Abstract: Objective: To study the effect of 25-hydroxyvitamin D level on incidence of diabetic nephropathy in type 2 diabetic patients by 3-year follow-up study. Methods: From June 2009 to June 2012, a total of 530 type 2 diabetic patients with normal albuminuria were recruited. The fasting blood glucose, C peptide, glycosylated hemoglobin, 25-hydroxyvitamin D, blood lipids and 24 h urinary albumin excretion rate were measured in all the patients at baseline. The study patients were divided into 3 groups based on the baseline 25-hydroxyvitamin D level. All patients were followed up for 3 years. At the end of follow-up, 24 h urine was taken to detect the urinary albumin excretion rate to determine whether there was diabetic nephropathy. The incidence of diabetic nephropathy in the three groups was analyzed at the end of 3-year follow-up. Results: After 3 years, the urinary albumin excretion rate in vitamin D deficiency group was significantly higher than that in vitamin D normal group[25.9(3.1-379.6) mg/24 h vs 18.8（2.5-103.7） mg/24 h, P<0.01]. The incidence of diabetic nephropathy in the vitamin D deficiency group was higher than those in the vitamin D normal group and vitamin D insufficient group (26.2% vs 5.3%, 26.2% vs 12.7% P<0.05). Regression analysis showed that vitamin D deficiency significantly increased the risk of diabetic nephropathy (RR=1.58, 95%CI: 1.13-2.79), and this effect remained after controlling other multiple risk factors (RR=1.23, 1.05-2.12). Conclusions: A 3-year prospective cohort study confirmes that vitamin D deficiency significantly increases the risk of diabetic nephropathy in patients with type 2 diabetes. Vitamin D deficiency is an important factor for the development and progression of diabetic nephropathy.

Key words: Vitamin D, Type 2 diabetes mellitus, Diabetic nephropathy, Urinary albumin excretion rate