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Measurement of true absorption, endogenous fecal excretion, urinary excretion, and retention of calcium in term infants by using a dual-tracer, stable-isotope method



Measurement of true absorption, endogenous fecal excretion, urinary excretion, and retention of calcium in term infants by using a dual-tracer, stable-isotope method



Journal of Pediatrics 123(3): 444-456



A dual-tracer, stable-isotope method was used to measure the percentage of true calcium absorption (alpha), true calcium absorption rate (V-alpha), endogenous fecal calcium excretion rate (V-f), urinary calcium excretion rate (V-u), and calcium retention rate (V-r). Twenty-seven infants with a mean gestation of 30.6 +- 1.7 weeks and a mean birth weight of 1.4 +- 0.21 kg were studied at 2 or 3 weeks of age, or both, during feedings of human milk (HM), fortified human milk (HMF), and commercially available formula (20 or 24 calories per ounce) for premature infants (EPF-20/780 and EPF-24/940) (part 1 of our study). Of 13 additional infants with a mean (+- SD) birth weight of 1.26 +- 0.25 kg and gestation of 29.6 +- 2.5 weeks, 11 completed a crossover-design study at 2 and 3 weeks of age, receiving two identical formulas containing calcium, 940 mg/L, and phosphorus, 470 mg/L (EPF-24/940 formula) or calcium 1340 mg/L, and phosphorus, 680 mg/L (EPF-24/1340 formula) (part 2 of our study). The alpha value was higher in infants receiving HM (76.4 +- 15.1%) r HMF (68.0 +- 7.8%) than in those receiving EPF-20/750 formula (54.1% +- 5.6%) or in previously reported infants fed standard formula (47.1% +- 11.5%); those given EPF-24/940 formula had intermediate values (63.9% +- 13.9%, part 1; 56.1% +- 16.5%, part 2). No significant differences existed among groups for either V-u or V-f per kilogram. In the crossover study (part 2), no significant differences were seen between formulas for alpha and for V-alpha, V-f, or V-r per kilogram. However, V-u per kilogram was significantly decreased in infants receiving the higher mineral formula (EPF-24/940: 3.6 +- 2.3; EPF-24/1340: 2.9 +- 2.3 mg/kg per day; p = lt 0.005). With all feedings, alpha, V-u per kilogram, and V-f per kilogram were not related to gestational age, age at study, calcium intake, or each other. However, V-f per kilogram was inversely related to birth weight. Thus, alpha, V-u, and V-f appear to be independent and may be differentially affected by factors altering calcium dynamics. We conclude that increasing formula mineral content does not ensure increased retention; careful monitoring of individual infants remains indicated.

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Accession: 002429739

Download citation: RISBibTeXText

PMID: 8355125

DOI: 10.1016/s0022-3476(05)81755-x


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