Influence of Newborns' Sex on Minor and Trace Element Concentrations in Human Milk During Early Lactation.

Objectives: This study aimed to investigate the influence of newborns' sex on the concentrations of minor and trace elements in the human milk of lactating mothers during early lactation. The elemental analysis focused on calcium (Ca), potassium (K), sodium (Na), and chlorine (Cl) as minor elements and iodine (I), aluminum (Al), bromine (Br), and rubidium (Rb) as trace elements. Methods: Breast milk samples were collected from 75 lactating mothers in Tehran, Iran, during the early feeding stage. Neutron activation analysis was used to quantify elemental amounts in milk samples, and t tests were conducted to identify statistical differences in element levels between mothers of male and female newborns. Results: Statistically significant differences in the elemental composition of milk samples were found based on newborn infants' sex. Mothers of female newborns had notably higher mean levels of Br (14.8 mg/kg versus 11.3 mg/kg, p = 0.011), Cl (10.16 mg/g versus 7.10 mg/g, p = 0.009), and Na (6.18 mg/g versus 4.45 mg/g, p = 0.017) compared with mothers with male newborns. Although Ca, K, I, Al, and Rb did not show statistically substantial differences, there was a trend toward elevated levels of Al, I, and Ca in the milk of mothers with the females. Conclusion: The analysis reveals sex-based variations in human milk composition, with elevated levels of Br, Cl, and Na observed in mothers of female newborns. These findings suggest that infant sex may influence the elemental profile of maternal milk, highlighting the need for further research to uncover the mechanisms behind these differences and their potential implications for improving infant nutrition and health.