Source: Am J Clin Nutr, February 2008;87(2):455-462.
Research: A recent meta-analysis raised doubt as to whether calcium supplementation in children benefits spine and hip bone mineral density (BMD). In this study, researchers used measures of bone (fan-beam dual-energy X-ray absorptiometry and 4 bone turnover markers) to determine whether girls with low habitual calcium intake benefited from supplementation with a soluble form of calcium (calcium citrate malate dissolved in a fruit drink). The trial was an 18-month randomized trial of calcium supplementation (792 mg/d) with two years of follow-up after supplement withdrawal. Ninety-six girls (mean age: 12 years) with low calcium intakes (mean: 636 mg/d) participated in the study. The main outcome measure was change in total-body, lumbar spine and total hip bone mineral content (BMC) during supplementation and 2 years after supplement withdrawal. Changes in BMD and bone turnover markers were secondary outcome measures.
Results: The mean additional calcium intake in the supplemented group was 555 mg per day. Compared with the control group, the supplemented group showed significantly greater gains in BMC (except at the total hip site) over the 18-month study. BMD change was significantly greater for all skeletal sites, and concentrations of bone resorption markers and parathyroid hormone were significantly lower in the supplemented group than in the control group after 18 months. After 42 months, gains in BMC and BMD and differences in bone resorption were no longer evident. Researchers concluded that calcium supplementation enhances bone mineral accrual in teenage girls, but the effect is short-lived. The likely mechanism for the effect of the calcium is suppression of bone turnover, which is reversed upon supplement withdrawal.