Thyroid hormones have a specific effect on glucose-induced insulin secretion from the pancreas.We aimed to investigate the association between euthyroid hormones and islet betacell function in general population and non-treated type 2 diabetes mellitus(T2DM)patients.A total of 5089 euthyroid participants(including 4601 general population and 488 non-treated T2DM patients)were identified from a cross-sectional survey on the prevalence of metabolic diseases and risk factors in East China from February 2014 to June 2016.Anthropometric indices,biochemical parameters,and thyroid hormones were measured.Compared with general population,non-treated T2DM patients exhibited higher total thyroxine(TT4)and free thyroxine(FT4)levels but lower ratio of free triiodothyronine(T3):T4(P<0.01).HOMA-βhad prominently negative correlation with FT4 and positive relationship with free T3:T4 in both groups even after adjusting for age,body mass index(BMI)and smoking.When analyzed by quartiles of FT4 or free T3:T4,there were significantly decreased trend of HOMA-β going with the higher FT4 and lower free T3:T4 in both groups.Linear regression analysis showed that FT4 but not FT3 and free T3:T4 was negatively associated with HOMA-β no matter in general population or T2DM patients,which was independent of age,BMI,smoking,hypertension and lipid profiles.FT4 is independently and negatively associated with islet beta-cell function in euthyroid subjects.Thyroid hormone even in reference range could play an important role in the function of pancreatic islets.
