By Rob Stein
Washington Post Staff Writer
Monday, March 7, 2005; 10:08 AM

Aspirin does not protect women against heart attacks in the same way it does for men, but the venerable painkiller does cut women’s chances of suffering a stroke, researchers reported today.

A long-awaited 10-year study of nearly 40,000 women, the biggest and best such study to date, provides the first strong evidence of the benefits of taking aspirin regularly for healthy women, a practice that many have already begun based largely on studies of men.

The study found that aspirin does not reduce the risk of first heart attacks for middle-aged women, as it does for men, but does cut the risk of strokes, which is not the case for men. But aspirin does lower the chances of having a heart attack for older women — those age 65 and above, when the stroke-reduction benefits also appear to be the greatest.

The findings suggest that the benefits of aspirin may not outweigh the risks for healthy women in their forties and fifties, but that once they hit their sixties, the balance may shift enough to make it worthwhile. Aspirin increases the risk of bleeding, which can cause serious problems including rare but deadly bleeding strokes. Women with high blood pressure and problems with stomach bleeding may be at particular risk.

“The bottom line is that for younger women it’s not clear that there would be an overall benefit,” said Julie Buring of the Brigham and Women’s Hospital in Boston, who led the study. “But for those age 65 and older, that’s where we may see it being useful.”

The results add powerful new evidence to the growing body of data showing that men and women differ in fundamental ways on various aspects of health, and that research done on men does not necessarily translate directly to women.

“This truly underscores the importance of studying medical therapies among women as well as men,” said Buring, whose findings were released early by The New England Journal of Medicine to coincide with a presentation at an American College of Cardiology meeting in Orlando. “We can’t assume studies involving men apply to women.”

It remains unclear why women respond differently, although some have speculated that it may be due to hormonal differences or the fact that women tend to develop heart disease later in life.

“Age 50 in men is biologically about age 60 in women in terms of their risk of cardiovascular disease,” Buring said.

Aspirin, an ancient medicine known for decades mainly as a way to alleviate headaches and fevers, became a key player in the fight against cardiovascular disease — the nation’s leading killer — after doctors discovered its powers to prevent and help dissolve blood clots and reduce inflammation.

Previous research has clearly demonstrated that aspirin can help stop heart attacks as they are happening in both men and women by dissolving blood clots blocking blood flow to the heart muscle. In addition, men and women who have already had a heart attack can sharply cut their chances of having another by taking low doses of aspirin regularly.

But the value of healthy people taking low doses of aspirin on a regular basis to prevent their first heart attack has been less clear. Five studies have indicated it may have that effect, prompting aspirin makers to begin promoting that use and many men and women to start taking it. Very few women were involved in those studies, however, raising concerns many women could be needlessly exposing themselves to the drug’s risks.

“We know millions of people take aspirin thinking it will prevent them from having a heart attack,” said Scott Grundy of the University of Texas Southwestern Medical Center. “But there are risks, and there might be a huge number of women who might be taking aspirin who shouldn’t be because the risks may outweigh the benefit. We just hadn’t had the data.”

In the new, federally funded Women’s Health Study, about half of 39,876 women age 45 and older took 100 milligrams of aspirin every other day, while the other half took a placebo. After 10 years, the researchers found that aspirin did not reduce the overall risk of heart attacks. But aspirin did reduce by 17 percent the risk of strokes, which tend to strike women more than men.

When the researchers did a separate analysis of women age 65 and older, however, they found that those taking aspirin were 34 percent less likely to suffer heart attacks, and that the protection against strokes increased as well.

Other researchers said the findings represent a watershed because they finally provide women with clear evidence about the potential benefits and risks of aspirin.

“This is the definitive trial that we’ve been waiting for,” said Lori Mosca, a women’s heart expert at Columbia University.

Mosca and other experts emphasized that the potential risks of aspirin can be significant, particularly for women, making it especially crucial that they consult with their doctors to make sure any possible benefits outweigh the dangers.

“This is exactly the type of study that doctors need when they are sitting across the desk from a patient trying to decide about the best course of action,” said Larry Goldstein of Duke University, speaking for the American Heart Association.

The same study also found that vitamin E does not protect women against heart disease. That finding is the latest in a series of major blows to the theory that the vitamin, a so-called antioxidant, might provide that benefit.

© 2005 The Washington Post Company