Association of thyroid function with non-alcoholic fatty liver disease in recent-onset diabetes

Background and Aims: Non-alcoholic fatty liver disease (NAFLD) has been linked to type 2 diabetes (T2D), but also to hypothyroidism. Nevertheless, the relationship between thyroid function and NAFLD in diabetes is less clear. This study investigated associations between free thyroxine (fT4) or thyroid-stimulating hormone (TSH) and NAFLD in recent-onset diabetes. Methods: Participants with recent-onset type 1 diabetes ( T1D, n = 358), T2D (n = 596) or without diabetes (CON, n = 175) of the German Diabetes Study (GDS), a prospective longitudinal cohort study, underwent Botnia clamp tests and assessment of fT4, TSH, fatty liver index (FLI) and in a representative subcohort 1H-magnetic resonance spectroscopy. Results: First, fT4 levels were similar between T1D and T2D ( p =.55), but higher than in CON (T1D: p <.01; T2D: p <.001), while TSH concentrations were not different between all groups. Next, fT4 correlated negatively with FLI and positively with insulin sensitivity only in T2D (beta = -.110, p <.01;beta =.126, p <.05), specifically in males (beta = -.117, p <.05; beta =.162; p <.01) upon adjustments for age, sex and BMI. However, correlations between fT4 and FLI lost statistical significance after adjustment for insulin sensitivity (T2D: beta = -.021, p = 0.67; males with T2D: beta = -.033; p =.56). TSH was associated positively with FLI only in male T2D before (beta =.116, p <.05), but not after adjustments for age and BMI (beta =.052; p =.30). Conclusions: Steatosis risk correlates with lower thyroid function in T2D, which is mediated by insulin resistance and body mass, specifically in men, whereas no such relationship is present in T1D.