Effects of milk salt supplementation on bone mineral gain in pubertal Chinese adolescents: a 2-year randomized, double-blind, controlled, dose-response trial.

ABSTRACT

BACKGROUND/OBJECTIVE: Adequate calcium intakes may enhance bone mineral accumulation during childhood. Little is known about the optimal calcium intake in Chinese adolescents. We examined the effects of three levels of calcium intake on bone mineral accretion in adolescents. METHODS: This was a 2-year randomized, double-blind, controlled trial. The subjects were randomly assigned to receive 40 g of milk powder containing 300 mg of calcium and 200 IU of vitamin D (Low-Ca group), or same milk powder additionally fortified with 300 mg of calcium (Mid-Ca group) or 600 mg of calcium (High-Ca group) for 2 years. The subjects' bone mineral density (BMD) and bone mineral content (BMC) at the total body, lumbar spine and left hip were determined by dual-energy X-ray absorptiometry at baseline and after the second year of treatment. Of the 111 girls and 109 boys (aged 12-14 years) enrolled, 91 girls and 91 boys completed the trial. RESULTS: The girls in the High-Ca group (1,110 mg/d) had 2.3%, 2.7% and 2.6% greater BMD accretion at the total hip, femoral neck and shaft (P<0.05) but not at total body less head and spine than those in the Low-Ca group (655 mg/d). A significant effect of higher calcium intake was also observed for percentage change of size-adjusted BMC at femur neck (P=0.047). Bonferroni tests indicated no significant differences in the percentage changes in BMD, BMC or size-adjusted BMC between the Mid- and Low-Ca groups and between the High- and Mid-Ca groups. Extra calcium had no observable additional effect in the boys (P>0.05). CONCLUSION: An intake of 1000 mg/d or more might be helpful in maximizing bone mineral accretion in the hip for girls. But further large studies are required to identify its long-term effects and the optimal calcium intake for boys.