Hormone replacement therapy and incidence of acute myocardial infarction -A population-based nested case-control study

Background-Epidemiological studies suggest a decreased risk of coronary hea rt disease (CHD) in healthy women taking hormonal replacement therapy (HRT) . Whether this effect is shared by oral and transdermal preparations is unk nown. Methods and Results-We conducted a population-based case-control study nest ed in a cohort of women 50 to 74 years of age without cardiovascular diseas e history in the United Kingdom. Among 164 769 women from the General Pract ice Research Database (January 1, 1991, to December 31, 1995), we identifie d 1242 first acute myocardial infarctions (AMI) and confirmed 1013 after me dical record review. We randomly selected 5000 age-frequency-matched contro l subjects. AMI incidence was 1.6 per 1000 person-years; 13% and 17% of cas es and control subjects used HRT within 6 months before the index date. Ris k factor and comorbidity-adjusted OR of AMI far current-recent HRT users co mpared with nonusers was 0.72 (95% CI 0.59 to 0.89). The OR was similar wit hin 30 days before the index date. The beneficial effect was present after 1 year of use (OR 0.68; 95% CI 0.53 to 0.86), with no increase in risk with in the first year. ORs for unopposed and opposed therapy were 0.52 (95% CI 0.35 to 0.78) and 0.79 (95% CI 0.59 to 1.08); 79% and 21% used oral and tra nsdermal therapy. The protective effect was present at medium-high doses of estrogens with ORs for oral and transdermal therapy of 0.63 (95% CI 0.46 t o 0.86) and 0.62 (95% CI 0.37 to 1.06) and ceased after 2 to 3 years since stopping HRT. Conclusions-Results are consistent with those previously reported in women without CHD who were taking oral HRT and, although based on few users, sugg est that transdermal therapy might have similar cardioprotective effects.