A Cochrane review included 19 studies with a total of 2 859 subjects. There was no effect of calcium supplementation on femoral neck or lumbar spine bone mineral density (BMD). There was a small effect on total body bone mineral content (BMC) (standardised mean difference SMD +0.14, 95% CI+0.01, +0.27) and upper limb BMD (SMD +0.14, 95%CI +0.04, +0.24). Only the effect in the upper limb persisted after supplementation ceased (SMD+0.14, 95%CI+0.01, +0.28). This effect is approximately equivalent to a 1.7% greater increase in supplemented groups, which at best would reduce absolute fracture risk in children by 0.1–0.2%per annum.