Bone mass and density response to a 12-month trial of calcium and vitamin D supplement in preadolescent girls.

BACKGROUND: Maximal bone acquisition in adolescent girls through dietary and lifestyle practices is advocated to prevent or minimize the development of osteoporosis and its associated complications in later life. Longitudinal investigations of bone acquisition in children and adolescents have utilized areal bone mineral density (BMD, mg/cm(2)) as a measure of bone mass and strength. Peripheral quantitative computed tomography (pQCT), which provides a three-dimensional display of data, separate analyses of bone compartments, and bone mass in terms of volumetric BMD (vBMD, mg/cm(3)), has recently been introduced for clinical use.

OBJECTIVE: To assess the impact of a 12-month daily calcium supplement on total and trabecular bone acquisition as measured by pQCT in preadolescent girls.

DESIGN: Early adolescent Caucasian girls (aged 12 years, Tanner Stage 2) were enrolled in a randomized trial of daily calcium supplement (TX, 800 mg calcium carbonate and 400 IU vitamin D) or placebo (C). Body weight, height, and distal tibia measurements by pQCT were obtained at enrollment, 6 and 12 months. Pubertal status and physical activity records were assessed at baseline and 12 months. Three-day food intake records were completed every three months.

RESULTS: Seventy-one girls completed the 12-month trial (TX=35, C=36). No differences were found for age, weight, height, body mass index, pubertal maturation, or reported physical activity at enrollment or during the study. Average intakes during the study were 1524 mg calcium and 496 IU vitamin D (TX) versus 865 mg calcium and 160 IU vitamin D (C) per day. Baseline total bone values were similar, however, trabecular values were greater in TX girls despite randomization. Percent changes were calculated to adjust for baseline differences. Because of the small cortical thickness at the 10% site (mean values < 1.6 mm), cortical mass and density were not analyzed. The percent changes for trabecular bone mineral content (BMC, mg) and vBMD were significantly greater in TX girls (+4.1% BMC and +1.0% vBMD TX versus -1.6% BMC and -2.0% vBMD C, p<0.006; ANCOVA) after 12 months of supplement. Trabecular bone area (BA, cm(2)) and total bone change, however, did not differ between groups.

CONCLUSIONS: Daily calcium and vitamin D supplementation promotes greater trabecular BMC and vBMD acquisition in preadolescent girls. The single site selected for pQCT evaluation in this study did not allow evaluation of the cortical bone compartment. Future studies that utilize the pQCT technique need to incorporate multiple measurement sites to better assess total, cortical, and trabecular bone.