Bone mineral contents and plasma osteocalcin concentrations of Gambian children 12 and 24 mo after the withdrawal of a calcium supplement

Background: Our randomized, placebo-controlled supplementation study of 160 rural Gambian children aged 8.3-11.9 y showed that an increase in calcium intake of 714 mg/d for 12 mo resulted in a 5% increase in forearm bone mineral acquisition and a 22% decrease in plasma osteocalcin concentration, a bone formation marker, but had no effect on height or bone dimensions. Objective: We investigated whether these results were sustained after supplement withdrawal. Design: All participants were followed up 12 (FU1) and 24 (FU2) mo after supplementation ended. Bone mineral content (BMC), bone mineral density (BMD), and BMC adjusted for bone width, body weight, and height (size-adjusted BMC) were measured at the midshaft and distal radius. Plasma osteocalcin concentration was measured at FU1. Results: At follow-up, the calcium group had greater bone mineral status than did the placebo group at the midshaft radius (mean difference +/- SE), FU1: BMC (4.7 +/- 1.6%; P = 0.004), BMD (5.1 +/- 1.1%; P less than or equal to 0.0001), size-adjusted BMC (5.0 +/- 1.1%; P less than or equal to 0.0001); FU2: BMC (3.8 +/- 1.6%; P = 0.02), BMD (2.7 +/- 1.3%; P less than or equal to 0.04), size-adjusted BMC (2.5 less than or equal to 1.3%; P = 0.06). Similar differentials were observed at the distal radius but were not significant. No significant differences in plasma osteocalcin concentrations (FU1: -0.5 +/- 6.5%; P = 0.9) were observed between groups. Conclusion: Although some of the effects of calcium supplementation were still evident at follow-up, further studies are required to determine whether short-term increases in calcium intake have lasting benefits for Gambian children.