Nov. 16, 2010 -- CHICAGO -- Women who get more than 10 hours of sleep a night may increase their risk of incident stroke, researchers said here at the American Heart Association meeting.
Additionally, women who had six or less hours of sleep did not have an associated increased stroke risk, Dr. Alan Flint of the Harvard School of Public Health reported.
Flint and colleagues performed a prospective cohort study of 69,794 female nurses ages 40 to 65, measuring self-reported sleep data from 1986 to 2006 to an endpoint of fatal or nonfatal stroke.
Patients were asked to report total hours of actual sleep -- ranging from less than five to 11 or more -- as well as any confounding factors, such as alcohol intake, fruit and vegetable consumption, physical activity, and smoking status. Body mass index and the presence of diabetes or hypertension were recorded as potential intermediary factors.
At the 20-year follow-up, a total of 2,303 strokes were reported. After adjusting for confounders, Flint and colleagues found those who had slept 10 or more hours a night had a 63 percent increased risk of stroke compared with a baseline average risk with seven hours a night of sleep.
Comparatively, patients who slept six or fewer, or from eight to nine hours a night, had insignificant increases in stroke risk after adjusting for confounders, when compared with baseline.
Researchers were unable to determine any of the underlying biological mechanisms that may cause the increased risk in patients with higher sleep duration.
"We do find that identifying long sleep duration is useful in marking risk, although it doesn't immediately lead to any clinical recommendation," Flint told MedPage Today.
Future research should investigate the possible causes of the increased risk of stroke in women, he said.
"We'd like to update [the study] and get an idea of whether a pattern of sleep over a lifetime that accounts for the risk, or whether there are other factors that account for that, like clinical depression, jobs, family, or other interaction with that risk."
Flint noted he was performing similar research in a large cohort of males, though no current research existed measuring the same outcome. He added that other research indicated a bell-curve relationship for men in other cardiovascular diseases -- such as coronary heart disease -- where men were at increased risk in both lower and higher hours of sleep.