The risk of acute myocardial infarction after oestrogen and oestrogen-progestogen replacement.

Abstract

To determine the relative risk of developing a first acute myocardial infarction after treatment with oestrogens alone or oestrogen-progestogen combinations. Prospective cohort study utilizing a prescription-based and record linkage system for a follow-up period from 1977 to 1983. Average individual observation time was 5.8 years. The entire female population of the Uppsala Health Care Region (1.4 million inhabitants), one-sixth of the total Swedish population. 23,174 women aged 35 years and older, identified from pharmacy records as having been prescribed non-contraceptive oestrogens during 1977-1980. Admissions to hospitals for first acute myocardial infarctions. Overall, 227 cases of a first acute myocardial infarction were observed as against 281:1 expected, RR = 0.81 (95% confidence limits 0.71 to 0.92). Women who were younger than 60 years at entry into the study and prescribed oestradiol compounds (1-2 mg) or conjugated oestrogens (0.625-1.25 mg) showed a significant 30% reduction of the relative risk (RR = 0.69, 0.54 to 0.86). Those prescribed a combined oestradiol-levonorgestrel brand also demonstrated a significantly lowered relative risk (RR = 0.53, 0.30 to 0.87). The risk estimates were near unity during the first year of follow-up but decreased during subsequent years. Exposure to the weak oestrogen oestriol did not alter the risk. Hormonal replacement therapy with oestrogens alone, and maybe also when cyclically combined with progestogens, can reduce the risk of acute myocardial infarction.