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Association between thyrotropin levels and insulin sensitivity in euthyroid obese adolescents.

Thyroid : official journal of the American Thyroid Association (2015-03-18)
Asma Javed, P Babu Balagopal, Adrian Vella, Philip R Fischer, Francesca Piccinini, Chiara Dalla Man, Claudio Cobelli, Paula D Giesler, Jeanette M Laugen, Seema Kumar
ABSTRACT

Thyrotropin (TSH) levels display a positive association with body mass index (BMI), and the prevalence of isolated hyperthyrotropinemia is higher in obese adolescents compared to their normal weight controls. However, the metabolic significance of the higher TSH in obese adolescents is less clear. The objective of this study was to determine the relationship between TSH concentrations and insulin sensitivity, lipids, and adipokines in euthyroid, non-diabetic, obese adolescents. Thirty-six euthyroid, non-diabetic, obese adolescents between the ages of 12 and 18 years underwent a 75 g oral glucose tolerance test. Insulin sensitivity (Si) and pancreatic β-cell function as assessed by disposition index (DI) were measured using the oral glucose minimal model approach. Cholesterol (total, low-density lipoprotein [LDL-C], and high-density lipoprotein [HDL-C]), triglycerides (TG), interleukin-6 (IL-6), total and high molecular weight (HMW) adiponectin, and retinol binding protein-4 (RBP4) were also determined. Associations between measures of thyroid function and Si, DI, lipids, and adipokines were computed using Pearson's correlation coefficient and multiple regression analysis. The mean age of the subjects was 14.3±1.88 years, and the mean BMI was 32.5±4.65 kg/m2; 97% were non-Hispanic white and 47% were male. The mean TSH was 2.7±1.2 mIU/L. Increasing serum TSH was correlated with decreasing Si (log Si) in the entire cohort (p=0.03), but this relationship persisted only in males (p=0.02). The correlation between TSH and Si in males remained significant after adjusting for BMI (p=0.02). There was no correlation between TSH and pancreatic β-cell function as assessed by DI (p=0.48). TSH correlated positively with LDL-C (p=0.04) and IL-6 (p=0.03), but these associations vanished or weakened after adjusting for BMI (LDL-C p-value=0.44; IL-6 p-value=0.07). This study suggests a sex-specific association between TSH and insulin sensitivity in euthyroid, non-diabetic, obese adolescent males. Prospective studies are warranted to explore further this sexual dimorphism in the relationship between thyroid function and insulin sensitivity and to determine if obese adolescents with insulin resistance receiving thyroid supplements for hypothyroidism would benefit from targeting TSH levels in the lower half of normal range.

MATERIALS
Product Number
Brand
Product Description

Sigma-Aldrich
Cholesterol, from sheep wool, ≥92.5% (GC), powder
Sigma-Aldrich
Cholesterol, powder, BioReagent, suitable for cell culture, ≥99%
Sigma-Aldrich
Retinol, synthetic, ≥95% (HPLC), crystalline
Sigma-Aldrich
Retinol, ≥95.0% (HPLC), ~2700 U/mg
Sigma-Aldrich
Retinol, BioXtra, ≥97.5% (HPLC), ~3100 U/mg
Sigma-Aldrich
Cholesterol, Sigma Grade, ≥99%
SAFC
Cholesterol, from sheep wool, Controlled origin, meets USP/NF testing specifications
Sigma-Aldrich
Cholesterol, Vetec, reagent grade, ≥92.5%
SAFC
Cholesterol, Plant-Derived, SyntheChol®, NF, Ph. Eur., JP