Objective: To explore the effects of thyroid hormone on islet β cell function among type 2 diabetics with normal thyroid function.
Methods: A total of 266 type 2 diabetics with normal thyroid function were recruited. Their clinical, biochemical parameters and thyroid related hormones were measured. And acute insulin response (AIR) was examined by arginine stimulating test.
Results: The serum levels of triiodothyronine (T3) ((1.49 ± 0.03), (1.59 ± 0.03), (1.70 ± 0.04) µmol/L) and free triiodothyronine (FT3) ((4.01 ± 0.08), (4.37 ± 0.09), (4.44 ± 0.07) pmol/L) were significantly different among tertile groups of AIR (both P < 0.01) while those of thyroxine (T4), free thyroxine (FT4) and thyroid stimulating hormone (TSH) showed no significant differences among tertile groups of AIR (all P > 0.05). A significant positive correlation existed between lnAIR and T3, FT3 (r = 0.303, 0.302, both P < 0.01). T4 and FT4 were not correlated with lnAIR (both P>0.05). AIR was significantly different among tertile groups of T3 ((2.38 ± 0. 12), (2.64 ± 0.12) and (3.03 ± 0.10) mU/L) and FT3 ((2.34 ± 0.11), (2.69 ± 0.13), (2.99 ± 0.10) mU/L, P < 0.01). AIR were not significantly different among tertile groups of T4, FT4 and TSH (all P > 0.05). Multivariate linear regression demonstrated that T3 and FT3 level were independently associated with AIR (β = 0.686, 95% CI 0.289-0.884, P = 0.001, β = 0.296, 95% CI 0.125-0.467, P = 0.01).
Conclusions: Significant positive associations exist between serum T3, FT3 and AIR in type 2 diabetics with normal thyroid function. Serum T3 and FT3 may be the independent risk factors of predicting islet beta cell function in type 2 diabetics with normal thyroid function. However, it remains to be determined whether or not normal physiological concentrations of T3 and FT3 are protective factors for islet β cell functions among type 2 diabetics.