Central sensitivity to thyroid hormones is reduced in youths with overweight or obesity and impaired glucose tolerance

Background: Thyroid hormones (TH) play multiple effects on glucose metabolism. Some recent studies carried out in adult patients suggested an association between altered sensitivity to TH and type 2 diabetes, obesity, and metabolic syndrome. No studies are currently available on the presence of altered sensitivity to the action of TH in youths with prediabetes.

Objective: To evaluate the relationship between sensitivity to TH and impaired glucose tolerance (IGT), impaired fasting glucose (IFG), or glycosylated hemoglobin (HbA1c) ≥ 5.7% in youths with overweight/obesity (OW/OB).

Materials and methods: This cross-sectional study included 805 Caucasian youths with OW or OB (aged 6-18 years) recruited at seven Italian centers for the care of OW/OB. Individuals with TH out of the normal range of TH in each center were excluded. The fT3/fT4 ratio was evaluated to assess peripheral sensitivity, while TSH index (TSHI), Thyrotroph T4 Resistance Index (TT4RI), Thyroid Feedback Quantile-based Index (TFQI) and Parametric TFQI were calculated to assess central sensitivity.

Results: Youths with IGT (n =72) showed higher levels of TSH (3.08 ± 0.98 vs 2.68 ± 0.98 mIU/L, P =0.001), TSHI (3.06 ± 0.51 vs 2.85 ± 0.53, P =0.001), TT4RI (46.00 ± 17.87 vs 38.65 ± 16.27, P <0.0001), TFQI [1.00 (0.97-1.00) vs 1.00 (0.99-1.00)], P=0.034), PTFQI (0.67 ± 0.20 vs 0.60 ± 0.22, P =0.007) compared to youths without IGT (n =733), independently of centers and age. No differences were observed for fT3/fT4-ratio. The others phenotypes of prediabetes were not associated with altered sensitivity to TH. Odds ratio of IGT raised of 1-7-fold for each increase of 1 mIU/L in TSH (P =0.010), 1 unit in TSH Index (P =0.004), TT4RI (P =0.003) or PTFQI (P =0.018), independently of centers, age, and prepubertal stage.

Conclusion: IGT was associated with a reduced central sensitivity to TH in youths with OW/OB. Our finding suggests that IGT phenotype, known to be associated with an altered cardiometabolic risk profile, might also be associated with an impaired TH homeostasis in youths with OW/OB.