Current Use of Unopposed Estrogen and Estrogen Plus Progestin and the Risk of Acute Myocardial Infarction Among Women With Diabetes: The Northern California Kaiser Permanente Diabetes Registry, 1995–1998

Background—Little is known about hormone replacement therapy (HRT) and risk for myocardial infarction (MI) in diabetic women. We examined associations of current HRT, estrogen dosage, and time since HRT initiation with risk of acute MI in diabetic women. Methods and Results—Cox proportional hazards models, with current HRT modeled as a time-dependent covariate, were used to assess the 3-year risk of MI. Among 24 420 women without a recent MI (mean age 64.9 years), 1110 incident MIs were identified. After adjustment for cardiovascular risk factors, current HRT was associated with reduced MI risk (relative hazard [RH] 0.84, 95% CI 0.72 to 0.98). The RH for MI associated with current estrogen plus progestin use was 0.77 (95% CI 0.61 to 0.97), and the RH for MI associated with current unopposed estrogen use was 0.88 (95% CI 0.73 to 1.05). Women were at reduced MI risk if they were taking a low or medium dose of estrogen (equivalent to <0.625 or 0.625 mg of conjugated estrogen, respectively) but not a high dose (>0.625 mg of conjugated estrogen or its equivalent). Among those whose current use of HRT was <1 year, the RH for MI was 1.03 (95% CI 0.74 to 1.44), whereas among users for ≥1 year, the RH was 0.81 (95% CI 0.66 to 1.00). Among 580 women with a recent MI (mean age 69.2 years), 89 recurrent MIs were identified. An increased risk of recurrent MI was observed among current HRT users (RH 1.78, 95% CI 1.06 to 2.98), which was higher among those with current use for <1 year (RH 3.84, 95% CI 1.60 to 9.20). Conclusions—In women without a recent MI, use of estrogen plus progestin was associated with decreased risk of MI. However, HRT was associated with increased risk of MI in women with history of a recent MI. Data from clinical trials in diabetic women are needed.