DEVELOPMENT AND REGULATION OF CALCIUM-METABOLISM IN HEALTHY GIRLS

The major components of calcium metabolism, as evaluated by a dual-tra cer stable isotope method, were determined in 100 studies of 68 health y girls, aged 5-18 y and analyzed from a developmental and regulatory viewpoint. Bone calcium deposition and removal rates were closely corr elated with the size of the exchangeable bone calcium compartment. All three quantities, as well as intestinal calcium absorption, peaked at or near menarche. Both bone calcium deposition and removal rates were positively and linearly correlated with calcium absorption. However, in this correlation, because bone calcium deposition increased 70% fas ter than calcium absorption, most of the increase in the bone calcium compartment and its turnover must have occurred in response to somethi ng other than intestinal calcium input; presumably this occurred in re sponse to developmental signals. Nevertheless, the constancy of the se rum calcium in the face of a large intestinal calcium input and the mo dest way in which excretion overcame the calcium load in this populati on point to the importance of the exchangeable bone calcium compartmen t, in dynamic equilibrium with the bone mineral, as the site at which most of the load is taken up. In this population of girls, as in older women, this increase in the skeletal calcium balance resulted from a decrease in the bone calcium removal rate that was greater than the co rresponding increase in the bone calcium deposition rate.