Background Impaired sensitivity to thyroid hormones has been demonstrated to be positively associated with the prevalence of metabolic disorders. However, the relationship between sensitivity to thyroid hormones and metabolic dysfunction-associated fatty liver disease (MAFLD) and liver fibrosis remained unclear. We aimed to determine the associations of thyroid hormone sensitivity indices with MAFLD and its progression to liver fibrosis in Chinese euthyroid adults. Methods 7906 euthyroid adults were included in this community-based study. We calculated the thyroid sensitivity indices, including free triiodothyronine to free thyroxine (FT3/FT4) ratio, thyroid feedback quantile-based index by FT4 (TFQIFT4), and thyroid feedback quantile-based index by FT3 (TFQIFT3), indicate peripheral and central thyroid hormone sensitivity respectively. Liver steatosis and fibrosis were diagnosed by vibration-controlled transient elastography (VCTE). The multivariable logistic/linear regression and restricted cubic spline (RCS) analysis were conducted. Results Compared with participants in quartile 1st (Q1), the prevalence of MAFLD increased by 62% in quartile 4th (Q4) of FT3/FT4 ratio (OR 1.62, 95% CI (1.38, 1.91)) and by 40% in Q4 of TFQIFT3 (OR 1.40, 95% CI (1.18, 1.65)) (both P < 0.05). No associations between TFQIFT4 and the prevalence of MAFLD were found. In addition, compared with participants in Q1, the prevalence of liver fibrosis increased by 45% in Q4 of TFQIFT3 (OR 1.45, 95% CI (1.03, 2.06)) (P < 0.05) in participants with MAFLD. Conclusions Impaired central sensitivity to FT3 was associated with MAFLD and its progression to liver fibrosis. More prospective and mechanism studies were warranted to confirm the conclusions.

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