Stroke is not an equal-opportunity health issue. Even accounting for women’s average longer life spans, more women than men in the US die of stroke—it’s the fourth-leading cause of death for women but only the fifth for men. And women with diabetes and abnormal heart rhythms are more likely to have strokes than men with these conditions. While doctors have long known these facts, their cause has not been clear. Now new research sheds light on what could be driving women’s increased stroke risk.

Recent finding: Researchers at Brigham and Women’s Hospital in Boston reviewed the scientific literature on ischemic stroke (when blood flow through an artery in the brain is blocked) looking for clues as to why women are more prone to stroke than men. They evaluated the data according to factors specific to women such as sex hormones, pregnancy and menopause.

Results: As expected, the researchers found that the most common causes of stroke for both men and women were conditions such as smoking, high blood pressure, diabetes and abnormal heart rhythms. However, they also found specific hormone-based risk factors unique to women that could be contributing to their higher stroke rates. Some of these factors are already known to raise stroke risk—early menopause (before age 45)…use of  oral contraceptive pills that contained synthetic estrogen…being pregnant…and taking oral synthetic estrogen hormone therapy for menopausal symptoms. However, researchers also found two unsuspected factors associated with stroke—having begun to have monthly periods early (before age 10)…and having a low level of DHEA-S, a naturally occurring hormone that is a building block of testosterone and estrogen and that decreases with age and stress.

Bottom line: The researchers point out that more studies are needed to find out exactly how these hormonal characteristics might increase stroke risk and the best way to address the risk. However, while not much can be done about some risk factors, such as when periods begin or menopause starts, knowing more about unique risks they face reinforces for women—now maybe more than ever—why it’s good to take charge of what is within their control. According to the American Heart Association and the American Stroke Association, 80% of strokes are preventable, and recommendations for everyone (women and men) to reduce their stroke risk include maintaining healthy blood pressure, blood sugar, weight and cholesterol, eating a healthy diet that includes at least five daily servings of fruits and vegetables, getting adequate exercise, limiting alcohol and not smoking.