Boston, MA- While aspirin is used in the treatment of myocardial infarction and as a secondary prevention in cardiovascular disease, its role as a primary form of prevention remained unknown. In the Women’s Health Study, Paul Ridker et al from Brigham and Women’s Hospital at Harvard Medical School, evaluated the lowest dose of aspirin that would have a cardioprotective effect. The study was published in the March 31,2005 issue of The New England Journal of Medicine and found that aspirin lowered the risk of stroke without affecting the risk of myocardial infarction or death from cardiovascular causes.

Evidence of the effects of aspirin in women is necessary because cardiovascular disease is the leading cause of death in both men and women. The effects of aspirin in women and its prophylactic use for stroke and myocardial infarction is the primary concern in the Women’s Health Study. The study randomly assigned 39,876 initially healthy women 45 years of age or older to receive 100 mg of aspirin on alternate days or placebo. They were monitored for 10 years for a first major cardiovascular event, such as nonfatal myocardial infarction, stoke or death from cardiovascular causes.

Results from follow-up indicate 477 major cardiovascular events in the aspirin group, as compared to 522 in the placebo group, resulting in a reduction of 9 percent (relative risk, 0.91; 95 percent confidence interval, 0.80-1.03). There was a 17 percent reduction in the risk of stoke in the aspirin group as compared to placebo (relative risk, 0.83; 95 percent confidence interval,0.69 to 0.99; P=0.04), owing to a 24 percent reduction in the risk of ischemic stroke (relative risk, 0.76; 95 percent confidence interval 0.63 to 0.93; P=0.009). The increase in risk of hemorrhagic stroke was non-significant (relative risk, 1.24; 95 percent confidence interval, 0.82 to 1.87; P=0.31). Aspirin had no significant effect on the risk of fatal or nonfatal myocardial infarction (Relative Risk, 1.02; 95 percent confidence interval 0.84 to 1.25; P=0.83) or death from cardiovascular causes (relative risk, 0.95; 95 percent confidence interval, 0.74 to 1.22; P=0.68). It was significant that gastrointestinal bleeding requiring transfusion was more frequent in the aspirin group than in the placebo group (relative risk 1.4; 95 percent confidence interval, 1.07 to 1.83; P=0.02).

Overall, in this large, placebo-controlled, primary-prevention trial, a prophylactic dose of 100 mg every other day is associated with a reduction of total stroke and ischemic stroke, a nonsignificant reduction in the risk of major cardiovascular events, a nonsignificant increase in the risk of hemorrhagic stoke and non significant effect on the risk of myocardial infarction or death from cardiovascular causes.

Co-authors:  Nancy R. Cook, Sc.D., I-Min Lee, M.B., B.S., David Gordon, M.A., J. Michael Gaziano, M.D., Joann E. Manson, M.D., Charles H. Hennekens, M.D., and Julie E. Buring, Sc.D.