Zinc Content in Breast Milk and Its Association with Maternal Diet

Background: Zinc is an indispensable element, being involved in many biological processes. Correspondingly, insufficient zinc intake in early youth can detrimentally affect the function of a growing body. The aim of this study was to determine zinc content in breast milk among lactating women in Latvia and factors (maternal diet; mother's and baby's characteristics; breastfeeding pattern) affecting it. Methods: In total, 62 mature milk (at least one month postpartum) samples were collected and pooled within 24 h. Zinc content (mg 100 mL(-1)) was determined using inductively coupled plasma mass spectrometry (ICP-MS; Agilent 7700x, Agilent Technologies, Tokyo, Japan). Results: Zinc content in mature breast milk ranged from 0.01 to 0.34 mg 100 mL(-1) with a median (interquartile range) content of 0.10 (0.05-0.15) mg 100 mL(-1). Time postpartum was a significant negative predictor for zinc content in breast milk (r = -0.500; p = 0.000). Median maternal zinc intake was 10.70 (7.24-15.27) mg. Yet, zinc content in breast milk was unaffected by maternal dietary zinc intake (r = 0.155; p = 0.221). Conclusions: Maternal dietary zinc intake was nearly the recommended intake for lactating women (11 mg), but due to low zinc content in breast milk, babies in Latvia might not receive sufficient zinc intake. Future research should aim for the assessment of zinc status by evaluating plasma or serum levels of both mothers and babies.