Background Human milk is characterised by its complex composition, consisting of nutrient and bioactive components that play a crucial role in infant health. Although the infant oral cavity is directly exposed to these components during breastfeeding, their effects on the developing oral microbiome remains underexplored. This study aimed to assess associations between the concentrations and daily estimated intakes of human milk components (including minerals, lactose, and antimicrobial proteins) and the oral microbiome of exclusively breastfed infants. Methods We profiled infant oral samples collected at 3 months of age using full-length 16S rRNA gene sequencing, alongside paired analyses of human milk components from 45 mother-infant dyads in the Western Australian BLOSOM cohort. Concentrations of milk lactose, antimicrobial proteins (AMPs), and micronutrients (16 components in total) were measured, and their daily estimated intakes were calculated based on 24-hour milk intake. Results The composition of the infant oral microbiome was significantly associated with a number of AMPs and micronutrients, with concentration exerting a far stronger effect than estimated intakes. Lactose, the major sugar in human milk, was not associated with any feature of the infant oral microbiome. Both concentrations and estimated intakes of lactoferrin (P = 0.032 and P = 0.005, respectively), as well as estimated intakes of sodium and iodine (P = 0.041 and 0.022, respectively) were negatively associated with infant oral Shannon diversity. While some associations were consistent when both estimated intakes and concentrations were analysed, some appeared only in one analysis, suggesting differing mechanisms of action. Conclusion These findings underscore the influence of human milk composition on the developing oral microbiome during early life, highlighting that local, concentration-driven mechanisms are the primary drivers of these effects.
Arishi et al. (Thu,) studied this question.