Association of Vitamin D Status with Diabetic Retinopathy in Patients with Type 2 Diabetes Mellitus: A Cross-Sectional Study from Iran

Objective: Diabetic retinopathy (DR) is a major microvascular complication of type 2 diabetes mellitus (T2DM). In addition to hyperglycemia, vitamin D may influence DR via anti-inflammatory and anti-angiogenic mechanisms. This study examined the relationship between serum vitamin D levels and the presence and severity of DR, while accounting for clinical, biochemical, and lifestyle factors. 

Methods: A total of 120 patients with T2DM attending an ophthalmology clinic participated in this cross-sectional study. The presence of DR was determined through fundus photography and established DR criteria (ETDRS). Data included serum 25(OH)D, hemoglobin A1c (HbA1c), cholesterol, and clinical data. Patients were divided according to DR status as either DR or non-DR and further classified as non-proliferative diabetic retinopathy or proliferative diabetic retinopathy (PDR). 

Results: Compared to non-DR patients, those with DR had lower mean serum vitamin D levels (19.43 ± 4.50 ng/mL vs. 26.48 ± 8.99 ng/mL, P < .001). Diabetic retinopathy was associated with longer duration of diabetes and higher HbA1c and cholesterol. Patients with DR and PDR were more susceptible to vitamin D deficiency and were less likely to receive supplemental vitamin D. In a stepwise-adjusted multivariate regression model, low vitamin D and longer duration were independent predictors of DR. The risk of DR was also associated with a history of smoking and insulin therapy. 

Conclusion: Vitamin D deficiency is strongly associated with DR in Iranian patients with T2DM. Further research should clarify vitamin D’s potential as a modifiable risk factor for prevention strategies. 

Cite this article as: Zamani F, Babaei M, Heidari B, Bayani MA, Gholinia H, Rasoulinejad SA. Association of vitamin D status with diabetic retinopathy in patients with type 2 diabetes mellitus: A cross-sectional study from Iran. Endocrinol Res Pract. Published online February 6, 2026. doi: 10.5152/erp.2026.25812.