Calcium supplementation and bone mineral accretion in adolescent girls: an 18-mo randomized controlled trial with 2-y follow-up1-3
A recent meta-analysis raised doubt as to whether calcium supplementation in children benefits spine and hip bone mineral density (BMD).Objective:
We used state-of-the-art 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).Design:
The trial was an 18-mo randomized trial of calcium supplementation (792 mg/d) with follow-up 2 y after supplement withdrawal. Subjects were 96 girls (mean age: 12 y) with low calcium intakes (mean: 636 mg/d). The main outcome measure was change in total-body, lumbar spine, and total hip bone mineral content (BMC) during supplementation and 2 y 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/d. Compared with the control group, the supplemented group showed significantly (P < 0.05) greater gains in BMC (except at the total hip site) over the 18-mo study. BMD change was significantly (P < 0.05) greater for all skeletal sites, and concentrations of bone resorption markers and parathyroid hormone were significantly (P < 0.01) lower in the supplemented group than in the control group after 18 mo. After 42 mo, gains in BMC and BMD and differences in bone resorption were no longer evident.Conclusions:
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.