Longitudinal Changes of Bioactive Proteins in Tibetan Human Milk and Their Association with Maternal and Infant Factors

Due to the unique and harsh geographical and climatic conditions at high altitudes, longitudinal studies on the composition of human milk (HM) in Tibet are important but scarce, particularly those investigating the dynamic changes of HM bioactive proteins. This study adopted a longitudinal study design to analyze the concentrations of immunoglobulin A (IgA), IgM, IgG, secretory IgA (SIgA), β-casein, κ-casein, and lactoferrin in HM from 33 Tibetan mothers at 2, 4, and 6 months after delivery using enzyme-linked immunosorbent assay. The influence of related maternal and infant factors on the contents was also analyzed. The results showed that the concentrations of SIgA and IgA were significantly higher at 6 months postpartum than those at 4 months postpartum (56.4 ± 6.3 mg/L vs. 46.4 ± 16.2 mg/L, P = 0.015; and 1769.8 ± 250.1 mg/L vs. 1220.4 ± 365.7 mg/L, P = 0.014, respectively), while other proteins showed no significant differences from 2 to 6 months. The increase of SIgA and IgA may be closely related to maternal immune adaptation and infants' exposure to the environment. The maternal immune system perceives pathogens in the environment and dynamically regulates the content of immunoglobulin in HM. Correlation analysis and generalized estimating equation analyses revealed that maternal occupation, maternal height, gestational weight gain, post-pregnancy body mass index, infant birth weight, and infant birth length influenced the levels of the seven HM bioactive proteins to varying degrees. These findings highlight the dynamic nature of HM bioactive proteins in Tibetan mothers and the impact of maternal and infant factors, offering insights for developing early nutrition strategies and infant formula tailored to the specific needs of Tibetan infants.