December 4th, 2014
No Evidence to Support Routine Use of Aspirin in Women for Primary Prevention
Larry Husten, PHD
Although once widely recommended, aspirin for primary prevention has lost favor in recent years, as the large number of bleeding complications appeared to offset the reduction in cardiovascular events. But at the same time evidence has emerged demonstrating the long-term effect of aspirin in preventing colorectal cancer, leading some to think that the risk-to-benefit equation for aspirin should be reconsidered.
Investigators in the Women’s Health Study therefore analyzed long-term followup data from 27,939 women who were randomized to placebo or 100 mg aspirin every other day. They then calculated the 15-year risk for cardiovascular disease and colorectal cancer for the women in the study. In the overall study population aspirin use led to very small reductions in absolute risk for cardiovascular disease and colorectal cancer, resulting in NNTs (number need to treat) of 371 and 709. This tiny benefit occurred at the expense of the increase in gastrointestinal bleeding, reflected in the NNH (number needed to harm) of 133.
However, in women who were 65 or older the cardiovascular benefits of aspirin were more pronounced, with a 3.11% reduction in absolute risk at 15 years yielding a NNT of 29. GI bleeding was also increased in this older group,”but this increase was relatively smaller than the decrease in CVD, especially if bleeding is given less weight than CVD and cancer,” wrote the authors.
In their paper published in Heart, the authors conclude that aspirin for primary prevention “is ineffective or harmful in the majority of women with regard to the combined risk of CVD, cancer and major gastrointestinal bleeding.” However, they state that “selective treatment” in women 65 and older may be reasonable.
A major problem in this analysis is the fact that predicting coronary risk in women is a very difficult task using conventional risk factors. If however, if risk was assessed by the dramatically accurate metric of coronary calcium imaging, we could give aspirin to women who would benefit from it and avoid those without coronary disease therefore without any real benefit from ASA.