Zinc balance in premature infants given the minimal dietary zinc requirement.

A zinc balance study was conducted on low birth weight infants (670 to 2420 g) fed unsupplemented human milk (the mother's or pooled) (group 1, n = 17) or human milk with zinc supplementation (group 2, n = 17). The mean zinc concentrations of the diets in groups 1 and 2 were 2.2 +/- 1.1 mg/L and 8.4 +/- 0.8 mg/L, respectively, and the mean copper concentration of the diets in both groups was 0.45 +/- 0.12 mg/L. The studies were performed 7 to 128 days after birth, which corresponded to 29 to 43 weeks postconceptional age. The turning point of zinc balance from negative to positive appeared to be greatly influenced by the postconceptional age, being approximately 36 weeks in both group 1 and group 2, rather than other factors such as the zinc intake and the postnatal age. The calculated minimal requirement of dietary zinc during the period from 36 to 40 weeks postconceptional age, for an adequate amount of zinc retention in infants (250 micrograms/kg/d), was 0.8 mg/kg/d. Zinc supplementation did not appear to interfere with copper retention.