Relation between hormone replacement therapy and ischaemic heart disease in women: prospective observational study.

OBJECTIVE To investigate the risk of ischaemic heart disease and myocardial infarction among women using hormone replacement therapy, especially the potential modifying effect of cardiovascular risk factors. DESIGN Prospective observational study. SETTING Denmark. PARTICIPANTS 19 898 nurses aged 45 and over completing a questionnaire on lifestyle and use of hormone replacement therapy in 1993. MAIN OUTCOME MEASURES All cases of death and incident cases of ischaemic heart disease and myocardial infarction until the end of 1998. RESULTS Current users of hormone replacement therapy smoked more, consumed more alcohol, had lower self rated health, but were slimmer and had a lower prevalence of diabetes than never users. In current users compared with never users, hormone replacement therapy had no protective effect on ischaemic heart disease (hazard ratio 1.2, 0.9 to 1.7) or myocardial infarction (1.0, 0.6 to 1.7), whereas current users with diabetes had an increased risk of death (3.2, 1.4 to 7.5), ischaemic heart disease (4.2, 1.4 to 12.5), and myocardial infarction (9.2, 2.0 to 41.4) compared with never users with diabetes. CONCLUSION Hormone replacement therapy showed no protective effect on ischaemic heart disease, but there was a significantly increased risk of death from all causes and ischaemic heart disease among women with diabetes.