Getting enough sleep — but not too much — may be a safeguard against type 2 diabetes, new research in the journal Sleep Medicine shows.

People who slept less than six hours a night were more than twice as likely as people who got seven to eight hours to develop diabetes or impaired glucose tolerance (IGT), as were those who reported getting nine or more hours of sleep a night, Dr. Jean-Philippe Chaput of Laval University in Quebec City and his colleagues found.

"These results suggest that sleep duration may represent a novel risk factor for type 2 diabetes/IGT," they conclude.

Evidence linking long-term sleep deprivation to diabetes is mounting, Chaput and his team point out. To further in investigate, for an average of six years they followed 276 people 21 to 64 years old, all of whom initially had normal glucose metabolism at study enrollment.

After adjusting for several factors that could affect both sleep duration and diabetes risk, such as physical activity level, age and smoking habits, Chaput and his colleagues found that people who got six hours of sleep or less a night were 2.78 times more likely to develop IGT or full-fledged type 2 diabetes during the course of the study, while risk was 2.54 times greater for people sleeping nine hours or more.

When the researchers adjusted the data to factor out the influence of excess body weight indications, such as waist circumference, percentage body fat, and body mass index, the link was weakened somewhat, suggesting that obesity was a factor in the relationship as well.

Chronically short sleep can cause "striking" changes in metabolism and hormone secretion, the researchers note, which could put these people at risk of type 2 diabetes. People who sleep too much, on the other hand, may have underlying conditions such as sleep-disordered breathing that might influence diabetes risk, they add; there's also some evidence that people who sleep more are less active.

No matter what the mechanism might be, the researchers say, the findings provide more evidence that "the practice of good sleep hygiene is crucial and should be included with other behaviors to achieve good health."