Premenopausal overweight women do not lose bone during moderate weight loss with adequate or higher calcium intake

Abstract

Background: Weight loss is associated with bone loss, but this has not been examined in overweight premenopausal women.

Objective: The aim of this study was to assess whether overweight premenopausal women lose bone with moderate weight loss at recommended or higher than recommended calcium intakes.

Design: Overweight premenopausal women [n = 44; x (+/-SD) age: 38 +/- 6.4 y; body mass index (BMI): 27.7 +/- 2.1 kg/m(2)] were randomly assigned to either a normal (1 g/d) or high (1.8 g/d) calcium intake during 6 mo of energy restriction [weight loss (WL) groups] or were recruited for weight maintenance at 1 g Ca/d intake. Regional bone mineral density and content were measured by dual-energy X-ray absorptiometry, and markers of bone turnover were measured before and after weight loss. True fractional calcium absorption (TFCA) was measured at baseline and during caloric restriction by using a dual-stable calcium isotope method.

Results: The WL groups lost 7.2 +/- 3.3% of initial body weight. No significant decrease in BMD or rise in bone turnover was observed with weight loss at normal or high calcium intake. The group that consumed high calcium showed a strong relation (r = 0.71) between increased femoral neck bone mineral density and increased serum 25-hydroxyvitamin D. No significant effect of weight loss on TFCA was observed, and the total calcium absorbed was adequate at 238 +/- 81 and 310 +/- 91 mg/d for the normal- and high-calcium WL groups, respectively.

Conclusion: Overweight premenopausal women do not lose bone during weight loss at the recommended calcium intake, which may be explained by sufficient amounts of absorbed calcium.

FIGURE 1

Flow diagram of participants in study. Failure to lose weight was defined as weight loss of <2.5% of initial body weight. Low compliance was defined as those who took <60% of the calcium supplement. HiCa, high calcium; NLCa, normal calcium; WL, weight loss; WM, weight maintenance.

FIGURE 2

Relation between changes in serum 25-hydroxyvitamin D [25(OH)D] or parathyroid hormone (PTH) and femoral neck bone mineral density (FN BMD) in the weight loss high calcium (WL HiCa) and the WL normal calcium (NLCa) groups. The relation between 25(OH)D and FN BMD was significant (r=0.705, P<0.005) for the WL HiCa group, but not for the WL NLCa group (r = −0.232, P = NS). A trend (P < 0.06) for a difference in the slopes between the groups was observed. Changes in PTH and FN BMD were observed only in the WL Hi-Ca group (WL HiCa: r = −0.681, P < 0.01; and WL NLCa: r = 0.187, P = NS) without significant differences between the slopes after 6 mo of weight loss. ■ and solid line, WL HiCa group (n = 14), ◇ and dashed line, WL NLCa group (n = 17). Stepwise regression analysis was done with percentage change in BMD as the dependent variable, and independent variables included percentage change in weight, PTH, 25(OH)D, estradiol, and cortisol.