Background: Cardiovascular disease and cancer are the leading causes of death in women in the United States. Studies have shown that aspirin reduces cardiovascular events and colonic polyps; however, aspirin's impact on mortality is unclear, particularly in women. Although a 2005 study showed that low-dose aspirin did not influence mortality, the study assessed only a single dose, and the number of deaths during the study was limited. The Nurses' Health Study also did not show aspirin therapy as benefiting mortality; however, it had a short-term follow-up period (six years) and was limited by a small number of deaths. Chan and associates used the Nurses' Health Study to assess the effect of aspirin therapy on mortality in women during 24 years of follow-up.

The Study: The Nurses' Health Study included a prospective survey of 121,701 married nurses in the United States. The original surveys were completed in 1976, and subsequent surveys were mailed to the nurses biennially. Regular aspirin use was first assessed in the survey in 1980. Low-dose aspirin was added to the survey in 1992. Mortality data were collected from 1980 to June 1, 2004, using the National Death Index and information from next of kin; 98 percent of the deaths were included in the analysis. Causes of death were established using death certificates and medical records. The main outcome measure was all-cause deaths. In addition, deaths from cardiovascular disease; stroke; or lung, breast, and colorectal cancers were analyzed. Deaths were compared with a control group made up of participants who were alive at the end of the study.

Results: Of the 79,439 participants, 9,477 died during the study. Women who regularly used aspirin had a relative risk of death from any cause of 0.75 (95% confidence interval, 0.71 to 0.81), compared with women who did not take aspirin. In aspirin users, the relative risk of death related to cardiovascular disease was less than that of cancer-related death (0.62 versus 0.88). A significant reduction in cardiovascular disease–related deaths occurred one to five years after initiating aspirin therapy, whereas the reduction in cancer-related deaths occurred after 10 years of aspirin use. Low and moderate doses of aspirin were equally effective in reducing mortality. The greatest benefit of aspirin use occurred in older participants and in those with more cardiac risk factors.

Conclusion: Low and moderate doses of aspirin were associated with a reduction in death from any cause in women, particularly in older women and those with more cardiac risk factors. The reduction in cardiovascular deaths occurred within five years, whereas the reduction in cancer deaths occurred after 10 years of aspirin use.