Subclinical Hypothyroidism Is a Risk Factor for Diabetic Retinopathy in Patients with Type 2 Diabetes Mellitus

Diabetic retinopathy (DR) is one of the most common complications of diabetes. The known risk factors for microvascular complications are uncontrolled diabetes, duration of diabetes, dyslipidemia, and hypertension. In addition to these conventional risk factors, other risk factors, such as hypothyroidism have recently been suggested. Adult patients with type 2 diabetes mellitus (T2DM) were recruited. All patients were evaluated for retinopathy. Various clinical and biochemical parameters, including thyroid function tests, were assessed and compared between groups. In this study, 928 patients with (T2DM) were included. Of all patients, 376 (40.52%) had DR. In patients with retinopathy, 115 (30.58%) had proliferative and 261 (69.42%) had nonproliferative retinopathy. In patients with nonproliferative DR, 34.48%, 32.95%, and 32.57% had mild, moderate, and severe nonproliferative DR, respectively. Of all patients, 91 (9.8%) had subclinical hypothyroidism. There was a significant relationship between subclinical hypothyroidism (SCH) and DR in these patients. In patients with retinopathy, 14.4% and in patients without retinopathy, 6.7% had SCH (p<0.001). In univariate logistic regression analysis, the chance of developing DR in patients with SCH was 2.33 times higher than patients without subclinical hypothyroidism, each unit increase in the thyroid-stimulating hormone significantly increases the chance of developing DR by 13%. The present study showed that in the population of patients with (T2DM), SCH is associated with DR, regardless of the conventional risk factors.