DURATION OF ESTROGEN REPLACEMENT THERAPY IN RELATION TO THE RISK OF INCIDENT MYOCARDIAL-INFARCTION IN POSTMENOPAUSAL WOMEN

Background: There is little information about whether an increasing du ration of estrogen replacement therapy is associated with a declining risk for myocardial infarction in postmenopausal women. Objective: To conduct a population-based, case-control study among enrollees of the Group Health Cooperative (GHC) of Puget Sound, Seattle, Wash. Subjects and Methods: Case subjects were all postmenopausal women who were enr olled in the GHC with an incident fatal or nonfatal myocardial infarct ion from July 1986 through December 1993. Control subjects were a stra tified random sample of postmenopausal women who were enrolled in the GHC without myocardial infarction and matched to case subjects by age and calendar year. We reviewed the medical records of the 850 case sub jects and 1974 control subjects and conducted telephone interviews wit h consenting survivors. Use of estrogen or estrogen and progestin was assessed using GHC's computerized pharmacy database. Results: Among wo men who were currently using estrogen, a longer duration of use was in versely associated with a risk for myocardial infarction after adjustm ent for age, year of identification, diabetes mellitus, angina, and sm oking. For categories of increasing duration of estrogen use (never, > 0-<1.8 years, 1.8-<4.2 years, 4.2-<8.2 years, and greater than or equa l to 8.2 years), the odds ratios for myocardial infarction were 1.00 ( reference), 0.91, 0.70, 0.65, and 0.55 (for trend among the current us ers, P=.05). Among women who had used estrogen in the past, there was no evidence of decreasing risk with increasing duration of estrogen us e. Conclusion: In this study, a long duration of hormone replacement t herapy among women currently using estrogen was associated with a redu ced risk for first myocardial infarction.