Sleeping more or less than 7-8 hours a night was associated with a significantly greater risk of developing type 2 diabetes or impaired glucose tolerance, in a 6-year study of 276 adults.
The results “concur with a growing body of epidemiological evidence showing a U-shaped relationship between sleep duration and body weight, type 2 diabetes, coronary heart disease, and all-cause mortality,” wrote Dr. Jean-Philippe Chaput of Laval University, Quebec City, and his associates. The study is in press at Sleep Medicine (doi:10.1016/j.sleep.2008.09.016
Among the 276 men and women (aged 21-64) in the current cohort study, 21% who slept an average of 6 hours or less a night and 19% of those who slept an average of 9 hours or more a night developed type 2 diabetes or impaired glucose tolerance (IGT) over a mean of 6 years, compared with 7% of those who slept an average of 7-8 hours a night.
After adjustment for confounding factors associated with sleep duration and/or type 2 diabetes/IGT, such as age, smoking habits, shift work, and vigorous physical activity, those who slept 6 hours or less a night had a 2.78 times greater risk of developing diabetes and those who slept 9 or more hours a night had a 2.54 times greater risk, compared with those who slept 7-8 hours; the differences were significant.
After adjustment for waist circumference, the increased relative risk for the groups who slept more or less than 7-8 hours remained significant. There were no sex differences in risk.
Previous data have suggested that prolonged partial sleep deprivation could predispose people to abnormal metabolic regulation, including clinical diabetes, and that partial sleep restriction can cause changes in metabolic and endocrine functions, such as insulin resistance and reduced carbohydrate tolerance.
The mechanism underlying the impact of too much sleep is more speculative, they wrote. One possible explanation is that sleep disorders associated with more sleep, such as sleep-disordered breathing, are also associated with obesity, insulin resistance, and diabetes.
The subjects in the study were part of the Quebec Family Study, a study on the influence of genetics on the etiology of obesity, fitness, and cardiovascular and diabetes risk factors, in 1,650 people from 375 families.