Sex-influenced association between free triiodothyronine levels and poor glycemic control in euthyroid patients with type 2 diabetes mellitus

Abstract Objective The study investigated the association between free triiodothyronine (FT3) and poor glycemic control with different definitions in euthyroid patients with type 2 diabetes mellitus (T2DM). Methods This was a cross-sectional study which included 2,172 patients from National Metabolic Management Center in Ruijin Hospital. The association between thyroid function and glycated hemoglobin A1c (HbA1c) was determined by multiple liner regression models. The association between FT3 and poor glycemic control was further determined by binary logistic regression models. Two definitions of poor glycemic control (HbA1c ≥ 7% and HbA1c ≥ 8%) were applied when we analyzed the association. Results Prevalence of HbA1c ≥ 7% and HbA1c ≥ 8% were 63.8% and 39.3%, respectively. After adjusting for confounding factors, FT3, rather than free tetraiodothyronine (FT4) or thyroid stimulating hormone (TSH), was independently associated with HbA1c (β = -0.104, P = 0.002). Further analysis after gender stratification showed that the association was only found in males (β = -0.164, P Conclusions FT3 in the reference range was significantly associated with reduced risk of HbA1c ≥ 8% in males, independent of traditional risk factors for poor glycemic control.