Even though cardiovascular disease is the leading killer of both men and women, many studies on heart disease prevention have focused on just one sex: men. That's particularly true of research on the benefits of aspirin. It's a problem because men and women metabolize medication differently, so aspirin might not protect women as well as it does men. Researchers at Boston's Brigham and Women's Hospital spent more than a decade following women who took aspirin to find out whether it helps them or not.

What the researchers wanted to know: Does aspirin reduce a women's risk of heart disease?

What they did: The researchers split nearly 40,000 healthy women, all older than 45, into two groups. Half of the group took a very low dose of aspirin (100 mg, less than a third of a Bayer aspirin tablet) every other day; the other half received a placebo pill. The researchers tracked the women for 10 years, recording problems such as heart attacks, strokes, and death from cardiac illness. They also looked for gastrointestinal bleeding, a well-known risk of taking aspirin.

What they found: In contrast to its effect on men, who seem to have fewer heart attacks when they take aspirin regularly, the drug did not reduce heart attacks or cardiac deaths in women. It did, however, reduce women's risk of the most common type of stroke—ischemic stroke, the kind caused by a blocked blood vessel in the brain—by 24 percent. Also, when the researchers looked at the aspirin-taking women by age, those over 65 did benefit; they had fewer strokes and heart attacks than women taking placebo. On the downside, for all women, gastrointestinal bleeding was more common among women who took aspirin than among the placebo group.

What it means to you: This study makes two important points. First, it shows that women, especially older women, may benefit from taking low doses of aspirin to prevent ischemic stroke. Second, because the results in this study were different from the results of studies on men, it shows that researchers need to be careful about using studies that primarily involve men to make recommendations about women's health.

Caveats: Though aspirin is available over the counter, a woman should not take it over a long period of time without first consulting her doctor. Gastrointestinal bleeding can be a serious side effect, sometimes requiring blood transfusions and surgery. So, because the researchers found that aspirin can increase the risk for this bleeding, any long-term regimen should be closely monitored.

Find out more: The Heart Truth is a federal campaign to raise awareness about women and heart disease. The website has news, information about lowering your risk for heart disease, and stories from women who have had heart disease.

The National Women's Health Information Center also has a page full of answers to women's common questions about heart disease.

Calculate your risk for heart attack and read the latest news on heart health on U.S. News's heart disease page.

Read the article: Ridker, P.M. et al. "A Randomized Trial of Low-Dose Aspirin in the Primary Prevention of Cardiovascular Disease in Women." The New England Journal of Medicine. March 31, 2005.

Abstract online: http://content.nejm.org