People who sleep too much or not enough are at greater risk of developing type 2 diabetes or impaired glucose tolerance, say researchers at Université Laval's Faculty of Medicine.
The risk is 21/2 times higher for people who sleep less than 7 hours or more than 8 hours a night, according to the study published in journal Sleep Medicine.
To reach the conclusion, researchers analysed the life habits of 276 subjects over a 6-year period.
They determined that over the timespan, approximately 20 percent of those with long and short sleep duration developed type 2 diabetes or impaired glucose tolerance versus only 7 percent among subjects who were average duration sleepers.
Even after taking into account the effect attributable to differences in body mass among the subjects, the risk of diabetes and insulin resistance was still twice as high among those with longer and shorter sleep duration than average sleepers.
The researchers also point out that diabetes is not the only risk associated with sleep duration. A growing number of studies have shed light on a similar relationship between sleep and obesity, cardiovascular disease, and overall mortality.
The authors observe that among adults, between 7 and 8 hours of nighttime sleep appears to be the optimum duration to protect against common diseases and premature death.
However, it seems that fewer and fewer people sleep the optimum number of hours.
A survey conducted in 1960 showed that American adults slept an average of 8 to 8.9 hours a night. By 1995, that average had dropped to 7 hours. A study conducted in 2004 by the National Center for Health Statistics found that one-third of adults aged 30 to 64 slept less than 6 hours a night.