PUBERTAL CHANGES IN CALCIUM KINETICS IN GIRLS ASSESSED USING CA-42

The rate of calcium deposition in bone (V(o)+) and the size of the exchangeable calcium pool in bone (EP) were measured in 50 girls aged 4.9 to 16.7 y using i.v. administered Ca-45. Both V(o)+ and EP reached a maximum during early puberty and decreased in late puberty and more than 2 y postmenarche. In contrast, the initial mass of calcium distribution did not decrease in late puberty. The ratio of calcium deposition in bone to the exchangeable pool size, i.e. k(o)+ = V(o)+/EP, was more closely correlated with length of time since menarche (r = 0.83, p < 0.001) than with age (r = 0.65, p < 0.001), weight (r = 0.51, p < 0.001), or body mass index (r = 0.28, p = 0.05). The lower k(o)+ in late puberty indicates that as bone matures the fraction of the calcium pool that enters bone decreases.