Low Vitamin D Levels are Associated with Vascular Endothelial Dysfunction in Patients with Type 2 Diabetes: A Retrospective Study

Background: The aim of this study was to determine the association between serum 25-hydroxyvitamin D (25(OH)D) levels and vascular endothelial function in patients with type 2 diabetes (T2D).Methods: This retrospective study included 113 T2D patients who were admitted for in-hospital diabetes educational program and underwent measurements of serum 25(OH)D levels and reactive hyperemia index (RHI). The primary endpoint was the association between serum 25(OH)D levels and RHI in T2D patients.Results: Serum 25(OH)D levels correlated significantly with RHI in T2D patients (r=0.285, p=0.002). Receiver operating characteristic (ROC) curve analysis showed that serum 25(OH)D level of 16.5 ng/mL is the optimal cut-off level for predicting vascular endothelial dysfunction (RHI<1.67), with a sensitivity of 68.5%, specificity of 67.9%, and area under the ROC curve (AUC) of 0.668 (95% confidence interval [CI]: 0.566–0.770, p=0.002). The mean RHI was significantly lower (1.70±0.54) in patients with low 25(OH)D levels (n=56, 25(OH)D levels <16.5 ng/mL) than that (1.99±0.58 vs.; p<0.001) of patients with high 25(OH)D levels (n=57, 25(OH)D level >16.5 ng/mL). The proportion of patients with RHI<1.67 was also higher in the low 25(OH)D group than in the high 25(OH)D group (38% vs. 18%; p<0.001). Multivariate logistic regression analysis identified serum 25(OH)D levels <16.5 ng/mL was associated with increased odds of RHI <1.67 (odds ratio 4.598, 95% CI 1.961–10.783, p <0.001).Conclusions: The results demonstrated the association of serum 25(OH)D levels with endothelial function in T2D patients and identified serum 25(OH)D level of <16.5 ng/mL as a predictor of vascular endothelial dysfunction. Serum 25(OH)D level is a potentially useful marker of vascular endothelial dysfunction in T2D patients.