Estrogen-progestin therapy causes a greater increase in spinal bone mineral density than estrogen therapy - a systematic review and meta-analysis of controlled trials with direct randomization

OBJECTIVE To assess whether progesterone (P4) or osteoblast P4 receptor-acting progestin (P) contributed to estrogen (E) therapy-related increased areal bone mineral density (BMD) in randomized controlled trials (RCT) with direct randomization to estrogen (ET) or estrogen-progestin (EPT) therapy. METHODS Systematic literature searches in biomedical databases identified RCT with direct randomization and parallel estrogen doses that measured spinal BMD change/year. Cyclic P4/P was included in this random effects meta-analysis only if for ≥ half the number of E-days. RESULTS Searches yielded 155 publications; five met inclusion criteria providing eight dose-parallel ET-EPT comparisons in 1058 women. Women averaged mid-50 years, ⟨five years into menopause and took conjugated equine E daily at 0.625 mg with/without 2.5 mg medroxyprogesterone acetate (MPA). The weighted mean EPT minus ET percentage difference in spinal BMD change was +0.68%/year (95% CI 0.38, 0.97%) (P=0.00001). This result was highly heterogeneous (I²=81%) but this may reflect the small number of studies. CONCLUSION Estrogen with an osteoblast P4R-acting progestin (EPT) in these five published RCT provides Level 1 evidence that MPA caused significantly greater annual percent spinal BMD gains than the same dose of ET. These data have implications for management of vasomotor symptoms and potentially for osteoporosis treatment in menopausal women.