Commentary

The landmark 10 year study by Ridker et al of nearly 40 000 initially healthy women found that taking prophylactic low dose (100 mg) aspirin every other day did not confer the same benefits to women as it did to men. Few therapies have separately analysed effects by sex, and the findings lead us to ponder why many of the therapies used for women are not effective or are even harmful. The authors note that the reasons for any sex based differences in the efficacy of aspirin for primary prevention of cardiovascular disease are unclear and require further exploration.

The strengths of the study were that it had a large sample size; was double blinded, randomised, and placebo controlled; and used a single simple intervention and clear outcomes. The treatment and control groups were well balanced in terms of initial characteristics, and follow up for outcome measurement was excellent. The study also considered both risks and benefits. An interesting finding from subgroup analyses was that the women (10% of the study population) who seemed to benefit most were those ⩾65 years of age. In this group, aspirin use led to 44 fewer myocardial infarctions, strokes, or deaths from cardiovascular causes but also to 16 more gastrointestinal haemorrhages requiring transfusion.

The women in the study were generally at low risk for cardiovascular events, and <3% of women in the placebo group had a major cardiovascular event during the 10 year follow up period. Based on the fact that aspirin was more effective in older women and that cardiovascular risk increases with age, it seems sensible to advocate use of low dose aspirin in this group. It is less clear whether aspirin should be used in younger women unless they have high global risk scores. This study offers women additional valuable evidence to help inform their choices about aspirin for primary prevention of cardiovascular disease.