The Gut Microbiome in Early Ontogeny: Implications for Brain and Immune System Development

The gut microbiome plays a pivotal role in modulating multiple physiological processes from the earliest stages of life. However, the complete scope of its effects during childhood is yet to be fully elucidated, which underscores the importance of enhancing the understanding of this emerging area of research. This narrative review provides an overview of the influence of the gut microbiome in early human ontogeny by examining its role in brain and immune development, as well as its involvement in neurodevelopmental disorders and early-life mental health. The gut microbiome contributes to shaping the development and function of both the brain and the immune system. Its influence appears to be primarily mediated through the synthesis of neurotransmitters and microbial metabolites, as well as through the activation of specific pathways within the hypothalamic–pituitary–adrenal axis. Nevertheless, the exact mechanisms through which the gut microbiome exerts these effects, and the full extent of its impact on neurodevelopmental and immune health, remain incompletely understood and continue to be active areas of research and scientific debate. Ultimately, advances revealing how the gut microbiome shapes early brain and immune system development will create new opportunities for innovative interventions and predictive strategies aimed at transforming pediatric health outcomes.