Vitamin D deficiency increases the risk of retinopathy in Chinese patients with Type 2 diabetes

Aims To investigate the relationship between vitamin D deficiency and diabetic retinopathy. Methods In total, 1520 patients with Type 2 diabetes were recruited and divided into three groups according to their fundus oculi results: no diabetic retinopathy ( n =  625, 41.12%); non‐sight‐threatening diabetic retinopathy ( n =  562, 36.97%); and sight‐threatening diabetic retinopathy ( n =  333, 21.91%). Vitamin D deficiency was defined as a serum circulating 25–hydroxyvitamin D level < 20 ng/ml. Clinical characteristics and biochemical parameters were detected and compared. Results The patients with sight‐threatening diabetic retinopathy had significantly lower serum 25–hydroxyvitamin D concentrations and higher prevalence of vitamin D deficiency than other two groups (all P  < 0.05). In addition, there was a downward trend in average 25–hydroxyvitamin D level with the increased stages of diabetic retinopathy ( P  < 0.01). The prevalence of diabetic retinopathy and sight‐threatening diabetic retinopathy in patients with vitamin D deficiency was also higher than in those without vitamin D deficiency (both P  < 0.01). After adjusting for all potential confounders, vitamin D deficiency was still associated with increased risk of diabetic retinopathy (odds ratio 1.93) and sight‐threatening diabetic retinopathy (odds ratio 2.42) (both P  < 0.01). Logistical regression analysis further revealed that vitamin D deficiency was an independent risk factor for diabetic retinopathy (β  =  0.66) and sight‐threatening diabetic retinopathy (β  =  0.93) (both P  < 0.01). ROC analysis indicated that a serum 25–hydroxyvitamin D level < 15.57 ng/ml suggested the occurrence of sight‐threatening diabetic retinopathy (odds ratio 2.38, P < 0 .01). Conclusions Vitamin D deficiency is an independent risk factor for diabetic retinopathy and sight‐threatening diabetic retinopathy. The prevalence of sight‐threatening diabetic retinopathy doubles when the serum 25–hydroxyvitamin D level is < 15.57 ng/ml.