Metagenomic Analysis of Gut Microbiota Structure and Function in Adults with Subclinical Hypothyroidism: A Cross-Sectional Study in China.

Subclinical hypothyroidism (SCH) is a condition characterized by thyroid hormone dysregulation, often associated with subtle clinical symptoms and metabolic disturbances. Emerging evidence suggests that the gut microbiota plays a crucial role in modulating thyroid function, but the microbiota-thyroid axis in SCH remains poorly understood. This study systematically investigates the gut microbiota composition, functional characteristics, and their correlation with thyroid hormone profiles in SCH patients. Using metagenomic sequencing and thyroid function assessments, we identified significant alterations in the gut microbiota of SCH patients, including a depletion of beneficial microbes such as Blautia and Bifidobacterium, and an enrichment of opportunistic pathogens like Bacteroides and Escherichia. Notably, Blautia depletion was negatively correlated with TSH levels, while Bacteroides abundance positively correlated with TSH levels, further highlighting the role of gut microbiota in thyroid dysfunction. Moreover, functional gene analysis revealed significant alterations in microbial metabolic pathways, with key pathways demonstrating correlations with thyroid hormone levels (free triiodothyronine (FT3) and triiodothyronine (T3)). Our findings suggest that gut microbial dysbiosis is closely associated with SCH. The study provides novel insights into the gut-thyroid axis and its role in SCH, offering new targets for early diagnosis, risk stratification, and intervention strategies in thyroid diseases.