Objective: To explore the relationship between body fat mass/muscle mass ratio (F/M) and thyroid hormone sensitivity in the euthyroid population.

Methods: Body compositions of 845 check-up individuals were determined using bioelectrical impedance analysis (BIA). Biochemical indexes including blood glucose, blood lipids, liver and kidney functions and thyrotropic hormones (THs) were detected. Free triiodothyronine to free thyroxine ratio (FT3/FT4), Thyroid Feedback Quantile-based Index (TFQI), Thyrotropin Thyroxine Resistance Index (TT4RI) and TSH Index (TSHI) were calculated for analysis.

Results: TT4RI and TSHI showed increased trends with statistical difference, while FT3/FT4 and TFQI showed no difference among F/M quartile groups. After adjusting for confounding factors, F/M exhibited no correlation with FT3/FT4, but positive correlations with TFQI, TT4RI and TSHI. Gender subgroup analysis showed that F/M exhibited positive relationship with TFQI in females; exhibited positive correlations with TFQI, TT4RI and TSHI before the inflection points, but no correlations thereafter in males. Age subgroup analysis showed that F/M exhibited positive correlations with TFQI, TT4RI and TSHI, but no correlation with FT3/FT4 in age < 65 years group; exhibited no relationship with thyroid hormone sensitivity in age ≥ 65 years group. BMI subgroup analysis showed that F/M exhibited no relationship with thyroid hormone sensitivity in BMI < 25 kg/m² group; exhibited positive correlations with TFQI, TT4RI and TSHI before the inflection points, but no correlations thereafter in BMI ≥ 25, < 30 kg/m² group; exhibited positive correlation with TFQI before the inflection point, but no correlation thereafter in BMI ≥ 30 kg/m² group; exhibited no correlations with TT4RI and TSHI before the inflection points, but negative correlations with them thereafter in BMI ≥ 30 kg/m² group.

Conclusion: Impaired central, but not peripheral sensitivity to thyroid hormones was associated with increased body fat mass/muscle mass ratio (F/M), this association was obvious in males, individuals with age < 65 years and BMI ≥ 25 kg/m², with different inflection points. Maybe F/M independently affects thyroid hormone sensitivity, we need more clinical and basic studies in the future.

Keywords: Body fat mass/muscle mass ratio; Free triiodothyronine to free thyroxine; TSH index; Thyroid feedback quantile-based Index; Thyrotropin thyroxine resistance index.

© 2025. The Author(s).

目标： 探索正常甲状腺功能人群中身体脂肪质量/肌肉质量比（F/M）与甲状腺激素敏感性的关系。

方法： 采用生物电阻抗分析法（BIA）测定845名体检个体的身体成分。检测包括血糖、血脂、肝肾功能和促甲状腺激素在内的生化指标。计算游离三碘甲腺原氨酸与游离甲状腺素比值（FT3/FT4）、甲状腺反馈分位数指数（TFQI）、促甲状腺素甲状腺素抵抗指数（TT4RI）和TSH指数（TSHI），进行分析。

结果： TT4RI和TSHI在不同F/M四分位数组间呈增加趋势，且有统计学差异；而FT3/FT4和TFQI则无显著性差异。校正混杂因素后，F/M与FT3/FT4无相关性，但与TFQI、TT4RI和TSHI均呈正相关。性别亚组分析显示，女性的F/M与TFQI呈正相关；男性在拐点前F/M与TFQI、TT4RI和TSHI均有正相关，而在拐点后无显著相关性。年龄亚组分析发现，在

结论： 中心但非外周甲状腺激素敏感性的受损与增加的身体脂肪质量/肌肉质量比（F/M）有关，这种关联在男性、

关键词： 身体脂肪质量/肌肉质量比；游离三碘甲腺原氨酸与游离甲状腺素比例；TSH指数；甲状腺反馈分位数指数；促甲状腺素甲状腺素抵抗指数。