# Predictive Effect of FT3 Within the Euthyroid Range on HDL‐C in Patients With Type 2 Diabetes: A Cross‐Sectional Analysis of Inpatients in China

## TL;DR

This study finds that free triiodothyronine (FT3) levels within a specific range are linked to stable HDL cholesterol in type 2 diabetes patients, potentially helping reduce cardiovascular risk.

## Contribution

The study identifies a nonlinear relationship and optimal FT3 range for cardiovascular benefits in T2DM patients.

## Key findings

- FT3 and HDL-C are negatively correlated within the euthyroid range.
- A nonlinear relationship exists with an inflection point at 3.48 pmol/L FT3.
- Maintaining FT3 between 2.76–3.48 pmol/L may benefit cardiovascular health in T2DM patients.

## Abstract

Evidence for assessing the relationship between free triiodothyronine (FT3) and high‐density lipoprotein cholesterol (HDL‐C) remains limited. Therefore, the purpose of our study is to evaluate the relationship between FT3 and HDL‐C in patients with type 2 diabetes.

From June 2022 to October 2023, 3011 patients with normal thyroid function and diagnosed with type 2 diabetes mellitus (T2DM) were collected continuously and non‐selectively in a Chinese hospital. Then, we used a logistic regression model to explore the relationship between FT3 and HDL‐C. Smooth curve fitting is used to identify the nonlinear relationship between FT3 and HDL‐C.

After adjusting for the influence of relevant factors, FT3 and HDL‐C were negatively correlated −0.02 (−0.04, −0.00; p = 0.0162). There is also a nonlinear relationship between FT3 and HDL‐C, with an inflection point of 3.48 pmol/L for FT3 (P for log‐ likelihood ratio test = 0.044).

This study shows that there is a negative correlation and nonlinear relationship between FT3 and HDL‐C in the Chinese population with diabetes. When FT3 is between 2.76–3.48 pmol/L, HDL‐C tends to a stable state; When FT3 is between 3.48–6.45 pmol/L, HDL‐C decreases with the increase of FT3 concentration (According to the reference range used by our hospital, the normal value of serum FT3 is 2.76–6.45 pmol/L). These findings suggest that maintaining FT3 within the range of 2.76 to 3.48 pmol/L may be most beneficial for mitigating the progression of cardiovascular disease in patients with T2DM.

Our research is important for identifying the optimal FT3 range to delay the progression of cardiovascular disease in patients with T2DM. These findings provide valuable insights to guide clinicians in preventing and managing cardiovascular disease in this population.