Net calcium absorption in premature infants: Results of 103 metabolic balance studies

Abstract

Net calcium absorption was evaluated in 103 low-birth-weight preterm infants by a 72-h balance technique. At birth the infants had a mean (± SE) gestational age of 30.9 ± 0.2 wk and weighed 1.43 ± 0.03 kg. When tested 3 wk later, their net calcium absorption averaged 58 ± 1% with an intake of 80 ± 2 mg Ca·kg body wt-1·d-1. Of the 103 infants, 58 had been fed low-birth-weight formulas supplemented with vitamin D. The remainder received banked human milk, of whom 34 were supplemented with vitamin D and calcium; 11 infants received no supplementation. Calcium absorption in the four subgroups did not differ significantly, with neither vitamin D supplementation nor supplementation with vitamin D and calcium affecting percent absorption significantly. Net calcium absorption was a linear function of intake (40-130 mg Ca·kg body wt-1·d-1) with a zero intercept. Because vitamin D supplementation did not increase net calcium absorption, it is concluded that in preterm low-birth-weight infants calcium absorption proceeds by a nonsaturable route, with the transcellular, vitamin D-regulated mechanism not yet expressed.