Association Between Thyroid Function and Body Composition in Type 2 Diabetes Mellitus (T2DM) Patients: Does Sex Have a Role?

BACKGROUND The relationship between thyroid hormones and body anthropometric measures in type 2 diabetes mellitus (T2DM) patients with normal thyroid function is unclear. The purpose of this study was to evaluate the association between thyroid hormones and body composition in euthyroid T2DM patients in men and women. MATERIAL AND METHODS This was a cross-sectional study that included 561 euthyroid T2DM patients. Fasting venous blood was collected to test laboratory indexes. Bioelectric impedance analysis (BIA) was used to measure body composition. Propensity score matching (PSM) was used to enroll patients with similar baseline characteristics. The least absolute shrinkage and selection operator (LASSO) algorithm was used to establish a linear regression model of thyroid hormone and body composition. PSM was performed to match 159 men and 159 women. RESULTS The LASSO regression analysis suggested that thyroid-stimulating hormone (TSH) level was not correlated with body composition parameters in females. In females, free triiodothyronine (FT3) level was positively correlated with body mass index (BMI), fat-free mass index (FFMI), and skeletal muscle index (SMI), and was negatively correlated with extracellular water fraction (EWF). In males, FT3 level was positively correlated with waist circumference (WC) and SMI and negatively correlated with EWF. Free thyroxine (FT4) level in both women and men was positively correlated with body fat mass (BFM) and left lower-limb muscle mass (LLLMM). Moreover, in males, FT4 level was correlated with more body composition parameters. In euthyroid T2DM patients, FT3 level was positively correlated with SMI and negatively correlated with EWF, while FT4 level was positively correlated with BFM and LLLMM. CONCLUSIONS Thyroid function can affect body composition in euthyroid T2DM patients. Thyroid function is more likely to affect the fat and muscle distribution of males than females.