Don D. Sin, MD, and colleagues at the University of British Columbia, Vancouver, Canada, looked at data from clinical trials of aspirin for the prevention of heart attack.
The evidence suggests that aspirin helps everyone who has had a heart attack. But when it came to preventing a first heart attack, different trials got different results.
Why? Studies that looked predominantly at men found that aspirin helped. Trials that looked predominantly at women found no effect.
"Our report suggests an aspirin a day reduces a man's risk of a first heart attack by 25%. In women there seems to be no effect," Sin tells WebMD. "This is true only for women with no risk factors who haven't had heart attacks in the past. People who have had heart attacks should take an aspirin a day, regardless of whether they are male or female."
Aspirin Different in Women
It's not the first study to find that aspirin has different benefits for women than it does for men. Researchers are learning that some people are resistant to aspirin's blood-thinning effects. And those people tend to be women, says Alan Heldman, MD, clinical chief of cardiology at University of Miami Miller School of Medicine.
"In several studies, the frequency of being aspirin resistant seemed to be higher among women than among men," Heldman tells WebMD. "Why would that be so? Women with heart disease are typically older than men with heart disease. That obviously has an impact on all sorts of other variables about the patient's response to treatment."
Laurence S. Sperling, MD, director of the Emory Heart Center risk reduction program, says it's not yet clear that aspirin resistance is the main reason women respond differently to aspirin than men do.
"As much as 40% of the population may have aspirin resistance. It may be that this waxes and wanes over the course of a patient's life. But there are suggestions it is more common in women," Sperling tells WebMD.
Sperling notes that the benefits of daily aspirin seem to differ between men and women.
"The data suggest aspirin offers more of a stroke-prevention effect in women rather than the heart-attack prevention effect seen in men," he says. "Still, I don't withhold aspirin as a preventive strategy in a high-risk female -- someone with diabetes, for example."
Heldman and Sin wholeheartedly agree that some women definitely benefit from preventive treatment with aspirin.
For patients with multiple risk factors for heart disease -- such as those who smoke and those with high cholesterol or diabetes -- I would probably put them on aspirin even if they haven't yet had a coronary event," Heldman says. "And I use aspirin for both men and women in that regard, although we keep our eye on the notion it may be less effective for women."
The bottom line, says Sin, is that nobody should take aspirin before talking with a doctor.
"This study is a sobering reminder to the public that before self-medicating, be sure to consult your doctor to learn whether the medicine you are about to take is right," Sin says. "And this is especially true for women and aspirin."