Objective: Because the Women's Health Initiative randomized controlled trial (WHI RCT) primarily studied older women, it is unresolved whether hormone therapy might prevent coronary heart disease in younger women. Given the similarity between our UK General Practice Research Database (GPRD) study of older women and the WHI RCT, the GPRD methodology was used to study a cohort of younger women.
Design: Women ages 50 to 55 years were investigated using data from the GPRD to simulate the WHI RCT in a manner similar to our initial study of older women. This study compared 30,102 unexposed and 20,654 exposed women treated with conjugated estrogens and norgestrel.
Results: Myocardial infarction was not altered significantly by hormone therapy (adjusted hazard ratio 0.91; 95% CI, 0.69-1.20). Stroke, venous thromboembolic events, breast cancer, and hip fracture were similar to both the GPRD study of older women and the WHI RCT. Although death was decreased in the total cohort, similar to older women, it was not altered significantly in a subset without missing covariate data.
Conclusion: The similar results of the GPRD studies in younger and older women and between the GPRD and the WHI RCT suggest that hormone therapy does not prevent coronary heart disease in younger postmenopausal women. This study also demonstrates that investigation using a primary care electronic medical record database can expand the generalizability of findings from an RCT.