Association between free triiodothyronine and diabetic retinopathy: insights from a longitudinal cohort study and Mendelian randomization

In conclusion, our study demonstrated an inverse association between fT3 levels and the risk of both NPDR and PDR. Moderate fT3 levels were associated with a lower risk of DR onset or progression, particularly among patients with suboptimal glycemic control (HbA1c ≥7%) or longer diabetes duration (≥ 10 years). In older patients (≥ 55years), even relatively higher fT3 levels may be protective. MR analysis suggested a potential protective effect of elevated fT3 levels on the risk of NPDR, which was significant only in the MR Egger model.