Free triiodothyronine levels are positively associated with non-alcoholic fatty liver disease in euthyroid middle-aged subjects

Background: Studies on the relationship between thyroid function and non-alcoholic fatty liver disease (NAFLD) among euthyroid subjects have produced conflicting results. Objectives: The aim of this study was to investigate the association between thyroid function and the presence of NAFLD in a large-sample middle-aged euthyroid subjects. Methods: A total of 2576 euthyroid subjects who underwent health check-up were included. NAFLD was diagnosed by hepatic ultrasonography. Conventional risk factors for NAFLD were assessed as well as serum levels of TSH, FT3 and FT4. Results: Levels of FT3 were significantly higher in NAFLD group (5.12 +/- 0.58 versus 4.84 +/- 0.58 pmol/L, adjusted p = 0.000) than non-NAFLD group, while levels of TSH and FT4 were comparable between NAFLD and non-NAFLD groups (TSH: 2.13 +/- 0.90 versus 2.20 +/- 0.93 mIU/L, adjusted p = 0.190; FT4: 16.41 +/- 2.04 versus 16.18 +/- 2.06 pmol/L, adjusted p = 0.146, respectively). Levels of FT3 were positively correlated with components of metabolic syndrome. Multivariate logistic regression analysis revealed that high level of FT3 was an independent predictor for NAFLD (odds ratio: 1.253, p = 0.040). The relationship between FT4 and NAFLD in women was different according to menopausal status, with negative association in pre-menopausal women (OR: 0.777, 95% CI: 0.617-0.979, p = 0.032) and null association in post-menopausal women (OR: 1.037, 95% CI: 0.841-1.277, p = 0.736). Conclusions: Our findings suggested that high levels of FT3 were significantly associated with NAFLD among middle-aged euthyroid subjects independently of known metabolic risk factors. A negative correlation of serum FT4 level with NAFLD was only observed in pre-menopausal women.