The human microbiome and its role in health and disease

Abstract

The human microbiome encompasses trillions of microorganisms, including bacteria, archaea, fungi, viruses, and protozoa, colonizing virtually every body surface. These communities contribute to digestion, immune regulation, metabolic homeostasis, and protection against pathogens. Disruption of microbial balance, termed dysbiosis, is associated with conditions spanning gastrointestinal, metabolic, neurological, psychiatric, immune-mediated, cardiovascular, and renal diseases. This narrative review synthesizes current evidence on microbiome composition, function, and clinical significance across health and disease. We address early-life microbiome establishment, site-specific microbial communities, and mechanisms linking microbial imbalance to disease pathogenesis, including the gut-brain, gut-skin, and gut-kidney axes. We distinguish microbial associations from causal relationships, acknowledge research limitations, and outline emerging therapeutic strategies, including probiotics, prebiotics, Fecal Microbiota Transplantation (FMT), and precision microbiome-based medicine. Future research should prioritize longitudinal multi-omics studies, diverse population sampling, and standardized methodologies.