New York: Excess sleep may be a more serious sign of stroke risk among postmenopausal women than not getting enough sleep, according to a study by US researchers.

Postmenopausal women who slept nine or more hours per night were 70 percent more likely to suffer an ischemic stroke than women who slept an average of seven hours a night, according to the study published in Stroke: Journal of the American Heart Association.

An ischemic stroke is the most common type of stroke and is caused by a blockage in an artery supplying blood to the brain.

In comparison, women who slept six hours or less per night had a 14 percent higher risk of stroke compared to those who slept seven hours a night.

"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," said Sylvia Wassertheil-Smoller of the Albert Einstein College of Medicine in a statement.

The study compared sleeping patterns and stroke risk among 93,175 women aged 50 to 79 years, WebMD reported.

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, socio-economic and lifestyle factors, and depression symptoms.

In this study, researchers accounted for known stroke risk factors in analysing the link between sleep and stroke risk.

"This study provides additional evidence that habitual sleep patterns in postmenopausal women could be important for determining the risk of ischemic stroke," said Jiu-Chiuan Chen, assistant professor of epidemiology at the University of North Carolina's School of Public Health. IANS