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 1 H-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 (ß = -.110, p < .01; ß = .126, p < .05), specifically in males (ß = -.117, p < .05; ß = .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: ß = -.021, p = 0.67; males with T2D: ß = -.033; p = .56). TSH was associated positively with FLI only in male T2D before (ß = .116, p < .05), but not after adjustments for age and BMI (ß = .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.

Intramyocellular Triglyceride Content During the Early Course of Type 1 and Type 2 Diabetes

Intramyocellular lipid content (IMCL) is elevated in insulin-resistant humans, but it changes over time, and relationships with comorbidities remain unclear. We examined IMCL during the initial course of diabetes and its associations with complications. Participants of the German Diabetes Study (GDS) with recent-onset type 1 (n = 132) or type 2 diabetes (n = 139) and glucose-tolerant control subjects (n = 128) underwent 1H-MRS to measure IMCL and muscle volume, whole-body insulin sensitivity (hyperinsulinemic-euglycemic clamps; M-value), and cycling spiroergometry (VO2max). Subgroups underwent the same measurements after 5 years. At baseline, IMCL was ∼30% higher in type 2 diabetes than in other groups independently of age, sex, BMI, and muscle volume. In type 2 diabetes, the M-value was ∼36% and ∼62% lower compared with type 1 diabetes and control subjects, respectively. After 5 years, the M-value decreased by ∼29% in type 1 and ∼13% in type 2 diabetes, whereas IMCL remained unchanged. The correlation between IMCL and M-value in type 2 diabetes at baseline was modulated by VO2max. IMCL also associated with microalbuminuria, the Framingham risk score for cardiovascular disease, and cardiac autonomic neuropathy. Changes in IMCL within 5 years after diagnosis do not mirror the progression of insulin resistance in type 2 diabetes but associate with early diabetes-related complications.

ARTICLE HIGHLIGHTS

Intramyocellular lipid content (IMCL) can be elevated in insulin-resistant humans, but its dynamics and association with comorbidities remain unclear. Independently of age, sex, body mass, and skeletal muscle volume, IMCL is higher in recent-onset type 2, but not type 1 diabetes, and remains unchanged within 5 years, despite worsening insulin resistance. A degree of physical fitness modulates the association between IMCL and insulin sensitivity in type 2 diabetes. Whereas higher IMCL associates with lower insulin sensitivity in people with lower physical fitness, there is no association between IMCL and insulin sensitivity in those with higher degree of physical fitness. IMCL associates with progression of microalbuminuria, cardiovascular disease risk, and cardiac autonomic neuropathy.