Free triiodothyronine is associated with the occurrence and remission of nonalcoholic fatty liver disease in euthyroid women

Background The association between nonalcoholic fatty liver disease (NAFLD) and free triiodothyronine (FT3) in euthyroid subjects was in dispute. We aimed to investigate this issue in a population-based cohort study. Materials and methods A total of 3144 euthyroid subjects at baseline from the Shanghai Nicheng Atherosclerosis Study were selected for the cross-sectional analysis, and 2089 subjects being followed up after 2.2 years were selected for the longitudinal analysis. NAFLD was diagnosed by ultrasound. The cut-off point of elevated alanine aminotransferase (ALT) level was 40 U/L. The FIB-4 index was used to assess the risk of advanced liver fibrosis. Results Age-adjusted mean levels of FT3 and FT3/free thyroxine (FT4) ratio were higher in subjects with NAFLD than those without NAFLD and linearly increased with a higher risk of NAFLD progression (assessed by levels of ALT and FIB-4 index) in euthyroid women but not in men. After adjustment for confounding variables, FT3 levels significantly increased with the presence of NAFLD (beta = 0.1, P < 0.001) and linearly increased with a higher risk of NAFLD progression in euthyroid women. After a 2.2-year follow-up, FT3 levels increased with the occurrence of NAFLD (mean change percentage: 1.4%) and decreased with the remission of NAFLD (mean change percentage: -2.7%) in euthyroid women. Conclusions There are positive associations of FT3 levels with NAFLD and the risk of NAFLD progression in euthyroid women. The changes in FT3 levels with the alteration of NAFLD status may be an adaptive response to maintain energy and metabolic homeostasis.