Serotonin and the gut microbiome: Pathways, functions, and health implications

Serotonin, an evolutionarily conserved molecule produced in the gut, plays a multifaceted role in host physiology. Several organs within the host can directly synthesize serotonin, yet its activity and secretion are intricately linked to the gut microbiome through both direct and indirect pathways. The gut microbiome significantly influences serotonin biosynthesis across the lifespan, with fluctuations reflecting parallel changes in serotonin levels. Dysbiosis of gut microbiota is associated with serotonergic dysfunction, contributing to various health disorders. Prebiotics and probiotics have shown the potential to modulate these effects and ameliorate related health issues. The interactions between the gut microbiome and serotonin metabolism underscore the importance of maintaining healthy microbiota for optimal serotonin function and overall health. This review explores the pathways through which the gut microbiome influences serotonin, its functions, and its implications for health, highlighting the therapeutic potential of targeting the gut microbiota to regulate serotonin levels. • Gut microbes directly synthesize serotonin via specific microbial enzymes • Microbial metabolites like SCFAs indirectly enhance gut serotonin synthesis • Dysbiosis alters serotonin levels, affecting neurological and immune health • Probiotics modulate serotonin pathways, offering therapeutic potential • Microbiome-serotonin interactions change dynamically across the lifespan