Bone turnover and density in obese premenopausal women during moderate weight loss and calcium supplementation.

Bone turnover is increased during weight loss in postmenopausal women and can be suppressed with calcium supplementation. In this study, we assessed the influence of energy restriction with and without calcium supplementation (1 g/day) in premenopausal women. Thirty-eight obese premenopausal women (body mass index [BMI] of 35.0 +/- 3.9 kg/m2) completed a 6-month study of either moderate weight loss or weight maintenance. During weight loss, women were randomly assigned to either a calcium supplementation (n = 14) or placebo group (n = 14) and lost 7.5 +/- 2.5% of their body weight. The control group of women (n = 10) maintained their body weight. Total body and lumbar bone mineral density (LBMD) and content were measured by dual-energy X-ray absorptiometry (DXA) at baseline and after weight loss. Throughout the study, blood and urine samples were collected to measure bone turnover markers and hormones. During moderate energy restriction, dietary calcium intake decreased (p < 0.05) and the bone resorption marker deoxypyridinoline (DPD) increased slightly (p < or = 0.05) without evidence of bone loss. Calcium supplementation during weight loss tended to increase lumbar BMD by 1.7% (p = 0.05) compared with the placebo or weight maintenance groups. In contrast to our previous findings in postmenopausal women, premenopausal obese women who consume a low calcium diet do not lose bone over a 6-month period, whether their weight is stable or decreasing moderately.

Moderate energy restriction increases bone resorption in obese postmenopausal women.

BACKGROUND: Weight reduction reduces bone mineral density (BMD) and increases the risk of osteoporosis. OBJECTIVE: We investigated whether bone is mobilized in postmenopausal women during energy restriction and whether hormones regulate bone turnover and mass. DESIGN: Twenty-seven obese postmenopausal women with a mean (+/-SD) age of 55.9 +/- 7.9 y and body mass index (in kg/m(2)) of 33.0 +/- 3.8 completed the 6-mo study. Fourteen women followed a moderate energy-restricted diet (WL group) and 13 control subjects maintained their body weight (WM group). Body weight, bone turnover markers, serum parathyroid hormone (PTH), and dietary intake were measured throughout the study. Total-body BMD, sex hormone binding globulin, leptin, and estrone were measured at baseline and at week 25. RESULTS: In the WL group, body weight decreased by 10.2 +/- 5.5% (P < 0.001), body fat mass decreased by 18.7 +/- 11.3% (P < 0.001), and total-body BMD decreased by 1.2 +/- 1.2%; these changes were significantly different from those in the WM group (P < 0.05). Serial measurements showed chronically elevated rates of bone resorption and formation during energy restriction that were greater than in the WM group (P < 0.05). Serum sex hormone binding globulin increased and leptin decreased with weight loss (P < 0.05). Serum PTH tended to increase in the WL group but not in the WM group (P < 0.06). The reduction in fat mass with weight loss was directly associated with a decrease in serum estrone (P < 0.01, R(2) = 0.50). CONCLUSIONS: Moderate energy restriction increases bone turnover in obese postmenopausal women and may be regulated in part by alterations in serum PTH and estrone.

Calcium supplementation suppresses bone turnover during weight reduction in postmenopausal women.

Bone mobilization, lowering of bone mineral density (BMD), and osteoporotic fractures are recognized in postmenopausal women with weight loss. Because a high-calcium intake suppresses bone loss in peri- and postmenopausal women, the present randomized, double-blind, placebo-controlled study was designed to test the hypothesis that calcium supplementation prevents net bone mobilization and consequent bone mineral loss during voluntary weight reduction in obese postmenopausal women. Subjects were placed on a moderate energy-restricted diet and either calcium supplementation (1 g/day) or placebo for 6 months. Body weight, bone turnover markers (pyridinium cross-links), osteocalcin, and parathyroid hormone (PTH) were measured at treatment weeks 1-5, 7, 10, 13, 16, 20, and 25. Total body BMD, insulin-like growth factor, 25-hydroxyvitamin D, and sex hormone binding globulin (SHBG) were measured at baseline and week 25. The calcium supplemented (n = 15; age 60.9 +/- 9.4 years, body mass index [BMI] 33.2 +/- 4.6 kg/m2) and placebo (n = 16; age 55.8 +/- 8.3 years, BMI 32.9 +/- 4.5 kg/m2) groups lost similar amounts 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 statistical effect of calcium supplementation during weight loss to suppress pyridinium cross-links, osteocalcin, and PTH (p < 0.05, < 0.01, and < 0.05, respectively). Loss of BMD tended to be greater in the placebo group by 1.4% (p < 0.08) after weight loss. One gram per day calcium supplementation normalizes the increased calcium-PTH axis activity and the elevated bone turnover rate observed during moderate voluntary energy restriction in postmenopausal women.