Gut Microbiota-Mediated Modulation of Intestinal Serotonin by Tea Polyphenols: Potential Mechanisms and Implications for Metabolic Health

Tea polyphenols (TPs), the primary bioactive components derived from tea, play an important role in maintaining gut function and metabolic homeostasis. Emerging evidence indicates that the regulatory functions of TP within the intestine are intricately linked to their interactions with the gut microbiota. Serotonin (5-hydroxytryptamine, 5-HT), a key signaling molecule in the gastrointestinal tract, has been implicated in preserving intestinal function and metabolic health. Notably, the modulation of gut microbiota by TPs, the microbial biotransformation of TPs into bioactive metabolites, and the potential regulation on intestinal 5-HT homeostasis may collectively constitute an interconnected axis relevant to gut health and metabolic balance. However, direct experimental evidence linking these components into a unified mechanistic pathway remains limited, and the molecular basis of this putative TP–microbiota–5-HT axis requires further validation. This review systematically summarizes and discusses the regulatory effects of TPs on gut microbiota, and the microbial biotransformation of TPs into metabolites, as well as the microbial modulation of intestinal 5-HT and the roles of 5-HT and its receptors in intestinal function and homeostasis, with a particular focus on critically evaluating the extent to which current data support the proposed interactions among TPs, gut microbiota, and 5-HT in metabolic disorders. A deeper understanding of this tripartite interaction may ultimately inform the development of TP-based dietary approaches targeting gut microbiota–5-HT interactions in gut function and metabolic health, although such translational applications remain speculative in the absence of robust causal evidence.