Euthyroid type 2 diabetes patients with higher thyroid-stimulating hormone (TSH) levels within the normal range are at a higher risk of developing diabetic retinopathy (DR). Suboptimal glycemic control, as indicated by lower time in range (TIR) further compounded the risk. These findings were recently published in the journal Diabetes/Metabolism Research and Reviews.¹ 

A cross-sectional study was conducted by researchers from China involving 2740 patients with type 2 diabetes, aged 61 years (median), who had been hospitalized in Shanghai Sixth Peoples Hospital. Nearly two-thirds of the participants were men. All participants were euthyroid at the time of their enrolment. Based on the severity of the diabetic retinopathy as assessed through fundus photography, the study subjects were segregated into groups: no diabetic retinopathy (DR), mild nonproliferative diabetic retinopathy (NPDR), moderate NPDR or severe NPDR or PDR.

Results showed that 794 (29%) of participants were diagnosed with DR. TSH levels were considerably higher among patients with DR, while free triiodothyronine (FT3) levels were significantly lower in patients with DR than those without DR. Free thyroxine (FT4), thyroglobulin antibody (TGAb) and thyroid peroxidase antibody (TPOAb) were comparable between the two groups.

Patients with the highest TSH levels were more prone to developing DR with adjusted odds ratio (aOR) of 1.48 than those without DR. After adjustment for confounders, the probability of developing DR was higher among the participants in the highest tertile of TSH. The aOR for mild NPDR was 1.39, for moderate NPDR, the aOR was 1.84 and for severe NPDR or PDR, the aOR was 1.64 compared to patients in the lowest TSH tertile.

The prevalence of DR was ~24% among the participants with TIR >70%, measured via continuous glucose monitoring (CGM). Those with TSH in the highest tertile were 1.54 times more likely to develop DR vs lowest tertile group.

Participants were further divided into six categories based on the TIR (>70%, ≤70%) and TSH tertiles (T1, T2 and T3). Compared to the reference group of patients with TIR >70% and the lowest TSH tertile, those with TIR of 70% or less and in the highest TSH tertile category were most likely to develop DR with nearly 2-folds increase in the risk after multivariate adjustments (OR 1.96).

According to the authors, theirs is the first study to examine the effect of glycemic control and thyroid profile on the risk of DR. This study shows that even patients with well-controlled diabetes (TIR >70%) but with higher TSH levels were also at a higher risk of DR. The risk was further increased in patients with higher TSH levels and lower TIR (suboptimal glycemic control). “More attention should be paid to the potential effects of both TSH and time in range for better management of diabetic retinopathy,” write the authors.

Reference

1. Wang Y, et al. Association of thyroid stimulating hormone and time in range with risk of diabetic retinopathy in euthyroid type 2 diabetes. Diabetes Metab Res Rev. 2023 Mar 25;e3639. doi: 10.1002/dmrr.3639.