Association of free triiodothyronine and total triiodothyronine with nonalcoholic fatty liver disease: from National Health and Nutrition Examination Survey and Mendelian randomization study.

BACKGROUND

Nonalcoholic fatty liver disease (NAFLD) is associated with multiple factors, yet the relationship between NAFLD and thyroid-related biomarkers remains unclear. This study aims to elucidate this potential linkage.

METHODS

Utilizing data from the US National Health and Nutrition Examination Survey (NHANES), we explored the possible associations between thyroid-related biomarkers and NAFLD through multivariable logistic regression, subgroup analysis, and interaction tests. A bidirectional Mendelian randomization (MR) approach complemented by various sensitivity analyses was then employed to ascertain these relationships' causality.

RESULTS

Our NHANES analysis indicated significant associations between elevated levels of free triiodothyronine (FT3) [odds ratio (OR): 2.59, 95% confidence interval (CI): 1.50-4.49] and total triiodothyronine (TT3) (OR: 2.01, 95% CI: 1.27-3.18) with the prevalence of NAFLD. MR findings reinforced the causal relationship, demonstrating that NAFLD may elevate FT3 ( β : 0.05, 95% CI: 0.01-0.09) and TT3 ( β : 0.08, 95% CI: 0.02-0.14) levels. Additionally, thyroid-stimulating hormone (TSH) was confirmed as an independent risk factor for NAFLD (OR: 1.10, 95% CI: 1.04-1.18), with specific MR sensitivity analyses supporting the robustness of these results.

CONCLUSION

This study indicates potential elevations in FT3, TT3, and thyroglobulin levels associated with NAFLD, while also identifying TSH as a risk factor for NAFLD. These findings underscore the importance of routine thyroid function monitoring both in the general population and particularly in individuals with NAFLD.