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Being overweight has long been associated with a higher risk of stroke for women. However, a recent analysis of a large observational study indicates that the correlation holds only for strokes caused by blood clots (the most common kind). In fact, heavier women actually have a lower risk of bleeding strokes compared with their lighter counterparts.
Researchers from the University of Oxford analyzed data from the Million Women Study in the United Kingdom, which followed 1.3 million women with an average age of 57 for 12 years. During that period, 20,549 suffered a stroke. Of those strokes, 9,993 were ischemic (caused by blood clots), 5,852 were hemorrhagic (caused by bleeding), and 4,704 were unspecified.
The researchers calculated that for every five-point increase in body mass index (BMI), risk of ischemic stroke rose by 21%. In contrast, that same amount of BMI increase was associated with a 12% drop in risk of hemorrhagic stroke.
Researchers continue to search for characteristics—such as levels of blood fats—that may explain the difference. However, ischemic stokes far outnumber hemorrhagic strokes, so having a higher BMI is still associated with an increased total stroke risk. The analysis was published online Sept. 7, 2016, by Neurology.