Gut microbiota and its metabolites with thyroid diseases: functions and mechanisms

The gut microbiota, a complex and dynamic ecosystem of microorganisms residing in the gastrointestinal tract, has emerged as a critical regulator of human physiology, extending its influence far beyond digestion. Recent advances have illuminated the existence of a bidirectional communication network known as the "gut-thyroid axis" which posits that the intestinal microbial community and its vast repertoire of bioactive metabolites are fundamental modulators of thyroid health and disease pathogenesis. This comprehensive academic review synthesizes current evidence to elucidate the multifaceted functions and mechanisms through which gut microbiota and its metabolites, such as short-chain fatty acids, secondary bile acids, and lipopolysaccharides, impact thyroid disorders. We detail how these microbial components regulate systemic immunity, influence thyroid hormone metabolism, maintain intestinal barrier integrity, and modulate nutrient absorption, thereby contributing to the development and progression of autoimmune thyroid diseases, thyroid dysfunction, and potentially thyroid cancer. Furthermore, the review discusses the translational implications of this knowledge, including the potential for microbiota-targeted interventions like probiotics, prebiotics, and dietary modifications as adjunctive strategies in thyroid disease management. By integrating findings from human studies and animal models, this review aims to provide a mechanistic framework for understanding the gut-thyroid connection and to highlight promising avenues for future research and precision medicine approaches in endocrinology.