Sleeping for less than six hours or for more than nine hours each night is associated with an increased risk of Diabetes and impaired blood sugar (glucose) tolerance, researchers report in this week’s issue of the Archives of Internal Medicine.

“There are a lot of people who sleep five or six hours per night who we generally think are not getting enough sleep,” lead author Dr. Daniel J. Gottlieb told Reuters Health. His group hypothesized that people who do not get enough sleep may be at increased risk of developing diabetes or impaired glucose tolerance.

Gottlieb, of Boston University School of Medicine, and colleagues enrolled 1,486 subjects, ages 53 to 93 years, in their study. The subjects completed questionnaires regarding sleep patterns and underwent fasting glucose and glucose tolerance testing.

Diabetes was present in 20.9 percent of subjects and impaired glucose tolerance was present in another 28.2 percent. A usual sleep time of six hours or less was reported by 27.1 percent, including 8.4 percent who reported five hours or less. A total of 8.6 percent said that they slept for nine hours or more.

Compared with subjects who slept for seven to eight hours each night, the risk of diabetes was increased by 2.5-fold in those sleeping five or less hours, 1.66-fold for those sleeping six hours, and 1.79-fold for those sleeping nine or more hours. The corresponding increased risks of developing impaired glucose tolerance were 1.33-, 1.58-, and 1.88-fold. Blood glucose levels were not significantly affected by insomnia.

“These are strong associations suggesting that voluntary sleep restriction may cause impaired glucose regulation,” Gottlieb said. “Probably those sleeping nine hours or more per night are doing so because of some underlying condition that may not be diagnosed but that puts them at increased risk of diabetes,” he suggested.

The authors also noted that adequate levels of sleep should be tested as a non-drug treatment strategy in patients with Diabetes or impaired glucose tolerance.

Sleeping for at least seven hours a night, Gottlieb concluded, “is a good health practice for a variety of reasons, and this is one more reason.”

SOURCE: Archives of Internal Medicine, April 25, 2005.