Late to bed and early to rise does more than put black circles under your eyes — it increases your risk of diabetes.

But slugabeds have no reason to celebrate. Sleeping too much also raises diabetes risk.

The findings apply to voluntary sleep time, not insomnia, report Daniel J. Gottlieb, MD, MPH, of Boston University and the VA Boston Healthcare System, and colleagues.

"Voluntary sleep restriction may contribute to the large public health burden of diabetes mellitus," they write in the April 25 issue of Archives of Internal Medicine.

The finding comes from a study of 1,500 middle-aged and elderly men and women aged 53 to 93 enrolled in a study of sleep and heart health. Study participants filled out questionnaires about their sleep habits and underwent tests for diabetes and impaired glucose tolerance, an early diabetes symptom.

After ruling out possible effects of obesity, sleep apnea, sex, age, and race, the researchers found a strong link between diabetes, impaired glucose tolerance, and too little sleep.

The findings:

— Diabetes was 2.5 times more common in those who slept five hours or less per night.

— Diabetes was 66 percent more common in those who slept six hours a night.

— Diabetes was 79 percent more common in those who slept nine or more hours per night.

"The association of short sleep times with [diabetes] and impaired glucose tolerance may explain in part the association between short sleep time and [heart attack] and mortality," Gottlieb and colleagues write.

The findings, they suggest, support doctors' longstanding advice to get seven to eight hours of sleep each night.

The researchers also suggest that it might be helpful for people with diabetes — or those at risk of diabetes — to get enough sleep.

It's not clear why sleeping too much is also linked to diabetes. Gottlieb and colleagues speculate that alcohol use may be involved.

By Daniel J. DeNoon, reviewed by Brunilda Nazario, MD

SOURCE: Gottlieb, D. Archives of Internal Medicine, April 25, 2005; vol 165: pp 836-868.