Daily aspirin more effective than alternate-day aspirin as primary prevention of cardiovascular disease, colon cancer in elderly women

Taking aspirin on alternate days is ineffective in preventing cancer or cardiovascular disease in most women, a new analysis of Women's Health Study data found. For many women 65 years of age or older, the benefits of daily aspirin for primary prevention of colon cancer and cardiovascular disease still outweigh the associated bleeding risk.

Researchers used data on 27,939 women from the Women's Health Study to compare the effects of 100 mg of aspirin on alternate days to placebo on the outcomes of cancer, cardiovascular disease (CVD), and major gastrointestinal bleeding. The women were at least 45 years old, had no history of CVD or cancer, and were followed for a median of 10.1 years. The researchers developed models to predict the 15-year absolute risk reduction from taking aspirin and evaluated which treatment strategies led to best outcomes: Treat none, treat everyone, treat only women age 65 years or older, or use individualized prediction-based treatment. Results were published online Dec. 4 in Heart.

Aspirin use was associated with a small decreased risk for CVD (15-year absolute risk reduction [ARR], 0.27%; 95% CI, 0.06% to 0.86%; number needed to treat [NNT], 371) and colorectal cancer (15-year ARR, 0.14%; 95% CI, 0.02% to 0.59%; NNT, 709). The protective effect of aspirin increased with age. Aspirin had no effect on non-colorectal cancer, but it was associated with an increased risk of gastrointestinal bleeding (GI) in all women (15-year absolute risk increase, 0.75%; 95% CI, 0.50% to 1.00%; number needed to harm, 133). Thus, once GI bleeding was taken into account, aspirin resulted in no treatment benefit in most women, the authors noted.

There was, however, a stronger protective effective of aspirin on CVD in women age 65 years and older (15-year ARR, 3.11%; 95% CI, 1.67% to 5.27%; NNT, 29). The risk of GI bleeding was also higher in this older group, but the increase was smaller than the decrease in CVD risk, suggesting a net benefit for this group.

“In many women ≥65 years of age the benefits of aspirin with regard to cancer and particularly CVD risk outweigh the increased bleeding risk, especially if bleeding events are considered to be less important,” the authors wrote. For the majority of women, however, alternate-day use of low-dose aspirin for primary prevention is ineffective—even harmful—given the combined risk of CVD, cancer, and major GI bleeding, they concluded.