Women's Health Study: Low-Dose Aspirin in Primary Prevention - Women's Health Study: Low-Dose Aspirin in Primary Prevention


The goal of the trial was to evaluate treatment with low-dose aspirin for the primary prevention of cardiovascular disease in women.


Treatment with low-dose aspirin compared with placebo will be associated with a reduction in primary cardiovascular events in women.

Study Design

Study Design:

Patients Enrolled: 39,876
Mean Follow Up: Mean 10.1 years
Mean Patient Age: Mean age 55 years
Female: 100

Patient Populations:

Age ≥45 years; no history of coronary heart disease, cerebrovascular disease, cancer (except nonmelanoma skin cancer), or other major chronic illness; no history of side effects to any of the study medications; not taking aspirin or nonsteroidal anti-inflammatory medications more than once a week (or were willing to forego their use during the trial); not taking anticoagulants or corticosteroids; and not taking individual supplements of vitamin A, E, or beta carotene more than once a week

Primary Endpoints:

Combined endpoint of nonfatal MI, nonfatal stroke, and total cardiovascular death, as well as incidence of total malignant neoplasms of epithelial cell origin

Drug/Procedures Used:

Following a three-month placebo run-in period to ensure good compliance, female health professionals over age 45 participating in the study were randomized to treatment with low-dose aspirin (n=19,934; 100 mg on alternate days) or placebo (n=19,942). Women were also randomized in a factorial design to treatment with vitamin E or placebo. Participants were treated and followed for a mean of 10.1 years. Participants were followed for the occurrence of nonfatal myocardial infarction (MI), nonfatal stroke, and cardiovascular death. Events were reviewed by an Endpoints Committee of physicians who were blinded to treatment assignment.

Principal Findings:

Baseline characteristics were well matched between the two treatment groups. The primary composite endpoint of major cardiovascular events occurred in 477 women in the aspirin group and 522 in the placebo group (relative risk [RR] 0.91, 95% confidence interval [CI] 0.80-1.03, p=0.13). Among the individual components of the composite endpoint, there was no difference in MI (n=198 vs. n=193, RR 1.02, 95% CI 0.84-1.25, p=0.83) or death from cardiovascular causes (n=120 vs. n=126, RR 0.95, 95% CI 0.74-1.22, p=0.68), but total stroke was lower in the aspirin group (n=221 vs. n=266, RR 0.83, 95% CI 0.69-0.99, p=0.04), due to a reduction in ischemic stroke (n=170 vs. n=221, RR 0.76, p=0.009).

Hemorrhagic stroke occurred in 51 women in the aspirin group and 41 women in the placebo group (RR 1.24, p=0.31). Transient ischemic attack was lower in the aspirin group (n=186 vs. n=238, RR 0.78, p=0.01). Gastrointestinal bleeding requiring transfusion occurred in 127 women in the aspirin group versus 91 in the placebo group (RR 1.40, p=0.02). There was no difference by treatment group in total cancer (RR 1.01, p=0.87), breast cancer (RR 0.98, p=0.68), or colorectal cancer (RR 0.97, p=0.83).

In the subgroup analysis, the primary endpoint was lower in women age ≥65 years (n=4,097) (RR 0.74, p=0.008), but did not differ in women <65 years (p<0.001 for interaction). Additionally, the primary endpoint was lower in women who were former or never smokers (RR 0.80, p=0.003), but was higher in current smokers (RR 1.30, p=0.03; p<0.001 for interaction).


Among initially healthy women, treatment with low-dose aspirin was not associated with a significant difference in the primary endpoint of major cardiovascular events compared with placebo at a mean 10-year follow-up.

Low-dose aspirin has been shown to be effective for secondary prevention following acute coronary syndrome, but data for primary prevention with aspirin in women were limited. The Physicians' Health Study, a randomized trial of aspirin for primary prevention conducted in male physicians, showed a reduction in MI and a trend toward an increase in total stroke, unlike the present trial in women, which showed no difference in MI and a reduction in total stroke.

It is unclear why gender-related differences in aspirin therapy for primary prevention may exist. Benefit with aspirin therapy was observed in the subgroup of women age ≥65 years and nonsmokers.


Ridker PM, Cook NR, Lee IM, et al. A randomized trial of low-dose aspirin in the primary prevention of cardiovascular disease in women. N Engl J Med 2005 352:1293-1304.

Cook NR, et al. Low-Dose Aspirin in the Primary Prevention of Cancer. JAMA. 2005;294:47-55.

Presented by Dr. Paul M. Ridker at the March 2005 ACC Annual Scientific Session, Orlando, FL.

Keywords: Risk, Myocardial Infarction, Acute Coronary Syndrome, Stroke, Skin Neoplasms, Follow-Up Studies, Atherosclerosis, Ischemic Attack, Transient, Vitamin E, Platelet Aggregation Inhibitors, beta Carotene, Women's Health, Breast Neoplasms, Primary Prevention, Secondary Prevention, Vitamin A, Colorectal Neoplasms, Confidence Intervals

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