Sleep patterns in middle-aged women can increase their risk for stroke, researchers in the United States have found. The greatest increase in stroke risk - 70 percent - was noted among women who slept 9 hours or more per night, according to their report in the medical journal Stroke.

A link between sleep duration and mortality has previously been noted in a number of studies, but evidence of an association between sleep patterns and cardiovascular disease has been lacking, Dr. Jiu-Chiuan Chen, from the University of North Carolina in Chapel Hill, and co-researchers note.

The current investigation included 93,175 women, between 50 and 79 years of age, who were enrolled in the Women’s Health Initiative study.

Overall, 8.3 percent of these women reported than they normally slept no more than 5 hours per night, while 4.6 percent reported sleeping at least 9 hours per night.

After following the group for an average of 7.5 years, the researchers found that 1,166 women experienced an ischemic stroke, the most common type of stroke, which occurs when a blood vessel in the brain becomes blocked. This prevents oxygen from reaching the brain and the brain’s tissue begins to die.

Upon further analysis, Chen’s group found that women with a sleep duration of 6 hours or less, 8 hours, or 9 hours or more increased the risk of stroke by 14 percent, 24 percent, and 70 percent, respectively, compared with sleeping 7 hours.

The adverse effect of sleeping 6 hours or less was more pronounced in women who had cardiovascular disease at beginning of the study. In these subjects, this amount of sleep increased their risk of stroke by 22 percent.

Further analysis also suggested that the adverse effect of long periods of sleep was not associated with frequent snoring or sleepiness. Therefore, sleep patterns that are longer or shorter than the norm could be independent risk factors for stroke, the authors comment.

“The prevalence in women of having long sleep duration is much lower than having sleep duration less than 6 hours. So the overall public health impact of short sleep is probably longer than long sleep,” Chen explained a statement.

Chen added: “Our data do not imply that if women with long sleep cut their sleep hours they would be at a lower risk….Further studies are needed to help us understand the possible mechanisms involved in the associations found in this study.”

SOURCE: Stroke, July 27, 2008 rapid access.