Deep sleep, also called “slow-wave sleep,” is thought to be the most restorative sleep stage, but its significance for physical well-being has not been demonstrated. A new study conducted by researchers at the University of Chicago Medical Center shows that loss of slow-wave sleep in healthy young adults significantly increases their risk of type 2 diabetes by impairing their ability to regulate blood-sugar levels.

Previous studies have demonstrated that reduced sleep quantity can impair glucose metabolism and appetite regulation, resulting in increased risk of obesity and diabetes. This current study provides the first evidence linking poor sleep quality to increased diabetes risk.

The researchers studied nine lean, healthy volunteers, five men and four women between the ages of 20 and 31. The subjects spent two consecutive nights in the sleep laboratory, where they were monitored while they slept undisturbed.

The same subjects were next studied for three consecutive nights during which their sleep was disturbed by sounds administered through speakers whenever they showed signs of entering into slow-wave sleep.

This study found that after only three nights of interrupted slow-wave sleep, young healthy subjects became less sensitive to insulin, resulting in reduced tolerance to glucose and increased risk for type 2 diabetes. The decrease in insulin sensitivity was comparable to that caused by gaining 20 to 30 pounds.

“This decrease in slow-wave sleep resembles the changes in sleep patterns caused by 40 years of aging,” said Esra Tasali, MD, assistant professor of medicine at the University of Chicago Medical Center. Young adults typically spend 80 to 100 minutes per night in slow-wave sleep, while people over age 60 generally have less than 20 minutes. “In this experiment, we gave people in their 20s the sleep of those in their 60s.”

The alarming rise in the prevalence of type 2 diabetes is generally attributed to the epidemic of obesity combined with the aging of the population. “Previous studies from our lab have demonstrated many connections between chronic, partial, sleep deprivation, changes in appetite, metabolic abnormalities, obesity, and diabetes risk,” said Van Cauter. “These results solidify those links and add a new wrinkle, the role of poor sleep quality, which is also associated with aging.”

“Chronic shallow non-REM sleep, decreased insulin sensitivity and elevated diabetes risk are typical of aging,” the authors conclude. “Our findings raise the question of whether age-related changes in sleep quality contribute to the development of these metabolic alterations.