If you do not get enough slow-wave sleep your ability to regulate blood-sugar levels is significantly undermined, and your risk of developing type 2 diabetes is substantially increased, according to an article published in the Proceedings of the National Academy of Science.

The authors, from the University of Chicago Medical Center, explain that slow-wave sleep, or deep sleep, is known as the most restorative sleep stage. However, studies have not demonstrated how significant it is for physical well-being.

In this study the scientists found that young healthy adults who had their slow-wave sleep suppressed just for three nights became less sensitive to insulin. Even though their bodies needed additional insulin to dispose of the same quantity of glucose, they did not secrete the additional insulin to make up for the lower sensitivity. This resulted in reduced tolerance to glucose and a raised risk for diabetes type 2. Their lower insulin sensitivity after three nights of suppressed slow-wave sleep was equivalent to gaining 20 to 30 pounds in bodyweight.

Although other studies had shown that sleep problems could impair glucose metabolism and appetite regulation which could result in a higher risk of diabetes and obesity, this study is the first to have evidence linking lack of sleep to increased diabetes risk.

Lead author, Esra Tasali, MD, Assistant Professor of Medicine, University of Chicago Medical Center, said “These findings demonstrate a clear role for slow-wave sleep in maintaining normal glucose control,” “A profound decrease in slow-wave sleep had an immediate and significant adverse effect on insulin sensitivity and glucose tolerance.”

Eve Van Cauter, PhD, Professor of Medicine, University of Chicago, and senior author of the study, said “Since reduced amounts of deep sleep are typical of aging and of common obesity-related sleep disorders, such as obstructive sleep apnea these results suggest that strategies to improve sleep quality, as well as quantity, may help to prevent or delay the onset of type 2 diabetes in populations at risk,”

This study involved five men and four women; they were all lean, healthy, and aged 20-31. They spent two consecutive nights in a sleep laboratory. They went to bed at 11pm and got up at 7.30am the next morning. They were carefully monitored but were not disturbed.

Then they were studied for three consecutive nights. During these nights their sleep was disturbed with sounds that were administered through speakers next to their beds. This happened each time their brains indicated that they were drifting into slow-wave sleep. The sounds were not enough to wake them up, but enough to disrupt their deep sleep. The scientists managed to lower their slow-wave sleep by approximately 90%. The participants did not sleep fewer hours, but they shifted from the onset of deep sleep (stage 3 or 4) to a stage 2 sleep (lighter sleep).

“Our system proved quite effective,” Tasali said. When the participants were asked next morning they remembered hearing a noise three or four times during the night – some said they heard the noise 10 to 15 times. On average, however, subjects required about 250-300 interventions each night, fewer the first night but more on subsequent nights as “slow-wave pressure,” the body’s need for deep sleep, accumulated night after night.

Tasali added “This decrease in slow-wave sleep resembles the changes in sleep patterns caused by 40 years of aging.” An elderly person spends less than 20 minutes each night in slow-wave sleep, compared to 80-100 minutes for a young adult. In other words, the young had the same quality sleep experienced by people over 60.

During each study the scientists gave intravenous glucose (a sugar solution) to each participant, and then took regular blood samples measure the levels of glucose and insulin, the hormone that controls glucose uptake.

They found that the young adults became about 25% less sensitive to insulin after three nights of suppressed slow-wave sleep. As their insulin sensitivity fell, they required more insulin to get rid of the same amount of glucose. However, eight of the nine participants did not secrete the extra insulin needed to make up for the reduced effects. This resulted in a 23% increased in blood-glucose levels – similar to that of older adults with impaired glucose tolerance.

The young adults with low baseline levels of slow-wave sleep had the lowest levels after having their sleep patterns disrupted and the greatest decrease in insulin sensitivity.

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

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

This study was funded by the National Institutes of Health (NIH).

University of Chicago Medical Center