Medroxyprogesterone acetate enhances the spinal bone mineral density response to oestrogen in late post-menopausal women

OBJECTIVES The relative contributions of administered oestrogen and progestin to protection of the post-menopausal skeleton remain unclear. We have compared the effect on spinal bone mineral density of continuous combined oestrogen/medroxyprogesterone therapy with that of unopposed oestrogen in late post-menopausal women. DESIGN Observational study. SUBJECTS Seventy-three osteoporotic post-menopausal women attending the Auckland Hospital Bone Clinic. Twenty-three hysterectomized women were treated with unopposed oestrogen (0.625 mg oral conjugated oestrogens daily), and 50 non-hysterectomized women were treated with continuous combined oestrogen/medroxyprogesterone therapy (5 mg medroxyprogesterone acetate and 0.625 mg oral conjugated oestrogens daily). MEASUREMENTS Baseline and one-year measurements of lumbar spine bone mineral density were performed using dual-energy X-ray absorptiometry. RESULTS After one year of therapy, spinal bone mineral density increased by 6.6% (95% confidence interval 5.6-7.6, P < 0.001 vs baseline) in the combined oestrogen/ medroxyprogesterone therapy group, compared to 4.0% (Cl 2.4-5.7, P < 0.001 vs baseline) in the unopposed oestrogen group (difference between means 2.6% (CI 0.8-4.4, P < 0.01). CONCLUSION In osteoporotic post-menopausal women, one year of continuous combined oestrogen/medroxyprogesterone therapy is associated with a 65% greater increment in spinal bone mineral density than is observed in response to unopposed oestrogen. The prescription of combined oestrogen/progestin therapy should be considered in osteoporotic post-menopausal women who have undergone hysterectomy, in order to maximize the skeletal protection provided by hormone replacement therapy.