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Compartmental analysis of calcium metabolism in very-low-birth-weight infants
S A Abrams1, R J Schanler, A L Yergey
1Department of Pediatrics, Children's Nutrition Research Center, Houston, TX 77030.
Insights
Very-low-birth-weight infants exhibit higher bone calcium deposition rates than adults, crucial for rapid growth. Their calcium metabolism is highly responsive to absorption, unlike in older individuals.
Area of Science:
- Neonatal Physiology
- Calcium Metabolism
- Pediatric Nutrition
Background:
- Infant bone development requires precise calcium regulation.
- Understanding calcium metabolism in premature infants is critical for growth.
- Previous studies lacked detailed kinetic data on calcium handling in VLBW infants.
Purpose of the Study:
- To evaluate calcium metabolism in very-low-birth-weight (VLBW) infants.
- To quantify bone calcium deposition and removal rates.
- To correlate calcium absorption with deposition and removal.
Main Methods:
- Stable isotope kinetic and balance studies were performed.
- Orally and intravenously administered stable isotopes were utilized.
- A sequential, three-compartment model analyzed kinetic data.
Main Results:
- VLBW infants showed significantly higher bone calcium deposition rates (160 mg/kg/day).
- Bone calcium deposition increased markedly with net calcium absorption (r=0.70, p<0.01).
- Bone calcium removal showed a smaller response to absorption in infants compared to adults.
Conclusions:
- VLBW infants' high bone calcium deposition supports rapid growth, typical of late gestation.
- Calcium metabolism in these infants is highly sensitive to absorption levels.
- Findings highlight unique physiological adaptations for bone mineralization in premature neonates.
Abstract:
The calcium metabolism of 13 very-low-birth-weight infants fed a high-calcium diet was evaluated by means of stable isotope kinetic and balance studies. The studies used orally and i.v. administered stable isotopes, and the kinetic data were evaluated with the aid of a sequential, three-compartment model. The infants (postmenstrual age 33 +/- 1 wk, weight 1.34 +/- 0.03 kg) had higher bone calcium deposition rates (160 +/- 7 mg.kg-1.d-1 or 4.00 +/- 0.18 mmol.kg-1.d-1) than those previously reported for either older children or adults. Furthermore, when analyzed as a function of net calcium absorption, bone calcium deposition rates increased markedly and significantly as net calcium absorption increased (r = 0.70, p < 0.01), whereas in older individuals, bone calcium deposition is a relatively invariant function of absorption. A relatively smaller response of bone calcium removal to calcium absorption was found for the very-low-birth-weight infants in this study (r = -0.39, p = 0.18), whereas in adults, bone calcium removal constitutes the major regulatory response. It is suggested that the calcium kinetic results in the very-low-birth-weight infants reflect the high rate of bone growth typical of the third trimester of gestation.