CALCIUM SUPPLEMENTATION SUPPRESSES BONE TURNOVER DURING WEIGHT-REDUCTION IN POSTMENOPAUSAL WOMEN

Bone mobilization, lowering of bone mineral density (BMD), and osteopo rotic fractures are recognized in postmenopausal women with weight los s. Because a high-calcium intake suppresses bone loss in peri-and post menopausal women, the present randomized, double-blind, placebo-contro lled study was designed to test the hypothesis that calcium supplement ation prevents net bone mobilization and consequent bone mineral loss during voluntary weight reduction in obese postmenopausal women. Subje cts were placed on a moderate energy-restricted diet and either calciu m supplementation (1 g/day) or placebo for 6 months. Body weight, bone turnover markers (pyridinium cross-links), osteocalcin, and parathyro id hormone (PTH) were measured at treatment weeks 1-5, 7, 10, 13, 16, 20, and 25. Total body BMD, insulin-like growth factor, 25-hydroxyvita min D, and sex hormone binding globulin (SHBG) were measured at baseli ne and week 25. The calcium supplemented (n = 15; age 60.9 +/- 9.4 yea rs, body mass index [BMT] 33.2 +/- 4.6 kg/m(2)) and placebo (n = 16; a ge 55.8 +/- 8.3 years, BMI 32.9 +/- 4.5 kg/m(2)) groups lost similar a mounts of weight over the study interval (10.2 +/- 5.3% vs. 10.0 +/- 5 .2%) and both groups increased SHBG (p < 0.001). There was a statistic al effect of calcium supplementation during weight loss to suppress py ridinium cross-links, osteocalcin, and PTH (p < 0.05, < 0.01, and < 0. 05, respectively). Loss of BMD tended to be greater in the placebo gro up by 1.4% (p < 0.08) after weight loss. One gram per day calcium supp lementation normalizes the increased calcium-PTH axis activity and the elevated bone turnover rate observed during moderate voluntary energy restriction in postmenopausal women.