Human milk microbial species are associated with infant head-circumference during early and late lactation in Guatemalan mother-infant dyadsOriginal paper
Karen Pendergrass is a microbiome researcher specializing in microbiome-targeted interventions (MBTIs). She systematically analyzes scientific literature to identify microbial patterns, develop hypotheses, and validate interventions. As the founder of the Microbiome Signatures Database, she bridges microbiome research with clinical practice. In 2012, based on her own investigative research, she became the first documented case of FMT for Celiac Disease, four years before the first published case study.
Read MoreWhat was studied?
This study asked whether the human milk microbiome is associated with infant head circumference, used as a proxy for brain growth. The milk microbiome had not previously been linked to head circumference. The design was cross-sectional, sampling milk at two lactation stages. Milk bacteria were profiled by 16S ribosomal RNA gene sequencing using the ANCHOR species-level pipeline. Infants were grouped by head-circumference-for-age z-score (HCAZ), split at a cutoff of minus 1 standard deviation. Alpha diversity, constrained ordination, and DESeq2 differential abundance were compared.
Who was studied?
The cohort was 62 unrelated Mayan mothers and their vaginally delivered, breastfed infants in eight rural communities in the Western Highlands of Guatemala. Sampling occurred between June 2012 and January 2013. Milk was sampled at early lactation (6 to 46 days postpartum, 29 dyads) or late lactation (109 to 184 days, 33 dyads). At early lactation, 18 infants had adequate head circumference and 11 were below the cutoff; at late lactation, 14 versus 19. Mothers were healthy, without sub-clinical mastitis or antibiotics.
What were the most important findings?
Across 64 milk samples, 503 sequence variants annotated 256 putative species. Chao1 richness differed between head-circumference groups only at late lactation (p = 0.045), not early lactation. Constrained ordination showed significant community differences between groups at both stages (p = 0.003). DESeq2 identified 26 differentially abundant species overall, 13 at each stage. In early lactation, 12 species were enriched in the adequate-head-circumference group and only 1 in the low group, mostly Firmicutes human colonizers. In late lactation the pattern shifted, with 10 species enriched in the low group, several of environmental or potentially opportunistic origin.
What are the greatest implications of this study?
The findings offer the first evidence that the human milk microbiome is associated with infant head growth, hinting at possible milk-to-brain crosstalk during lactation. Adequate head growth aligned with human-adapted Firmicutes colonizers, whereas smaller heads aligned with more environmental and potentially opportunistic bacteria in late lactation. Because the study was cross-sectional and observational, it cannot show that milk bacteria cause differences in head growth. Species remain putative, the cohort was small and specific, and further investigation is needed.