Postnatal dependence of plasma copper and zinc levels on gestational age and maturity observed in infants fed a high zinc content formula

Extract: We studied the effect of gestational age and maturity on plasma zinc and copper levels at 10 and 120 days of age. The association of plasma zinc changes and body growth was also investigated. Infants were receiving a controlled intake of zinc and copper solely through a zinc-supplemented formula (4.7 mg/L of zinc and 0.16 mg/L of copper). Twenty-eight low-birthweight infants (less than 2.500 g) having gestational ages ranging from 33 to 40 weeks [17 with an appropriate birthweight for gestational age (AGA) and 11 small for gestational age (SGA)] were enrolled in the present study. Measurements of plasma zinc and copper concentration, weight, length, head circumference, and tricipital and subscapular skinfolds were carried out at 10 and 120 days of age. Protein-induced x-ray fluorescence technique (PIXE) was used to assess copper and zinc concentrations. At 10 days of age a significant correlation between copper concentration and gestational age was found. At 120 days of age the copper concentration was higher than at 10 days and independent of gestational age and maturity (mean plus or minus SEM = 116 plus or minus 5 micrograms/dl). At 10 days of age no significant correlation between zinc content and gestational age was found (86 plus or minus 4 micrograms/dl). The plasma zinc percent change over the period from 10 to 120 days of age was positively correlated with gestational age in the whole sample as well as in AGA and SGA infants separately. The value of gestational age at which the zinc percent change turns from negative to positive was 35.6 plus or minus 0.7 weeks for AGA, 37.4 plus or minus 0.5 weeks for SGA, and 36.2 plus or minus 0.5 weeks for the whole sample. No significant correlation between the increments of the measured body features and the plasma zinc change was found. Length and weight velocities were similar in AGA and SGA infants. These observations indicate that the possibility of increasing plasma zinc level by zinc supplementation depends on gestational age and maturity.(author)