Changes in bone density in women starting hormone replacement therapy compared with those in women already established on hormone replacement therapy.

It is well established that hormone replacement therapy (HRT) will prevent postmenopausal loss of bone. However, it is not known to what extent HRT will continue to affect bone mineral density (BMD) in women established on HRT compared with those commencing treatment. We recruited 48 healthy early postmenopausal women into a prospective, comparative study. Twenty-nine women had never taken HRT (group A) whilst 19 women were already taking HRT (group B) (conjugated equine oestrogens, 0.625 mg daily; mean (+/- SD) years of use 2.2 (1.5) years). All of the women were started on, or switched to, micronized 17 beta-oestradiol (2 mg/day) continuously with dydrogesterone (10 mg/day) for the first 14 days of each cycle. BMD measurements were performed at the lumbar spine and proximal femur using dual-energy X-ray absorptiometry (DXA) at baseline and after 12 and 24 months of treatment. Group A showed a significantly greater increase in lumbar spine BMD after 12 months (mean +/- SD) = 5.3 (4.6)%) compared with group B (mean +/- SD) = 2.1 (2.1)%) and 24 months of treatment (group A, mean (+/- SD) = 6.4 (5.2)%; group B, mean (+/- SD) = 2.3 (2.6)%; both p < 0.01) and 24 months of treatment (r = -0.05). These data demonstrate that HRT has the greatest effect on BMD when it is first administered, especially in those women with low BMD, but improvements may still be observed in women continuing HRT in the longer term.