Association of thyroid autoimmunity with nonalcoholic fatty liver disease in euthyroid middle-aged subjects: A population-based study

Background and Aim The association between thyroid autoimmunity and nonalcoholic fatty liver disease (NAFLD) remains unclear. In this study, we aimed to investigate the relationship between thyroid autoimmunity and NAFLD in a large cohort of euthyroid subjects. Methods We analyzed clinical and biochemical data from a nationwide, population-based, cross-sectional survey (KNHANES VI). A total of 1589 middle-aged participants aged 45-65 years, with normal thyroid function, were included in this study. NAFLD was defined as a hepatic steatosis index of > 36. We estimated the odds ratios (ORs) for NAFLD according to anti-thyroid peroxidase antibody (TPOAb) positivity by using logistic regression models, and adjusted for potential confounders. Results Overall, 24% (n = 378) of the subjects had NAFLD. Subjects with NAFLD showed a higher positivity for TPOAb (11% vs 7%, P = 0.014) compared with those without NAFLD. TPOAb positivity was a significant risk factor for NAFLD [OR 1.668, 95% confidence interval (CI) 1.019-2.730, P = 0.042] even after adjusting for confounding variables, including age, sex, household income, education, smoking, alcohol consumption, walking activity, abdominal obesity, elevated blood pressure, dyslipidemia and hyperglycemia. In addition, TPOAb positivity predicted the risk of advanced liver fibrosis (OR 3.112, 95% CI 1.256-7.713, P = 0.014) in subjects with NAFLD, independent of the confounding variables. Conclusion In euthyroid subjects, thyroid autoimmunity is associated with NAFLD and advanced liver fibrosis, independent of known metabolic risk factors. Large longitudinal studies in the future will help clarify the causality.