Differences in calcium kinetics between adolescent girls and young
women.
Wastney, Me, J Ng, D Smith, Br Martin, M Peacock, and Cm Weaver.
Georgetown University Medical Center, 3800 Reservoir Rd., N.W.
Washington, DC 20007, Purdue University, W. Lafayette, IN 47907, IU
School of Medicine, Indianapolis, IN 46226
APStracts 3:0060R, 1996.
Rapid bone accretion occurs throughout childhood but peaks during
adolescence. The achievement of optimal peak bone mass, which can
protect against osteoporosis later in life, is greatly dependent on
rates of bone accretion. To identify differences in calcium
metabolism during rapid vs. slower bone accretion, calcium kinetics
were compared in 14 healthy girls aged 11-14 yr and 11 women aged 19
-31 yr. Calcium kinetics were measured while subjects were undergoing
a calcium balance study in a camp simulating a free-living
environment. After 7 days on a diet containing 1330 mg Ca/d, two
stable isotopes were administered (44Ca orally and 42Ca
intravenously) and blood samples, and all urine and feces were
collected for 14 days. Samples were analyzed for total calcium by
atomic absorption spectrophotometry and for enrichment of 42Ca and
44Ca by fast atom bombardment mass spectrometry. Data from serum,
urine and feces were analyzed using the Simulation, Analysis And
Modeling (SAAM) software. Data were fitted by a 3-compartment model;
the first pool was the same size in girls and women (1.6 g) but the
second and third pools were larger in girls (2.85 vs 1.66 g and 12 vs
5 g). Compared to the women, girls absorbed more calcium from the
diet (38 vs 22% or 494 vs 283 mg/d), excreted less calcium in urine
(100 vs 203 mg/d), deposited more calcium in bone (1459 vs 501 mg/d)
and resorbed more calcium from the skeleton (1177 vs 542 mg/d) while
endogenous calcium excretion did not differ between girls and women
(112 vs 121 mg/d). Girls retained more calcium than women (282 vs -41
mg/d) through increased absorption, lower urine excretion, and higher
bone turnover.
Received 7 June 1995; accepted in final form 14 February 1996.
APS Manuscript Number R344-5.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 13 March 96