Higher free triiodothyronine concentration is associated with lower prevalence of microangiopathic complications and better metabolic control in adult euthyroid people with type 1 diabetes

Type 1 diabetes mellitus (T1DM) is a disorder of insulin deficiency but with a wide range of hormones simultaneously disturbed. The study was performed to explore relation of free triiodothyronine (FT3) with metabolic control and occurrence of microangiopathic complications. A total of 266 adult T1DM participants [56% men; 32 (interquartile range, IQR: 25-39) years and disease duration 13 (IQR: 8-19) years] in euthyroid state with negative history for hypothyroidism were included to the study. Participants were screened for thyroid-stimulating hormone (TSH), free thyroxine (FT4) and FT3. Moreover, microangiopathic complications (retinopathy, diabetic kidney disease, peripheral and autonomic neuropathy), markers of metabolic control such as glycated hemoglobin (HbA(1c)) were evaluated. A total of 114 (42.9%) people had diagnosed at least one microangiopathic complication. In multivariable linear regression higher HbA(1c) was statistically significant independent predictor of lower FT3 (beta = -0.25; p < 0.0001) after adjustment for sex, T1DM duration, HbA(1c), waist-to-hip ratio (WHR) (R (2) = 0.15, p < 0.0001). Higher FT3 was simultaneously a predictor of lower prevalence of microangiopathy in multivariate logistic regression analysis (odds ratio, 0.51; 95% confidence interval, 0.27-0.98; p = 0.04) after an adjustment for: age, hypertension, HbA(1c), WHR and total cholesterol (TC). FT3 as tissue active hormone plays a clinically important role in T1DM people. The higher FT3 concentration is related to the lower prevalence of microangiopathy and better metabolic control of the disease in adult euthyroid people with T1DM.