Low normal thyroid function attenuates serum alanine aminotransferase elevations in the context of metabolic syndrome and insulin resistance in white people.
OBJECTIVE
Thyroid hormones play a key role in hepatic lipid metabolism. Although hypothyroidism is associated with increased prevalence of non-alcoholic fatty liver disease (NAFLD), the relationship of NAFLD with low normal thyroid function is unclear. We tested the association of serum alanine transferase (ALT), as a surrogate of NAFLD, with variations in thyroid function within the normal range.


METHODS
Thyroid stimulating hormone (TSH), free T4, ALT, insulin resistance (homeostasis model assessment (HOMA-IR)) and adiponectin were measured in 82 non-diabetic white subjects with TSH and free thyroxine (free T4) levels within the reference range. Nineteen participants were classified with metabolic syndrome (MetS).


RESULTS
ALT was higher in MetS subjects (p<0.05), coinciding increased HOMA-IR (p<0.001). TSH and free T4 levels were not different in subjects with and without MetS. In all subjects combined, ALT was correlated positively with HOMA-IR and inversely with adiponectin (both p<0.001). Remarkably, ALT was correlated inversely with TSH in subjects with MetS (r=-0.642, p=0.003), but not in subjects without MetS (r=-0.132, p=0.30). Accordingly, in age- and sex-adjusted multivariable linear regression analysis the relationship of ALT with TSH was modified by the presence of MetS (interaction: β=-0.244, p=0.026), and likewise by HOMA-IR (interaction: β=-0.203, p=0.037). TSH also interacted with adiponectin on ALT (interaction: β=0.204, p=0.037).


CONCLUSIONS
Low normal thyroid function may attenuate ALT elevations in the context of MetS and insulin resistance. It is conceivable that effect modification of low normal thyroid function on adiponectin-mediated pathways may be involved.
Department of Endocrinology, The Netherlands; Department of Endocrinology, University of Groningen, The Netherlands. Electronic address: r.p.f.dullaart@umcg.nl.
Robin P F
RP
Dullaart
Department of Gastroenterology and Hepatology, University of Groningen and University Medical Center Groningen, The Netherlands.
Eline H
EH
van den Berg
Department of Endocrinology, The Netherlands; Department of Endocrinology, University of Groningen, The Netherlands.
Melanie M
MM
van der Klauw
Department of Gastroenterology and Hepatology, University of Groningen and University Medical Center Groningen, The Netherlands.
Hans
H
Blokzijl
D000410:Alanine Transaminase / Q000097:blood*; D006706:Homeostasis; D006801:Humans; D007333:Insulin Resistance; D024821:Metabolic Syndrome / Q000097:blood*; D013960:Thyroid Function Tests; D044465:White People
D000410:Alanine Transaminase
Adiponectin; Alanine aminotransferase; Insulin resistance; Metabolic syndrome; Thyroid stimulating hormone