Low doses of aspirin can reduce stroke risk among healthy, middle-age women, according to a study released yesterday that for the first time takes a large-scale look at ways to prevent cardiovascular problems in women rather than men.
"The study is very significant," said Dr. Elizabeth G. Nabel, director of the National Heart, Lung and Blood Institute (NHLBI), which is part of the National Institutes of Health. "It has major public health implications."
The Women's Health Study found that aspirin seems to have different benefits for men and women. Several trials have found that in men, aspirin reduces the risk of heart attack, but not stroke. By contrast, the new study found that in women overall, aspirin had no effect on heart attack but lowered the stroke hazard.
For older women, aspirin showed a wider benefit: In those 65 and older, it reduced by 26 percent the risk of cardiac events, including heart attack and stroke.
The results were published online yesterday by The New England Journal of Medicine and released at the annual meeting of the American College of Cardiology in Orlando, Fla.
The study, which lasted 10 years, followed almost 40,000 women across the country.
All subjects were 45 and older and worked as health professionals, including nurses, doctors and veterinarians. Half took 100 milligrams of aspirin - slightly more than a "baby" dose - every other day. The other half took a placebo. The study, which cost $30 million, was funded by the NHLBI and the National Cancer Institute.
Researchers found a 17 percent reduction in stroke risk for the aspirin group. There was a 9 percent drop in heart attack for the aspirin takers, but researchers said this was not statistically significant.
"This study showed there is no benefit for heart attack, only for stroke," said Julie Buring, Harvard Medical School epidemiologist, one of the study's lead authors, referring to women overall.
The study also looked at vitamin E for its potential cardiovascular benefits and found it had no effect. Those results corroborate a study published last fall by researchers at the Johns Hopkins University, which found that vitamin E has no benefit might actually cause harm at higher doses.
Buring said she was surprised by the vitamin E results. "We went in expecting a benefit, but that's not what we found," she said. The study is also examining whether aspirin or vitamin E can reduce cancer risk. Those results will be released in a few months, Buring said.
Researchers and doctors have long known that low-dose aspirin could help prevent heart attacks in both men and women who had suffered a previous attack. And researchers had shown that aspirin could also reduce cardiovascular risks for healthy men.
But there was little research on aspirin's effects on healthy women. Of five major studies of aspirin's effects on healthy people, three had focused solely on men, while the other two included far fewer women than men.
Until recently, researchers and doctors paid little attention to women's cardiovascular risks.
"For many years, we were taught that heart disease was a man's disease," said Nabel.
Women make up slightly less than half of the 13 million Americans with heart disease. Every year, 345,000 women have a heart attack, and almost 400,000 have a stroke.
However, Nabel and others warned that taking low-dose aspirin carries a risk of gastrointestinal bleeding. In the aspirin group, 127 women needed blood transfusions after such bleeding, compared with 91 in the placebo group. "It's important to weigh the risks and benefits," she said.
It is not clear why aspirin appears to have differing effects on men and women.
Buring noted that the previous studies focusing on men had used a larger dose of aspirin than the new study on women. At a higher dose, aspirin might reduce women's heart attack rate, too, she said. Others suspect that the difference is based on some physical disparity.
"I think there are biological differences in response to aspirin," said Dr. Marlene Williams, a cardiologist and an assistant professor at the Johns Hopkins University School of Medicine.
Aspirin might be metabolized differently in women and men because of genetic differences, she said.
Another reason for the disparity, Williams said, is that women tend not to have heart attacks until after menopause. So the full benefits of aspirin might not show up until after age 60, when women's cardiovascular vulnerability rises. "Past menopause, that's when women start having more heart attacks," she said.
Williams said that the study will save lives, by helping women and doctors better understand who should take aspirin for prevention. Although some women take aspirin for cardiovascular benefit, the study might increase the practice. Women older than 65 and those who have a high risk of stroke are the most likely candidates, based on the study results, she said.
