Effect of progestin therapy on cortical and trabecular bone: comparison with estrogen.

Purpose: To determine the effect of progestin therapy on bone mineral density in postmenopausal women and to compare its effects to those of estrogen.
Subjects and Methods: A prospective, randomized clinical trial was performed in 81 postmenopausal women aged 51.7 +/- 4.4 years (mean +/- SD). They were assigned to one of four groups: Provera 20 mg, Premarin 0.6 mg, Premarin 0.3 mg plus Provera 10 mg, and a placebo. In addition, all women received calcium supplementation, if necessary, to a calcium intake of 1,000 mg/day. We used single- and dual-photon absorpiometry, metacarpal radiogrammetry, and computed axial tomography to measure bone mineral density in the total skeleton, spine, radius, and metacarpal.
Results: Women receiving placebo lost bone at all sites (p less than 0.01). The Provera-treated group showed no change in total body calcium, but there were decreases in radial density (p less than 0.01), metacarpal cortex (p less than 0.01), and spine density (p less than 0.01). The Premarin-treated group had an increase in spine density and total body density (p less than 0.05), but a decrease in radial density (p less than 0.05). The Premarin-plus-Provera group showed no change in spine density, total body calcium, or radial density but had a decrease in metacarpal cortex (p less than 0.01).
Conclusions: Compared to placebo, Provera reduced the rate of loss in cortical areas of the skeleton, but not in the spine, which contains more trabecular bone. In contrast, Premarin reduced the rate of loss in both cortical and trabecular areas of the skeleton. The low-dose combination of Premarin plus Provera was similar in its effect on bone to that of Premarin alone, suggesting that there may be a synergistic effect of this hormone combination on bone. Serum cholesterol levels decreased with Provera, Premarin, and the combination of both, whereas levels of serum triglycerides increased with Premarin treatment, decreased with the Provera regimen, and were unchanged with the combination therapy. Provera does not adversely affect the lipid profile.