Human milk is important for infant development, but few large studies have comprehensively investigated milk composition. Here, we characterized human milk oligosaccharides (HMOs) and milk microbiota, their shaping factors, and their links to infant gut microbiota in the longitudinal Dutch Lifelines NEXT cohort. We measured 24 HMOs in 1,542 milk samples from 524 mothers at 0.5-6 months postpartum, profiled microbiota in milk and maternal and infant feces, genotyped mothers, and recorded 174 environmental, maternal, and infant characteristics. HMO concentrations were associated with maternal genetic loci (FUT2, FUT3/FUT6, ABO, and ST3GAL6), lactation stage, and subclinical mastitis. The human milk microbiota varied during lactation and with different feeding practices. Both HMOs and milk microbiota remained stable across multiple pregnancies in the same individual. Some milk bacteria were present in infant feces, but the milk and infant fecal microbiota diverged as the infant aged. Furthermore, individual HMOs were associated with infant fecal microbiota characteristics.
Keywords: CP: Microbiology; bacterial sharing; breastfeeding; early life; genetics; gut microbiota; human milk microbiota; human milk oligosaccharide; infant feeding; infant health; longitudinal.