Calcium Intake May Protect Against Bone Loss During Moderate Weight Loss

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April 11, 2007 — Healthy, overweight, premenopausal women had no bone loss with moderate weight reduction if they consumed 1 or 1.8 g/day of calcium, according to the results of a study reported in the April issue of the American Journal of Clinical Nutrition.

"Weight loss is associated with bone loss, but this has not been examined in overweight premenopausal women," write Claudia S. Riedt, from Rutgers University in New Brunswick, New Jersey, and colleagues. "Compared with obese persons, overweight persons may be more susceptible to bone loss due to reduced weight bearing, diminished extraovarial estrogen synthesis due to smaller fat depots, and reduced calcium intake due to lower energy requirements, especially during dieting.... Our aims were to examine bone turnover and mass in overweight premenopausal women with weight reduction at recommended or high calcium intakes and to determine the role of calcium absorption and hormonal regulators."

In the current study, 44 overweight premenopausal women were randomized to either normal (1 g/day) or high (1.8 g/day) calcium intake during 6 months of energy restriction (weight loss groups) or were recruited for weight maintenance with calcium intake of 1 g/day. Mean age was 38 ± 6.4 years, and mean body mass index (BMI) was 27.7 ± 2.1 kg/m2.

Dual-energy x-ray absorptiometry measured regional bone mineral density (BMD) and content. A dual-stable calcium isotope method measured true fractional calcium absorption at baseline and during caloric restriction. Markers of bone turnover were measured before and after weight loss.

The weight loss groups lost 7.2% ± 3.3% of initial body weight. There was no significant decrease in BMD or rise in bone turnover with weight loss at normal or high calcium intake. In the group with high calcium intake, there was a strong correlation (r = 0.71) between increased femoral neck BMD and increased serum 25-hydroxyvitamin D. There was no significant effect of weight loss on true fractional calcium absorption, and the total calcium absorbed was adequate (238 ± 81 mg/day in the normal-calcium weight loss group, and 310 ± 91 mg/day in the high-calcium weight loss group).

Study limitations include concerns about the validity of dual-energy x-ray absorptiometry measurements in heavier people and in weight loss studies.

"We showed that dieting overweight premenopausal women do not lose bone with intakes of 1.0 or 1.8 g Ca/d, which may be explained by sufficient amounts of absorbed calcium," the authors conclude. "Furthermore, bone turnover was not up-regulated, and the calcium-PTH [parathyroid hormone] axis was not significantly increased because of weight loss. We suggest that overweight premenopausal women do not lose bone with moderate weight loss when consuming the recommended intake for calcium."

The National Institutes of Health supported this study. The authors have disclosed no relevant financial relationships.

Am J Clin Nutr. 2007;85:972-980.