Serum level of free thyroxine is an independent risk factor for non-alcoholic fatty liver disease in euthyroid people.

BACKGROUND

Non-alcoholic fatty liver disease (NAFLD) has become a major public health problem concern in recent decades. The specific mechanism of NAFLD is still not clear. Previous studies had shown the correlation between NAFLD and thyroid dysfunction. The correlation between thyroid hormones within the euthyroid range and NAFLD has not yet been clarified. This study sought to investigate the association between NAFLD and thyroid hormones in euthyroid patients.

METHODS

A retrospective cross-sectional study was conducted at Beijing Tiantan Hospital from January 1, 2019, to October 1, 2021. Eighty-one NAFLD patients with normal thyroid function and 34 healthy individuals were enrolled. Participants' demographic information, biochemical parameters, and thyroid hormone levels were collected. The severity of NAFLD was assessed by abdominal computed tomography (CT). The association between NAFLD and thyroid hormones was analyzed.

RESULTS

Patients in the NAFLD group were older and more likely to be female than those in the healthy control group (P<0.05). Compared to the healthy control group, the serum levels of fasting plasma glucose (FPG), alanine transaminase (ALT), plasma aspartate transaminase (AST), triglyceride, gamma-glutamyl transferase (γ-GT), and uric acid (UA) were higher, but the levels of high-density lipoprotein cholesterol (HDL-C), and free thyroxine (FT4) were lower in the NAFLD group (P<0.05). NAFLD is more severe in females than males (P<0.05). ALT, AST, low-density lipoprotein cholesterol (LDL-C), γ-GT, tetraiodothyronine, and free triiodothyronine (FT3) levels increased significantly as the severity of NAFLD increased (P<0.05). The results of the Spearman correlation analysis indicated that the severity of NAFLD was positively correlated with ALT (r=0.376, P=0.001), AST (r=0.275, P=0.015), and LDL (r=0.313, P=0.007). The multiple logistic regression analysis showed that age [odds ratio (OR) =1.071; 95% confidence interval (CI): 1.010-1.136, P=0.021], ALT (OR =1.091; 95% CI: 1.034-1.150, P=0.001), HDL-C (OR =0.085; 95% CI: 0.010-0.690, P=0.021), and FT4 (OR =0.738; 95% CI: 0.545-1.001, P=0.046) were independently related to the risk of NAFLD in patients with normal thyroid function.

CONCLUSIONS

FT4 within the normal range was lower in the NAFLD group compared to the healthy control group. The serum level of FT4 is an independent risk factor of NAFLD in euthyroid people.