DEVELOPMENT, COMPOSITIONAL DYNAMICS AND DETERMINING FACTORS OF THE HUMAN MICROBIOTA: A LIFESPAN PERSPECTIVE

The human microbiota is a dynamic microbial ecosystem that begins to develop at birth and changes throughout the lifespan. The onset of microbial colonization is closely associated with the mode of delivery, with marked early compositional differences observed between vaginally and cesarean-born infants. In the postnatal period, feeding practices-particularly breastfeeding and the presence of human milk oligosaccharides-play a fundamental role in shaping the gut microbiota. Early-life antibiotic exposure, prematurity, and neonatal intensive care unit management may influence microbial diversity and functional maturation. With the introduction of complementary feeding, the gut microbiota undergoes structural and functional reorganization, accompanied by increased production of short-chain fatty acids and a transition toward adult-like microbial characteristics. During early childhood, microbiota development proceeds through successive phases and reaches a more stable configuration by approximately 2-4 years of age. Throughout this period, diet, infections, and antibiotic exposure represent key determining factors. In adulthood, the gut microbiota remains relatively stable but continues to be responsive to diet, lifestyle, medication use, and environmental influences. With advancing age, alterations in microbial diversity, reductions in beneficial taxa, and increases in potential pathobionts have been reported. Physiological states such as pregnancy, menopause, and advanced age represent distinct contexts in which notable shifts in microbiota composition occur. Overall, microbiota composition and functional capacity are dynamically shaped by the combined effects of biological and environmental factors acting across different stages of life.