Vitamin D supplementation for the improvement of vascular function in patients with chronic kidney disease: a meta-analysis of randomized controlled trials

BackgroundThe efficacy of vitamin D on vascular function remains controversial in chronic kidney disease (CKD) patients. The aim of the present work was to perform a meta-analysis of randomized controlled trials to evaluate the efficacy of vitamin D on vascular function in CKD patients.MethodsWe searched Medline, the Cochrane Central Register of Controlled Trials, Embase, the Science Citation Index, and clinical trial registries for randomized controlled trials comparing vitamin D with a placebo in CKD patients.ResultsWe included seven trials. For flow-mediated dilation (FMD), there was no significant difference between the two groups (WMD 1.66%; 95% CI -0.2 to 3.51, p=0.08; with significant heterogeneity, p<0.0001, I-2=89%). We conducted a subgroup analysis. In the cholecalciferol group, compared with the placebo group, cholecalciferol significantly increased FMD (WMD 5.49%; 95% CI 4.36-6.62, p<0.0001). In the 2ug paricalcitol group, compared with the placebo group, paricalcitol significantly increased FMD (WMD 2.09%; 95% CI 1.28-2.9, p<0.0001; without significant heterogeneity, p=0.47, I-2=0%). In the 1 ug paricalcitol group, there was no significant difference between the two groups. For pulse wave velocity (PWV), vitamin D significantly decreased PWV compared with the placebo (WMD -0.93m/s; 95% CI -1.71 to -0.15, p=0.02; without significant heterogeneity, p=0.14, I-2=45%). For calcium (Ca) and parathyroid hormone (PTH), there was a significant difference between the vitamin D group and the placebo group. For 25-hydroxyvitamin D [25(OH)D], there was a significant difference between the inactive vitamin D group and the placebo group. For phosphorus (P), systolic blood pressure (SBP), and diastolic blood pressure (DBP), there were no significant differences between the two groups.ConclusionsWe speculate that vitamin D might be able to improve vascular function in CKD patients. The effect of vitamin D might be associated with its doses and earlier stages of the disease might respond better to vitamin D. Furthermore, trials with larger populations and longer durations are needed in order to provide more reliable evidence.