Post menopausal hormone replacement therapy and risk of acute myocardial infarction - A case control study of women in the East Midlands, UK

Aims: To examine the relationship between hormone replacement therapy (HRT) and acute myocardial infarction (AMI) adjusting for coronary risk factors and social and behavioural confounders that might indicate a healthy user effect and could account for the discrepancy between randomized and observational studies of HRT use. Methods: A case-control study of 864 women aged between 35-65 suffering an AMI with two age matched community controls from the same geographical area. Information was collected by interview and from general practitioner records. Conditional logistic regression was used to calculate odds ratios (OR) adjusted for diabetes, hypertension, smoking, alcohol, social class, family history and a health conscious behaviour score. Results: HRT use was recorded for 34% of non-fatal AMI cases and 39% of controls with the adjusted OR for ever-use of HRT versus never-use being 0.74 (95% CI 0.55-0.99). The pattern of risk of AMI was similar for oestrogen only and combined HRT. During the first 12 months of HRT use there was a small increase in risk of AMI with the adjusted OR being 1.14 (0.72-1.80). HRT use for 13-60 months was associated with a small reduction in AMI risk (adjusted OR 0.85, 0.55-1.29). Only HRT used for >60 months was associated with a substantial risk reduction (adjusted OR 0.42, 0.24-0.73). Data for deceased cases and controls showed a similar pattern. Conclusion: HRT use whether as oestrogen only or combined hormones was only associated with a significant reduction in risk when used for greater than 60 months. These findings could reflect a dual effect of HRT on AMI risk by prothrombotic and anti-atherogenic mechanisms. Neither oestrogen only or combined HRT can be recommended for prevention of coronary artery disease.