Aspirin Suppresses Platelet Aggregation In Both Women, Men – JAMA

Findings from a study on gender-specific responses to aspirin treatment suggest that low-dose aspirin therapy is beneficial for both men and women in improving cardiovascular health.

Daily low-dose aspirin therapy reduces platelet aggregation, which can produce blood clots, in both men and women, according to a trial published online in the Journal of the American Medical Association March 21.

The study finds a "notable impact of aspirin therapy in women on the COX-1 platelet pathways that are thought to be most protective" against myocardial infarction, Diane Becker, Johns Hopkins University School of Medicine, Baltimore, Md., et al., state.

Women also "experienced the same or greater decreases in platelet reactivity after aspirin therapy," the researchers say.

The findings lead to more questions about gender differences in aspirin's mechanism of action. Some previous research suggests aspirin works differently in women than it does in men.

A meta-analysis recently published in JAMA, which included data from the federal Women's Health Study, showed low-dose aspirin therapy provided protection from MI for men, but not for women (¹ (Also see "Aspirin Therapy Lowers Stroke Risk In Women, MI Risk In Men – JAMA" - Pink Sheet, 23 Jan, 2006.), p. 7).

Investigators from the Women's Health Study had concluded that "resistance to aspirin" was an "unlikely explanation for aspirin therapy's failure to reduce MI risk in women," Becker et al. point out. The "notable impact" of aspirin therapy on the COX-1 platelet pathway in the current study provides support for that conclusion, they add.

The Johns Hopkins study is "believed to be the first direct comparison of blood cell testing in both sexes" of low-dose daily aspirin therapy, according to a same-day release from the university.

"Women are clearly benefiting from taking aspirin and should continue to take it to improve their cardiovascular health," Becker stated. "Aspirin has been proven by all previous studies to lower the risk of stroke and, as our latest findings show, it also reduced platelet aggregation that can lead to potentially fatal clots in blood vessels," she said.

The trial tested the blood of 571 men and 711 women who had no history of heart disease, but who were considered at a slightly increased risk because they had a sibling with documented coronary heart disease events before the age of 60, Becker et al. explain.

The study was performed as part of the ongoing Genetic Study of Aspirin Responsiveness (GeneSTAR) study.

Participants were given 81 mg of aspirin daily for 14 days. Blood samples were taken for analysis at baseline and after 14 days of aspirin therapy. Study authors conducted and analyzed more than 200 different tests of platelet reactivity.

Platelet aggregation was higher for women than men at baseline and remained slightly higher even after aspirin therapy, the researchers point out.

However, men and women presented similar inhibition in pathways directly dependent on COX-1, Becker et al. state.

"Overall, although sex differences were often statistically significant, the magnitude of the differences was small," the researchers maintain.

The study's major limitation was the "lack of prospective data linking measure of platelet reactivity to aspirin to subsequent cardiovascular disease," according to Becker et al.

It is unclear how closely the study's ex vivo tests of platelet function on participants' blood samples would replicate in vivo platelet activity, they state.

Thus, the "overall predictive value for incident cardiovascular events" similarly remains unknown.

However, the findings do show that "aspirin does what it is supposed to do in both men and women," according to study co-author Nauder Faraday, MD.

"Further research is required to get a definitive answer as to whom aspirin really benefits, under what circumstances it does work and does not work, and just how much is required in different people," he said.

- Jessica Lake