Impact of thyroid function on the prevalence and mortality of metabolic dysfunction-associated fatty liver disease

Abstract Purpose Thyroid function variation within thyroxine reference range has negative metabolic effects. Metabolic dysfunction-associated fatty liver disease (MAFLD) is a recently proposed definition. We aim to explore the effects of thyroid function status on prevalence and mortality of MAFLD. Methods Data of 10,666 participants from the Third National Health and Nutrition Examination Survey (NHANES III) were used. MAFLD was diagnosed based on the new definition. Thyroid function variation within thyroxine reference range was defined based on thyroid stimulating hormone (TSH) levels as following: subclinical hyperthyroidism, < 0.39 mIU/L; strict-normal thyroid function, 0.39–2.5 mIU/L; and low thyroid function, > 2.5 mIU/L, which was the combination of low-normal thyroid function (2.5–4.5 mIU/L) and subclinical hypothyroidism (> 4.5 mIU/L). Logistic and cox regression were used in multivariate analysis. Results Low thyroid function is independently associated with MAFLD (Odds ratio: 1.27). Compared with strict-normal thyroid function, subclinical hypothyroidism was significantly associated with increased risk for all-cause and cardiovascular mortality in total population (Hazard ratio [HR] for all-cause: 1.23; cardiovascular: 1.65) and MAFLD population (HR for all-cause: 1.32; cardiovascular: 1.99), meanwhile, with low-normal thyroid function group, increasing trend in mortality risk was observed. Furthermore, low thyroid function also showed significant negative impact on mortality in total and MAFLD population. Among thyroid function spectrum, mild subclinical hypothyroidism showed the highest HRs on mortality. Conclusions Low thyroid function is independent risk factor of MAFLD and is associated with increased risk for all-cause and cardiovascular mortality in MAFLD population. Reevaluation of TSH reference range should be considered.