A Prospective Study of Aspirin Use and Primary Prevention of Cardiovascular Disease in Women

OBJECTIVE: The aim of the study was to examine prospectively the association between regular aspirin use and the risk of a first myocardial infarction and other cardiovascular events in women. DESIGN: Prospective cohort study including 6 years of follow-up. SETTING: Registered nurses residing in 11 US states. PARTICIPANTS: US registered nurses (n = 87,678) aged 34 to 65 years and free of diagnosed coronary heart disease, stroke, and cancer at baseline. Followup was 96.7% of total potential person-years of follow-up. MAIN OUTCOME MEASURES: Incidence of myocardial infarction, stroke, cardiovascular death, and all important vascular events. RESULTS: During 475,265 person-years of follow-up, we documented 240 nonfatal myocardial infarctions, 146 nonfatal strokes, and 130 deaths due to cardiovascular disease (total, 516 important vascular events). Among women who reported taking one through six aspirin per week, the age-adjusted relative risk (RR) of a first myocardial infarction was 0.68 (95% confidence interval CI, 0.52 to 0.89; P = .005), as compared with those women who took no aspirin. After simultaneous adjustment for risk factors for coronary disease, the RR was 0.75 (95% CI, 0.58 to 0.99; P = .04). For women aged 50 years and older, the age-adjusted RR was 0.61 (95% CI, 0.45 to 0.84; P = .002) and the multivariate RR was 0.68 (95% CI, 0.50 to 0.93; P = .02). We observed no alteration in the risk of stroke (multivariate RR = 0.99; P = .94). The multivariate RR of cardiovascular death was 0.89 (P = .56) and of important vascular events was 0.85 (P = .12). When examined separately, the results were nearly identical for the subgroups who took one through three and four through six aspirin per week. Among women who took seven or more aspirin per week, there were no apparent reductions in risk. CONCLUSIONS: The use of one through six aspirin per week appears to be associated with a reduced risk of a first myocardial infarction among women. A randomized trial in women is necessary, however, to provide conclusive data on the role of aspirin in the primary prevention of cardiovascular disease in women.