Aspirin Does Not Prevent Heart Attacks in Women, Study Finds

By MARY DUENWALD

Published: March 8, 2005

Regular use of low-dose aspirin does not prevent first heart attacks in women younger than 65, as it does in men, a 10-year study of healthy women has found.

The participants in the Women's Health Study who took 100 milligrams of aspirin every other day were no less likely to suffer heart attacks than the participants in another group who took placebos. Each group had about 20,000 members.

But aspirin did appear to help protect the women against one kind of stroke - something the drug has not been found conclusively to do for men.

"What was really surprising and not anticipated was this gender difference," said Dr. Elizabeth G. Nabel, director of the National Heart, Lung and Blood Institute, which helped finance the Women's Health Study.

The study of healthy women over 45, conducted by researchers at Brigham and Women's Hospital in Boston, was the first large clinical trial to look specifically at the effects of aspirin on women.

Earlier aspirin studies had been focused entirely or largely on men. Studies in men have indicated that aspirin protects them against heart attacks. In 1989, for example, the Physicians' Health Study of healthy men from 40 to 84 found that those who took 325 milligrams of aspirin (the amount in a standard pill) every other day received a 44 percent reduction in their risk of heart attack.

Subsequent studies using smaller doses of aspirin showed a similar benefit in men.

In the current study, among women who took aspirin, the risk of all "cardiovascular events" together - including heart attacks, strokes and death from cardiovascular problems - was 9 percent lower than it was for the placebo group. That difference was not significant, the researchers said.

Because aspirin carries a risk of bleeding, doctors do not currently advise healthy women or healthy men with no clear risk of heart disease to take aspirin to prevent heart attacks or strokes. The study results are unlikely to change that practice.

Women whose risk is higher because they are over 65, have high blood pressure, are diabetic or have a family history of cardiovascular problems, for example, are often advised to take a baby aspirin daily. That practice is also unlikely to change.

The study results may help doctors fine-tune the way they measure cardiovascular risk, taking into account that women below 65 may be more vulnerable to stroke.

The message here is that women need to know their individual risk, said Dr. Sidney C. Smith, director of the center for cardiovascular medicine at the University of North Carolina, who helped write the American Heart Associations guidelines for preventing heart disease in women.

The results were presented yesterday at the American College of Cardiology meeting in Orlando, Fla., and they will be published in the March 31 issue of The New England Journal of Medicine.

The women taking aspirin had about the same number of heart attacks as the participants taking a placebo.

But the number of strokes in the aspirin group was 17 percent lower. And the aspirin takers had an especially low risk of ischemic stroke, the most common kind, caused by a blood clot in an artery leading to the brain - 24 percent lower than the placebo group.

The risk of hemorrhagic stroke, the kind caused by bleeding, was slightly higher in the aspirin group, as expected, because aspirin reduces the blood's tendency to clot.

"The fact that there was a benefit on stroke is very important for women," said Dr. Julie E. Buring, the principal investigator, "because we had many more strokes in our study than we had heart attacks."

Over the 10 years that the study was conducted, the subjects had a total of 391 heart attacks and 487 strokes.

The greater number of strokes points up what may be an important difference between men and women.

It may explain why heart disease is often considered less of a problem for women than for men - even though more women than men die of it each year, Dr. Nabel said.

"Perhaps in the past cardiologists have focused a lot on the heart and heart attacks and haven't focused sufficiently on strokes," Dr. Nabel said.

"Perhaps this will lead cardiologists, neurologists, internists and family practitioners to think more broadly about how cardiovascular disease really affects the heart and the brain," she added.

Given that both strokes and heart attacks are caused by blood clots in the arteries, it is not immediately clear why aspirin are protective only against strokes in women.

The explanation may have something to do with the size of the blood vessels that lead to the brain, which are somewhat smaller than those that lead to the heart, Dr. Buring said.