower.

Reference

1. Spiegel K, et al. Impact of sleep debt on metabolic and endocrine function. Lancet 1991; 354:1,435-1,439.