Objective  To investigate the relationship between the composition of salivary microecology and thyroid-stimulating hormone (TSH) levels in healthy adults.

  Methods  Healthy subjects were included in the high-TSH group (n=22, 3.00-4.20 mIU/L) and the low-TSH group (n=24, 0.60-1.80 mIU/L) according to their TSH level. Clinical and laboratory examinations were conducted to measure and analyze the relevant clinical and biochemical indicators. Saliva samples were collected in the two groups and microbial genetic profiles were acquired by 16S rDNA sequencing and bioinformatics analysis.

  Results  There was no significant difference in the relevant clinical and biochemical indicators between the high-TSH group and the low-TSH group (P>0.05). Individuals with higher TSH levels had higher abundance and species diversity of salivary microbiome. Partial least squares discriminant analysis (PLS-DA) found that the microecology of the the high-TSH group and the low-TSH group (Adonis, P=0.0460) showed obvious differences in β diversity. Wilcoxon rank-sum test and LEFSe analysis showed significant difference in the abundance of Fusobacteriumbetween the high-TSH group and the low-TSH group.

  Conclusion  Differences in the composition of microecology were observed in the saliva of healthy subjects with high TSH levels and those with low TSH levels, and the abundance of Fusobacterium showed the most significant difference between the high and low TSH groups.