Aspirin prevents cardiovascular events in both women and men – but in different ways, a new meta-study suggests.
In women, aspirin reduces strokes, and in men it cuts down on heart attacks. But there are no statistically significant benefits the other way round, according to the analysis.
“It appears that women respond differently to a given dose of aspirin than men,” says David Brown, a cardiologist at the Stony Brook School of Medicine in New York, US, and one of the authors. “Everything about the study is telling us that there’s a gender difference and we don’t understand it.”
In people who already have cardiovascular disease, the benefits of low-dose aspirin are well-established – in both sexes. Aspirin’s cardiovascular effects are exerted by blocking the synthesis of thromboxane A2, a substance that causes the blood to clot. Even a single 100 milligram dose can be effective.
But in people with moderate risk, the picture is less clear. Studies seem to indicate a reduction in coronary events, but most studies included few, if any, women. Brown and colleagues were interested in knowing if moderate-risk women would benefit to the same degree as men.
Their analysis of six prospective, randomised, controlled studies, with a total of 95,456 subjects - 51,342 being women - showed that aspirin therapy reduced cardiovascular events in both men and women.
But there was an odd discrepancy. Among men, the risk of heart attack was down by 32% in aspirin-takers, but in women, aspirin had no effect on heart attacks at all. Rather, it worked primarily by cutting their risk of stroke by 17%. But aspirin did nothing to reduce stroke in men.
The researchers point out that, whereas men tend to have more heart attacks than strokes, women have slightly more strokes than heart attacks. But there is likely to be a biological difference as well, they say, speculating that women may metabolise aspirin differently than men. Brown says the findings underscore how important it is to include a large cross-section of populations in clinical drug trials.
Currently, the American Heart Association recommends that both men and women at moderate risk of cardiovascular problems take low-dose aspirin on a daily basis, but Brown says the European Society of Cardiology only recommends aspirin to the men of the moderate risk group.
“The AHA guidelines were written without data,” Brown claims, and adds that his study now supports that idea that both sexes can benefit from aspirin therapy – though not in the way that was presumed.
He cautions that individuals start aspirin therapy only after consulting a doctor – in asymptomatic people the benefits only slightly outweigh the dangers of excessive bleeding.
Journal reference: Journal of the American Medical Association (vol 295, p 306)