Vitamin D Deficiency as a Potential Biomarker of Diabetic Retinopathy in Patients with Type 2 Diabetes Mellitus

Purpose: Diabetic retinopathy (DR) is a leading cause of vision loss globally, and vitamin D deficiency has been implicated in its pathogenesis. This study aimed to investigate the association between serum 25-hydroxyvitamin D (25(OH)D) levels and DR in patients with type 2 diabetes mellitus (T2DM). Patients and methods: This comparative cross-sectional study included 120 Yemeni male participants aged 40–60 years. Participants were divided into four groups: 30 healthy controls, 30 T2DM patients without retinopathy (DWR), 30 T2DM patients with non-proliferative diabetic retinopathy (NPDR), and 30 T2DM patients with proliferative diabetic retinopathy (PDR). Serum 25(OH)D, HbA1c, fasting blood glucose (FBS), lipid profile, and intraocular pressure (IOP) were measured. Data were analyzed using SPSS version 22, with p < 0.05 considered statistically significant. Results: Serum 25(OH)D levels were significantly lower in the PDR group (10.6 ± 2.1 ng/mL) than in the NPDR group (20.5 ± 2.8 ng/mL), DWR group (26.4 ± 1.9 ng/mL), and control group (34.2 ± 3.9 ng/mL) (p < 0.0001). Approximately 66.6% (n=60) of DR patients had 25(OH)D deficiency (<20 ng/mL). HbA1c, FBS, total cholesterol, LDL-c, and triglycerides were significantly higher in DR patients, whereas HDL-c levels were significantly lower (p < 0.05). IOP was also significantly higher in DR patients compared with DWR and controls (p < 0.0001). A significant negative correlation was observed between serum 25(OH)D levels and HbA1c, FBS, total cholesterol, LDL-c, triglycerides, BMI, and IOP, whereas a positive correlation was observed with HDL-c (p < 0.0001). Conclusion: Serum 25(OH)D levels were significantly lower in patients with diabetic retinopathy than in healthy controls and patients with diabetes without retinopathy. Vitamin D deficiency is associated with poor glycemic control, dyslipidemia, and increased intraocular pressure, suggesting a potential role for vitamin D as a biomarker of DR. Further research is needed to evaluate the therapeutic potential of vitamin D supplementation in the prevention or management of DR.