Association of thyroid function within the normal range with glycemic control and cardiovascular risk in type 1 diabetes

Abstract

Purpose: Changes in thyroid hormone (TH) levels, even within the normal range, influence cardiometabolic health. In type 1 diabetes (T1D), optimal control of glucose levels and cardiovascular risk is crucial to prevent complications. We aim to explore the association of TH within normal range with cardiometabolic profile in T1D. Methods: Cross-sectional analysis including adult patients with T1D followed at our Endocrinology Department between 2022-2024. We excluded patients with TSH or fT4 outside the reference range. We analyzed the associations between TH (TSH, fT4, fT3 and fT3/fT4 ratio) and glycemic, anthropometric, and cardiometabolic parameters, using linear regression models unadjusted and adjusted for relevant variables. Restricted cubic splines between TH and glycemic control parameters were performed to assess non-linear associations. Results: We included 296 patients (median age 35 [25.0, 47.0] years, 42.6% female). Those with TSH in the middle tertile had a higher time in range and a lower time above range. Waist circumference (WC) and body mass index (BMI) were negatively associated with fT4, and positively with fT3 and Ft3/fT4 ratio. Estimated glomerular filtration rate (eGFR) was negatively associated with TSH and fT4, and positively with fT3 and fT3/fT4 ratio. Conclusions: Variations in TH within the normal range were associated with glycemic control and cardiovascular risk in T1D. Patients with low-normal and high-normal TSH had a poorer glycemic control. Patients with lower fT4 and higher fT3 and fT3/fT4 ratio had higher BMI and WC. Finally, those with higher fT4 and lower fT3 and fT3/fT4 ratio presented a worse kidney function.