Estrogen replacement therapy and protection from acute myocardial infarction.

As part of a longitudinal study of a southern California retirement community begun in June 1981, 8841 women 44 to 101 years old completed a health survey questionnaire. As of January 1, 1987, 1019 deaths had occurred among these women, who had contributed 40,919 years of follow-up. Women who had used estrogen replacement therapy had a relative risk of death due to all causes of 0.80 compared with women who had never used estrogens (p = 0.0005). Much of this reduced mortality rate was due to a marked reduction in the death rate of acute myocardial infarction among users of estrogen (55 deaths) compared with nonusers (94 deaths; relative risk = 0.59, p = 0.002). This lower acute myocardial infarction death rate was maintained even in the presence of other known risk factors for coronary artery disease. There was no substantial effect of dose or duration of estrogen use on risk, but the relatively small number of deaths limited our ability to estimate these effects accurately. Current users (those who were using estrogen at the time of the initial questionnaire) had a relative risk of 0.47 and past users had a risk of 0.62 compared with women who had never used estrogen (p = 0.003 for trend). A reduced hospitalization rate for acute myocardial infarction was similarly observed for estrogen users compared with nonusers (relative risk = 0.72, p = 0.03).