Thyroid Function and Risk of Non-Alcoholic Fatty Liver Disease in Euthyroid Subjects

Introduction and aims. The association between thyroid function and non-alcoholic fatty liver disease (NAFLD) remained controversial. A large cross-sectional study aimed to explore the relationship in euthyroid population. Material and methods. A total of 1773 euthyroid subjects who underwent health check-up during one-year period were enrolled. NAFLD was diagnosed by ultrasound and fatty liver index (FLI). Fibrosis was estimated by BARD score. Thyroid function parameters, including thyroid-stimulating hormone (TSH), free triiodothyronine (FT3), and free thyroxine (FT4), were recorded. Multivariate logistic regression analyses were performed to identify the independent risk factors. Odds ratios (ORs) with 95% confidence intervals (CIs) were calculated. Results. NAFLD was diagnosed by ultrasound in 638 (35.98%) subjects and by FLI >= 60 in 694 (39.14%) subjects. Regardless of ultrasound or FLI, the overall analysis demonstrated that TSH and FT3 levels were significantly higher in subjects with NAFLD than subjects without NAFLD, but FT4 level was not significantly different between them. This association remained in middle-age subjects, but not elderly subjects. In the multivariate logistic regression analysis, TSH (OR = 1.108, 95% CI = 1.056-1.398, P = 0.024) and FT3 (OR = 1.258, 95% CI = 1.123-1.409, P = 0.000) levels were independently associated with the risk of NAFLD diagnosed by ultrasound; and only FT3 level (OR = 1.252, 95% CI = 1.074 - 1.460, P = 0.004) was independently associated with the risk of NAFLD estimated by FLI >= 60. Additionally, FT3 level (OR = 1.178, 95% CI = 1.025 - 1.354, P = 0.021) was independently associated with the risk of fibrosis estimated by BARD score >= 2 in NAFLD subjects. Conclusion. Among the euthyroid population, FT3 and TSH levels were positively associated with the risk of NAFLD.