[Effects of thyroid hormone on islet β cell function among type 2 diabetics with normal thyroid function]

To explore the effects of thyroid hormone on islet β cell function among type 2 diabetics with normal thyroid function.

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.

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).

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.