To determine whether the effect of MHT use on each of the cardiac outcomes differed by age, multivariable regression models were constructed with a cross-product of age and MHT fitted as an interaction term. Co-variates included: duration of MHT use fitted as thirds, ethnicity, height, weight, systolic blood pressure, diastolic blood pressure, smoking status, regular alcohol use, presence of raised cholesterol, presence of diabetes, Townsend deprivation index and income (Model 2). Interactions were tested using age as a continuous variable. For ease of interpretation we also fitted the interaction using tertile of age and presented effect sizes for MHT use by tertile.