Middle-aged and older women who typically sleep six hours or less a night, or who increase their average sleep time by two hours or more over a period of several years, have increased risk of developing type 2 diabetes, according to a new study from Harvard T.H. Chan School of Public Health.
Previous research has linked both too much and too little sleep with increased diabetes risk, with those who regularly sleep 7-8 hours a night at lowest risk. But most previous studies were smaller and measured sleep duration only once. The new study is one of the first, and the single largest, to look at long-term sleep habits — including changes over time — and how those habits affect diabetes risk. The researchers looked at nearly 60,000 U.S. women aged 55–83 between 1986 and 2000, repeatedly measuring their diet quality, physical activity, and weight, to see whether any of these factors explained the relationship of sleep duration to later risk of diabetes.
They found a link between consistently short sleep duration and type 2 diabetes, but the association had to do with body mass index and other factors. They also found that, among women who increased their sleep by two hours or more over time, diabetes risk increased by 15 percent, and that this change was not fully explained by body mass index or other factors — suggesting that, in those whose sleep duration increases over time, some other mechanism is at play involving sleep times and metabolic health. Read more