Human milk metals and metalloids shape infant microbiota Original paper

What was studied?

This study investigated the relationship between the metal(loid) content in human milk and its influence on the infant gut microbiota. Specifically, it aimed to explore how variations in metals such as iron (Fe), manganese (Mn), zinc (Zn), copper (Cu), and others affect the microbiota during the early lactation stage (7-15 days postpartum) and the mature lactation stage (30-60 days postpartum). The study analyzed human milk (HM) samples and infant stool samples from 77 mother-infant pairs using metallomic profiling and 16S rRNA sequencing to examine microbial abundances, richness, and diversity. The study used statistical tools like Spearman’s rank correlation to explore metal-microbiota interactions and their potential effects on infant gut development.

Who was studied?

The study focused on 77 healthy mother-infant dyads from the MAMI cohort. The mothers provided human milk samples, while stool samples were collected from their infants at two different time points: the early transitional lactation stage and the mature lactation stage. The infants were not exposed to any antibiotics during the study period, ensuring that the effects observed were due to natural variations in the metal content of human milk and the corresponding gut microbiota development.

What were the most important findings?

The study found significant differences in the concentrations of metals between the early and mature stages of lactation. For instance, cobalt (Co), copper (Cu), zinc (Zn), molybdenum (Mo), and antimony (Sb) were significantly lower in mature human milk compared to early lactation stages. In terms of microbiota, the relative abundance of Bifidobacterium was higher in infant stool samples during the mature lactation stage. Additionally, the study identified various correlations between metal concentrations in human milk and microbial abundances in infant feces. Notably, during early lactation, a positive correlation was found between nickel concentrations in human milk and the abundance of Corynebacterium in the infant gut, while negative correlations were observed between copper and Enterobacter spp., as well as antimony and Veillonella spp. In the mature lactation stage, the Klebsiella genus exhibited multiple negative correlations with metals such as iron, antimony, and vanadium. Additionally, the study noted that higher levels of metal diversity in human milk were associated with increased alpha diversity in the infant gut microbiota, particularly during the mature lactation phase.

What are the greatest implications of this study?

The findings of this study highlight the crucial role of metals in shaping the infant gut microbiota during the first months of life. The metal(loid) content in human milk, which varies over the course of lactation, has the potential to influence microbial growth and metabolism. Understanding these relationships can help inform better breastfeeding practices and maternal health strategies, particularly in regions where environmental exposure to metals could affect both maternal milk and infant gut health. The study also sheds light on the role of specific microbes, such as Bifidobacterium, Klebsiella, and Enterobacter, which appear to be particularly sensitive to metal fluctuations, influencing microbial richness and diversity in the infant gut. The findings suggest that future research should delve deeper into the mechanisms by which metal(loid)s influence gut microbiota at the strain level and explore the long-term implications for infant health, immunity, and metabolic development.