Association between Abdominal Fat Distribution and Free Triiodothyronine in a Euthyroid Population

Background: Obesity is closely related to thyroid hormones; however, the relationship between abdominal fat distribution and thyroid hormones has rarely been explored. Objectives: This study aimed to explore the relationship between abdominal fat distribution and free triiodothyronine (FT3) and FT3 to free thyroxine (FT4) ratio (FT3/FT4) in a euthyroid population. Methods: The present study enrolled 1,036 participants (age range 27–81 years; 445 men and 591 women). The visceral fat area (VFA) and the subcutaneous fat area (SFA) were determined by magnetic resonance imaging. FT3, FT4, and thyroid-stimulating hormone were measured by an electrochemical luminescence immunoassay. Results: In both men and women, SFA increased according to the increase of FT3 and FT3/FT4 tertiles ( p for trend <0.05), while VFA did not significantly change. In the multivariate stepwise regression analysis, SFA was independently and positively related to FT3 in both men and women, the standardized β (95% CI) were 0.183 (0.094, 0.272) ( p < 0.001) and 0.089 (0.007, 0.171) ( p = 0.033), respectively. Moreover, SFA was independently and positively related to FT3/FT4 in men, the standardized β (95% CI) was 0.196 (0.101, 0.290) ( p < 0.001). However, VFA was not related to either FT3 or FT3/FT4 in both genders. Conclusions: Abdominal subcutaneous fat was independently related to increased FT3 in a euthyroid population.