Zinc Concentration in Breast Milk Is Inversely Correlated with the Zinc Supplementation Requirements of Preterm Infants

Zinc is an essential trace element that is crucial for numerous biological processes, including protein synthesis, antioxidant activity, and bone calcification. Preterm infants are at high risk of zinc deficiency owing to inadequate zinc stores at birth and the rapid decline in zinc concentration in breast milk. This study aimed to evaluate the relationship between zinc concentrations in breast milk and zinc supplementation in preterm infants. A prospective observational study was conducted at Showa University Hospital, enrolling preterm infants born at less than 32 weeks of gestation or with a birth weight of less than 1800 g. Serum zinc levels, breast milk zinc concentrations, and zinc acetate supplementation were analyzed. The results indicated an inverse correlation between breast milk zinc concentration and the required zinc supplementation dose. Infants receiving high-dose zinc supplementation (≥3 mg/kg/day) had significantly lower breast milk zinc concentrations at 2, 4, and 5 weeks postpartum. These findings highlight the need for individualized zinc monitoring and supplementation strategies to prevent zinc deficiency in preterm infants. Considering the absence of zinc in human milk fortifiers in Japan, aggressive zinc supplementation may be necessary to ensure optimal growth and development.