Iron, zinc, and copper concentrations in breast milk are independent of maternal mineral status

Abstract

Little is known about the regulation of iron, zinc, and copper in breast milk and the transport of these minerals across the mammary gland epithelium. The objective was to study associations between breast-milk concentrations of iron, zinc, and copper and maternal mineral status. Milk samples from 191 Swedish and Honduran mothers were collected at 9 mo postpartum. Iron, zinc, and copper concentrations were measured by atomic absorption spectrometry. Blood samples from mothers were analyzed for plasma zinc and copper and 4 indexes of iron status: hemoglobin, plasma ferritin, soluble transferrin receptors, and zinc protoporphyrin. Complementary food energy (CFE) intake was used as an inverse proxy for breast-milk intake. Mean (+/-SD) breast-milk concentrations of iron were lower in the Honduran than in the Swedish mothers (0.21 +/- 0.25 compared with 0.29 +/- 0.21 mg/L; P < 0.001), and mean breast-milk concentrations of zinc and copper were higher in the Honduran than in the Swedish mothers [0.70 +/- 0.18 compared with 0.46 +/- 0.26 mg/L (P < 0.001) and 0.16 +/- 0.21 compared with 0.12 +/- 0.22 mg/L (P = 0.001), respectively]. Milk iron was positively correlated with CFE intake (r = 0.24, P = 0.001) but was not significantly correlated with any iron-status variable. Milk zinc was negatively correlated with CFE intake (r = -0.24, P = 0.001) but was not significantly correlated with maternal plasma zinc. Milk copper was not significantly correlated with CFE intake or maternal plasma copper. Milk iron, zinc, and copper concentrations at 9 mo postpartum are not associated with maternal mineral status, which suggests active transport mechanisms in the mammary gland for all 3 minerals. Milk iron concentrations increase and milk zinc concentrations decrease during weaning [corrected]