Do current regimes of hormone replacement therapy protect against subsequent fractures?

It is now accepted that unopposed oestrogen therapy reduces osteoporotic fractures by about 50%. Although current regimes with added progestogens are thought to act similarly to unopposed oestrogens, no study has yet demonstrated an effect on fractures with the former. Using a retrospective cohort design we studied fracture rates in women attending a menopause clinic for hormone replacement therapy (HRT) and compared them with women derived from the general population. Data were analysed from 1075 women exposed to HRT and 1741 non-exposed postmenopausal women. In all 226 fractures were reported between 1977 and 1986, the commonest site being the distal radius, occurring in 28 of the HRT women and in 37 of the non-exposed women. The incidence density rate for fracture of the distal radius is 3.5/1000 woman-years (wy) in non-exposed women. This was similar to the rate in the HRT women prior to HRT use, the rate falling by 30% after exposure from 3.2 to 2.2/1000 wy. The protective effect on osteoporotic fractures increased progressively with duration of use. After 5 years of use the relative risk fell to 0.5 (95% confidence interval, 0.2-1.2) for all osteoporotic fractures and for the distal radius to 0.18 (95% confidence interval, 0.05-1.3). No similar changes were seen for non-osteoporotic fractures. There were 6 (0.6/1000 wy) reported fractures of the hip in the non-exposed group compared with none in the HRT group (when 1.7 were expected based on non-exposed rates) (p = 0.15).(ABSTRACT TRUNCATED AT 250 WORDS)