Zinc and copper balances in preterm infants

Preterm infants are at risk for copper and zinc depletion if sufficient quantities of these nutrients are not provided in a bioavailable form in postnatal life. The purpose of this study was to determine whether the use of a whey-predominant, 50% medium chain triglyceride formula with relatively high concentrations of zinc and copper would promote the achievement of the in utero accretion rate for zinc and copper in the preterm infant. Two groups of five preterm infants were fed a diet containing 12.5 mg/L of zinc and either 0.9 mg/L or 2.1 mg/L of copper. Seventy-two-hour metabolic balance studies were performed at an average postconceptual age of 34 weeks and an average weight of 1,549 g. All infants were in positive zinc balance and nine of ten achieved the in utero accretion rate for zinc for a 34-week gestation fetus (greater than or equal to 0.432 mg/d). Three infants receiving the high copper formula and two receiving the lower copper formula were in positive copper balance. Two infants from each group achieved the in utero accretion rate for copper for a 34-week gestation fetus (0.088 mg/d). A formula that provides 12.5 mg/L of zinc permits positive zinc balance and zinc retention similar to in utero rates. A formula that provides as much as 2.1 mg/L of copper, however, may not always permit positive copper balance.