Zinc in early life: a key element in the fetus and preterm neonate

Zinc is a key element for growth and development. In this narrative review, we focus on the role of dietary zinc in early life (including embryo, fetus and preterm neonate), analyzing consequences of zinc deficiency and adequacy of current recommendations on dietary zinc. We performed a systematic search of articles on the role of zinc in early life. We selected and analyzed 81 studies. Results of this analysis showed that preservation of zinc balance is of critical importance for the avoidance of possible consequences of low zinc levels on pre- and post-natal life. Insufficient quantities of zinc during embryogenesis may influence the final phenotype of all organs. Maternal zinc restriction during pregnancy influences fetal growth, while adequate zinc supplementation during pregnancy may result in a reduction of the risk of preterm birth. Preterm neonates are at particular risk to develop zinc deficiency due to a combination of different factors: (i) low body stores due to reduced time for placental transfer of zinc; (ii) increased endogenous losses; and (iii) marginal intake. Early diagnosis of zinc deficiency, through the measurement of serum zinc concentrations, may be essential to avoid severe prenatal and postnatal consequences in these patients. Typical clinical manifestations of zinc deficiency are growth impairment and dermatitis. Increasing data suggest that moderate zinc deficiency may have significant subclinical effects, increasing the risk of several complications typical of preterm neonates (i.e., necrotizing enterocolitis, chronic lung disease, and retinopathy), and that current recommended intakes should be revised to meet zinc requirements of extremely preterm neonates. Future studies evaluating the adequacy of current recommendations are advocated.