Low-dose aspirin shown to reduce risk of first stroke in women

In a long-awaited clinical trial conducted among nearly 40,000 initially healthy middle-aged American women, regular use of low-dose aspirin over a 10-year period was found to reduce the risk of stroke 17 percent. However, among the same population, researchers from Harvard-affiliated Brigham and Women’s Hospital (BWH) also found that low-dose aspirin did not benefit most women in terms of preventing first heart attacks or cardiac deaths.

“Although not widely recognized, women tend to suffer more strokes than heart attacks as compared to men, and thus these prevention data for low-dose aspirin have important public health implications,” said BWH’s Julie E. Buring, principal investigator of the Women’s Health Study (WHS). Buring is also professor of ambulatory care and prevention at Harvard Medical School (HMS).

The results of the cardiovascular component of the WHS are being presented at the American College of Cardiology (ACC) 54th Annual Scientific Session in Orlando, Fla., and were also being published simultaneously in the New England Journal of Medicine online March 7 and then in print in the March 31 issue.

The WHS is a large, randomized, double-blind, placebo-controlled trial funded by both the National Heart, Lung and Blood Institute and the National Cancer Institute to evaluate the benefits and risks of low-dose aspirin (100 mg every other day) as well as vitamin E supplementation (600 IU every other day) in the primary prevention of cardiovascular disease. The trial included 39,876 healthy women 45 years of age and older who were monitored for 10 years for first major cardiovascular events including heart attack, stroke, and death from cardiovascular causes.

With regard to aspirin, while previous trials primarily done in men have shown aspirin to be effective in lowering the risk of a first heart attack, data addressing this question in women have been limited. During follow-up, 477 major cardiovascular events were confirmed in the aspirin group as compared with 522 in the placebo group, a 9 percent overall reduction that was not statistically significant. However, in a pattern seemingly different to that previously observed among men, the benefit of aspirin within the WHS was due almost entirely to a statistically significant reduction in stroke events without a reduction in heart attack rates. The most consistent benefits were observed among women 65 years of age and older, a group that comprised 10 percent of the study population yet suffered one-third of all cardiovascular events. Among such women, low-dose aspirin use resulted in a 26 percent reduction in risk of major cardiovascular events. By contrast, low-dose aspirin showed little benefit among younger women, an important issue as aspirin use is also known to increase the risk of bleeding.

“The WHS overwhelmingly demonstrates the importance of studying medical therapies among women as well as men,” said Buring. “We finally have the evidence base needed for women to make rational decisions about the use of aspirin in preventing cardiovascular disease.”

“From a clinical standpoint, the new data suggest that many women, particularly those over the age of 65, are likely to attain a net benefit from preventive aspirin therapy,” said Paul Ridker, a BWH cardiologist also involved in the WHS clinical trial.

“However, as with men, women considering the use of aspirin to prevent cardiovascular disease must balance both benefits and risks, and thus should consult with their personal physician before beginning therapy,” added Ridker, the Eugene Braunwald Professor of Medicine at HMS.

Buring also presented data at the ACC meeting evaluating vitamin E as compared with placebo in the same group of nearly 40,000 women. Overall, women allocated to vitamin E had almost exactly the same risk of future cardiovascular events as did those allocated to placebo. “We found no evidence that dietary supplementation with vitamin E lowered risk of a first cardiovascular event,” said Buring. “With regard to vitamin E supplementation, the bottom line is that eating healthy foods and living a healthy lifestyle remain a woman’s best choice for long-term heart disease prevention.”