Calcium accretion in girls and boys during puberty: A longitudinal analysis

The primary purpose of this study was to estimate the magnitude and variabi lity of peak calcium accretion rates in the skeletons of healthy white adol escents. Total-body bone mineral content (BMC) was measured annually on six occasions by dual-energy X-ray absorptiometry (DXA; Hologic 2000, array mo de), a BMC velocity curve was generated for each child by a cubic spline fi t, and peak accretion rates were determined. Anthropometric measures were c ollected every 6 months and a 24-h dietary recall was recorded two to three times per year. Of the 113 boys and 115 girls initially enrolled in the st udy, 60 boys and 53 girls who had peak height velocity (PHV) and peak BMC v elocity values were used in this longitudinal analysis. When the individual BR IC velocity curves were aligned on the age of peak bone mineral velocit y, the resulting mean peak bone mineral accrual rate was 407 g/year for boy s (SD, 92 g/year; range, 226-651 g/year) and 322 g/year for girls (SD, 66 g /year; range, 194-520 g/year). Using 32.2% as the fraction of calcium in bo ne mineral, as determined by neutron activation analysis (Ellis et al., J B one Miner Res 1996;11:843-848), these corresponded to peak calcium accretio n rates of 359 mg/day for boys (81 mg/day; 199-574 mg/day) and 284 mg/day f or girls (58 mg/day; 171-459 mg/day). These longitudinal results are 27-34% higher than our previous cross-sectional analysis in which we reported mea n values of 282 mg/day for boys and 212 mg/day for girls (Martin et al., Am J Clin Nutr 1997;66:611-615). Mean age of peak calcium accretion was 14.0 years for the boys (1.0 years; 12.0-15.9 years), and 12.5 years for the gir ls (0.9 years; 10.5-14.6 years). Dietary calcium intake, determined as the mean of all assessments up to the age of peak accretion was 1140 mg/day (SD , 392 mg/day) for boys and 1113 mg/day (SD, 378 mg/day) for girls. We estim ate that 26% of adult calcium is laid down during the 2 adolescent years of peak skeletal growth. This period of rapid growth requires high accretion rates of calcium, achieved in part by increased retention efficiency of die tary calcium.