The human gut microbiome across the life course

Across the human lifespan, the gut microbiome exhibits considerable inter-individual variation. However, individuals within the same age group often share characteristic compositional and functional patterns shaped by factors such as early microbial seeding, lifelong environmental exposures, and age-related physiological changes. Birth and early feeding establish the initial gut microbiome, with maternal transmission and milk-derived substrates typically favoring Bifidobacterium. As infants transition to solid foods and experience increasing social and environmental exposures, the microbiome undergoes substantial restructuring throughout childhood and adolescence. In adulthood, functional redundancy underpins stability despite routine perturbations; later life brings greater compositional uniqueness, with some profiles losing core taxa and accommodating opportunistic species, whereas others, particularly healthy older adults and centenarians, retain distinctive metabolic capacities that may buffer inflammaging. Efforts to build microbiome "aging clocks" highlight potential to index biological age, but progress remains constrained by technical and methodological limitations and is still maturing. This review synthesizes current evidence and identifies priorities for developing microbiome-informed, life-stage-tailored interventions.