Researchers found that postmenopausal women who slept nine or more hours per night were 70% more likely to suffer an ischemic stroke than women who slept an average of seven hours a night.
In comparison, women who slept six hours or less per night had a 14% higher risk of stroke compared to those who slept seven hours a night.
"What we don't know is whether the longer sleep time was the reason for the increased risk or whether there was some other factor that both led people to sleep more and was also a risk factor for stroke," researcher Sylvia Wassertheil-Smoller, PhD of the Albert Einstein College of Medicine in New York City says in a news release.
"In other words, this study does not mean that if you cut your hours of sleep you would lower your stroke risk. It does mean that people who sleep excessively long hours habitually (or who sleep less than six hours habitually), should discuss this with their doctors and be sure to lower their other risk factors for stroke, especially high blood pressure."
Sleep and Stroke Risk
In the study, published in Stroke: Journal of the American Heart Association, researchers compared sleeping patterns and stroke risk among 93,175 women aged 50 to 79 years.
Although previous studies have provided mixed results on the link between sleep and stroke risk, researchers say some didn't account for other factors that may affect the risk of stroke, such as race, socioeconomic and lifestyle factors, and depression symptoms.
In this study, researchers accounted for known stroke risk factors in analyzing the link between sleep and stroke risk and found an increased risk among those who slept more or less than seven hours per night.
There were 1,166 cases of ischemic stroke over the course of the study (average follow-up of 7.5 years). The lowest risk for stroke was seen in women who slept seven hours a night. The results showed that compared to women sleeping seven hours a night, women who slept nine hours or more had a 70% higher risk of stroke. Those who slept less than six hours per night had a 14% higher risk of stroke. These findings took into account age, race, socioeconomic status, depression, smoking, exercise, use of hormone therapy, and cardiovascular risk factors such as past history or stroke or heart attack, high blood pressure, and diabetes.
Although the degree of increased risk associated with getting too much sleep was much higher than that associated with getting too little sleep, researchers say nearly twice as many women reported getting less than six hours of sleep a night (8.3%) compared with those who got nine hours or more (4.6%).
"The prevalence in women of having long sleep duration is much lower than having sleep duration less than six hours. So the overall public health impact of short sleep is probably larger than long sleep," researcher Jiu-Chiuan Chen, MD, ScD., assistant professor of epidemiology at the University of North Carolina's School of Public Health in Chapel Hill, says in a news release. "This study provides additional evidence that habitual sleep patterns in postmenopausal women could be important for determining the risk of ischemic stroke."
Chen is careful to point out that these results apply only to postmenopausal women and can't be applied to other groups.