Zinc supplementation and plasma concentration of vitamin A in preterm infants.

To assess the effect of zinc supplementation on plasma retinol levels, 24 preterm infants were randomly assigned to receive 400 micrograms.kg-1.d-1 of intravenous Zn or no Zn supplementation. Intakes of protein, energy, and vitamin A were similar for both groups as were day 0 plasma concentrations of retinol, retinol-binding protein (RBP), and Zn. Zn concentrations were not significantly different between groups at any time during the 3-wk study; however, retinol values in wk 1 increased more in the supplemented group (delta = 10.0 vs 0.9 micrograms/dL, or 0.35 vs 0.031 mumol/L; p less than 0.005). RBP appeared to increase more in the supplemented group but did not reach statistical significance. We hypothesize that the increase in plasma retinol levels noted in the preterm infants receiving Zn supplementation may be mediated by an increased production of RBP in the liver that in turn enhances the hepatic release of retinol.