Persistence with oral and transdermal hormone replacement therapy and hospitalisation for cardiovascular outcomes

Background: The effect of persistence with transdermal and oral administrations of hormone replacement therapy (HRT) on the risk of hospitalisation for cardiovascular disease, and the role of income as potential confounder, were explored in a large population-based cohort study. Methods: Seventy-eight thousand eight hundred and seventy-five women resident in the Italian Lombardy Region aged 45-65 years who received at least one HRT prescription during 1998-2000 were followed until December 2003. The 828 cohort members who experienced at least one hospitalisation for a circulatory system disease were identified from the Regional hospital discharge database. The Regional prescription drug database was used to assess cumulative persistence with hormone treatment during follow-up. Data on individual taxable income was also obtained for women resident in the city of Milan. A proportional hazards model was fitted to estimate the association between cumulative time-dependent persistence with HRT and cardiovascular risk. Results: Compared with women who took HRT for less than 6 months, those exposed for more than 3 years to HRT as a whole, and to transdermal and oral HRT, respectively, showed hazard ratios of 0.65 (95% confidence interval: 0.45, 0.92), 0.53 (0.34, 0.82), and 1.15 (0.47, 2.79). CVD reducing potential of HRT disappeared when estimates were adjusted for income being hazard ratio associated with long-term use 0.94 (0.52, 1.71). Conclusions: Evidence that CVD risk associated with long-term hormone treatment varies according to the route of HRT administration, and that economic position confounds the effect of HRT on the risk of cardiovascular hospitalisation, is provided by the current study.