Changes in Calcium Kinetics in Adolescent Girls Induced by High Calcium Intake¹

Abstract

To identify the mechanism/s whereby calcium retention is increased by calcium intake in adolescent girls, kinetic studies were performed using stable calcium isotope tracers. Girls (n ϭ 10; 12 Ϯ 1 yr old, mean Ϯ SD) were studied while on a controlled diet containing a low (21.2 mmol/day) and a high (47.4 mmol/day) calcium intake, in randomized order, using a cross-over design. Studies were separated by 1 month. Calcium tracers were administered after 1 week on the study diet, orally and iv; and serum, urine, and feces were collected for the following 14 days. Tracers were measured using fast atom bombardment mass spectrometry, and kinetic data were analyzed by compartmental modeling. Biochemical markers of bone turnover were measured in serum and urine samples. On high (compared with low) calcium intake, fractional absorption did not differ, absorbed calcium increased (19.6 Ϯ 7.5 vs. 8.0 Ϯ 2.5 mmol/day, mean Ϯ SD, P Ͻ 0.001), calcium excreted in urine increased (2.8 Ϯ 1.7 vs. 2.1 Ϯ 1.1 mmol/day, P Ͻ 0.01), calcium retained in bone increased (14.5 Ϯ 8.9 vs. 3.2 Ϯ 3.6 mmol/ day, P Ͻ 0.001), bone formation did not change, and bone resorption decreased by 32%. These changes, measured by kinetics, were corroborated by changes in markers of bone turnover. We conclude that increased bone retention of calcium, with high calcium intake in adolescent girls, is attributable to an increase in absorption and a decrease in bone resorption. (J Clin Endocrinol Metab 85: 4470 -4475, 2000)

Dietary calcium utilization among a group of spanish boys aged 11–14 years on their usual diets

“…Thus, in normal children in mid-puberty, a relatively high calcium retention is needed to obtain an average bone mineralization, and the calcium intake must allow the body to be in sufficient positive balance to meet bone demands for growth. In the present assay, however, daily calcium retention was lower than that described for the whole period of adolescence (210 mg/day) (8), although the fractional retention (19%) was similar to that found in other studies of adolescents (29,1).…”

“…The faecal calcium excretion (69% of the intake) leads to a fractional calcium absorption lower than 41% found in adolescent girls with high calcium intake (1896 mg/day) (29), but higher than that for boys aged 9-14 years (27.4 %) consuming a calcium diet of 1300 mg/d (1). The relatively high fractional calcium absorption may be attributed to the consumption of dairy products as the major source of dietary calcium, since the calcium in milk products is highly available (10).…”

“…Adolescents retain more calcium than adults through increased absorption and suppression of bone resorption (29). Average increments of body calcium during adolescence are 210 mg/d, but at the peak of growth daily calcium deposition is approximately twice (8).…”

Labeling the human skeleton with 41Ca to assess changes in bone calcium metabolism

“…Furthermore, the residual plots and the variability estimates were comparable between both models, with model 2 a sequential model and model 3 a Y-type model. Many recent models [35][36][37] use a series model, although various authors [25,38] have pointed out the equivalence of the various branching schemes, concluding that the choice of model architecture is ultimately heuristic.…”

Use of Calcium Isotopic Tracers To Determine Factors That Perturb Calcium Metabolism

“…To suppress the bone resorption induced by obligatory daily losses of calcium, dietary calcium must be provided daily. Calcium insufficiency decreases bone mass and increases osteoporotic fracture risk, while increasing calcium intake suppresses bone resorption and increases bone accrual. − …”