Association Between Thyroid Function Parameters and Plasma Branched-Chain Amino and Keto Acids in Patients With Euthyroid Type 2 Diabetes Mellitus.

Objectives: The objective of the study is to determine the association between thyroid function parameters and plasma levels of branched-chain amino acids (BCAAs) and their metabolites, branched-chain keto acids (BCKAs), in patients with euthyroid Type 2 diabetes mellitus (T2DM). Methods: We conducted a cross-sectional study among 357 participants with euthyroid T2DM. Plasma BCAAs and BCKAs were measured using enzyme-linked immunosorbent assay (ELISA), while four thyroid function parameters, including triiodothyronine (T3), thyroxine (T4), free triiodothyronine (FT3), and free thyroxine (FT4), were determined by an automatic biochemical analyzer. The variance inflation factor (VIF) was used to investigate variable collinearity. Pearson correlation and multivariate linear regression analysis were used to establish the relationship between BCAAs or BCKAs and thyroid function parameters. Results: The means of T3, T4, FT3, and FT4 were different among the three groups divided by BCAA tertiles (all p < 0.05), and the means of T3 and FT3 were different among the three groups divided by BCKA tertiles (all p < 0.01). Pearson correlation analysis indicated a positive relationship between all the thyroid function parameters and BCAA levels (p < 0.05), while a statistically significant inverse relationship was established between T3 and FT3 levels and BCKA levels (p < 0.01). Collinearity analysis demonstrated no collinearity among the variables (tolerance: 0.501~0.922; VIF: 1.084~1.995). Multivariate linear regression analysis showed that thyroid function parameters were significantly associated with BCAAs (coefficients: 0.042 to 4.614, p < 0.05) and BCKAs (coefficients: -0.200 to -0.156, p < 0.01) after adjusting for other potential confounding factors. Conclusions: Thyroid function parameters positively correlated with plasma BCAAs but negatively correlated with plasma BCKAs in patients with euthyroid T2DM. However, further prospective studies are needed to explore potential causal relationships and verify these findings.