Effects of calcium supplementation on bone density in healthy children: meta-analysis of randomised controlled trials

Systematic review and meta-analysis of 19 randomized controlled trials in healthy children and adolescents younger than 18 years. Across the active calcium arms, 1367 participants were randomized to calcium and 1426 to placebo, with baseline pubertal stage, sex, ethnicity, and calcium intake varying across studies.

Calcium supplementation, delivered in varied forms across trials including calcium carbonate, calcium citrate malate, calcium phosphate, milk extract, and milk-mineral fortified foods, was given at doses ranging from 300 mg/day to 1200 mg/day for about 0.7 to 7 years. The active calcium regimens were compared with placebo in healthy children and adolescents.

Calcium supplementation had little overall effect on bone mineral density in healthy children. There was no significant benefit at the femoral neck (0.07, -0.05 to 0.19) or lumbar spine (0.08, -0.04 to 0.20), while small positive effects were seen for total body bone density at the end of supplementation (0.14, 0.01 to 0.27) and upper limb bone density (0.14, 0.04 to 0.24). After supplementation stopped, the total body effect disappeared (0.00, -0.40 to 0.40), although a small upper-limb effect remained (0.14, 0.01 to 0.28). There was no evidence that sex, baseline calcium intake, pubertal stage, ethnicity, or physical activity modified the effect, and reported adverse events were infrequent and minor.

Trials used different calcium forms, doses, durations, and bone sites, which increases heterogeneity and limits direct comparability. The observed effects were small and site-specific, fracture outcomes were not established, and follow-up after stopping supplementation was limited. Adverse event reporting was sparse, and sensitivity analyses depended in part on imputed data.