Introduction

Hormone therapy (HT) is commonly prescribed for the relief of climacteric symptoms in post-menopausal women; 54% (620490) of women enrolled in the Million Women Study1 in the UK (mean age 56 years) have tried it and 31% (358252) use it. Observational studies have shown oral HT is associated with lower rates of cardiovascular disease in post-menopausal women2; however randomised controlled trials (RCTs) have presented mixed results. The 2002 publication of the Women's Health Initiative I (WHI I) reported an association between combined oestrogen and progestin use and increased rates of both coronary heart disease and stroke. Subsequent publication of the Women's Health Initiative II (WHI II) reported an association between oestrogen and increased rates of stroke. These publications, and the significant publicity that they received, led to a reduction in prescriptions of oral HT. It also led to several RCTs assessing HT and cardiovascular outcomes stopping before their planned end date.

However, post hoc analysis of the WHI data has suggested that associations between oral HT and cardiovascular outcomes are not uniform across all age groups. The mean ages at recruitment in WHI I and WHI II were early to mid-60s; more than a decade after the mean age of initiation of menopause, when post-menopausal women most commonly suffer from climacteric symptoms. This subgroup analysis demonstrated there was a trend to reduced likelihood of cardiovascular outcomes in women who started HT before the age of 60.3 In 2012, the Danish Osteoporosis Prevention Study (DOPS) was published. It was designed to assess the effect of oral HT on osteoporosis and cardiovascular outcomes and …