LOW-DOSAGE MICRONIZED 17-BETA-ESTRADIOL PREVENTS RONE LOSS IN POSTMENOPAUSAL WOMEN

With the use of a double-blind, randomized, dose-ranging design, we tested during an 18-month period the degree of protection against postmenopausal bone loss afforded by micronized 17-beta-estradiol in dosages of 0.5, 1.0, and 2.0 mg. All subjects received supplementation to ensure a minimum of 1500 mg calcium daily. Fifty-one subjects completed at least 1 year of follow-up bone density measurements by quantitative computed tomography and by single- and dual-photon absorptiometry. In the placebo group spinal trabecular bone density decreased 4.9% annually (p < 0.001), whereas in those taking micronized 17-beta-estradiol bone density tended to increase (annual increases of 0.3% in the 0.5 mg micronized 17-beta-estradiol group, 1.8% in the 1.0 mg micronized 17-beta-estradiol group, and 2.5% in the 2.0 mg micronized 17-beta-estradiol group). After completing the double-blind phase, 41 subjects completed an additional 18 months of follow-up while taking 1.0 mg micronized 17-beta-estradiol. During this time one third of the subjects were randomly assigned to discontinue calcium supplements. Among those who previously received placebo, trabecular bone density increased 4.3% annually, whereas among those who had used micronized 17-beta-estradiol, trabecular bone density response was inversely related to the dosage previously used. Additionally and independently, the level of calcium intake showed a statistically significant correlation with the change in spinal trabecular bone density (r = 0.37, p = 0.02). We conclude that micronized 17-beta-estradiol has a continuous skeletal dose-response effect in the range of 0.5 to 2.0 mg and that calcium intake positively modifies the skeletal response to 1.0 mg micronized 17-beta-estradiol.