DEVELOPMENTAL-CHANGES IN CALCIUM KINETICS IN CHILDREN ASSESSED USING STABLE ISOTOPES

Total exchangeable calcium pool size (TEP) and bone calcium accretion rate (V(o)+) were measured using stable isotopes in healthy children and young adults. Ca-42 or Ca-46 was given intravenously to 10 children aged 10 months to 14 years and 3 women aged 23-33 years. Calcium kinetic parameters were determined using a two- or three-exponential curve of the resultant serum and urine tracer excesses. These data were compared with previously reported (radiotracer) kinetic studies of 21 children and 5 adults without known bone disease. Current results are comparable to those previously obtained, and the data from all studies were analyzed together. Total V(o)+ was significantly greater in children aged 3-16 years than in adults (2.8 +/- 1.6 versus 0.7 +/- 0.2 g/day, p < 0.01). Both TEP and V(o)+ were significantly correlated to age independently of variations in body weight (p < 0.01 for each). The ratio k(o)+ = V(o)+/TEP was greater in children than adults (0.36 +/- 0.15 versus 0.12 +/- 0.03 day-1, p < 0.001). These data demonstrate increased bone flow of calcium associated with increases in exchangeable calcium pools in children compared to adults. V(o)+ and TEP may be maximum in early adolescence, associated with peak rates of net calcium accretion. The use of stable isotopes permits the safe evaluation of calcium kinetics in patients of all ages.