Effects of vitamin D on inflammatory state in patients with chronic kidney disease: A controversial issue

Background The anti-inflammatory effect of vitamin D in patients with chronic kidney disease (CKD) remains controversial. This study aimed to conduct a meta-analysis of randomized controlled trials to assess the anti-inflammatory effects of vitamin D in patients with CKD. Methods We searched Embase, Science Citation Index, Medline, Cochrane Central Register of Controlled Trials, and Clinical Trial Registries for randomized controlled trials that comparing vitamin D with control groups for inflammatory markers in patients with CKD. Subgroup analysis was performed based on treatment duration (short-term treatment, long-term treatment), type of patients (predialysis CKD, dialysis, kidney transplant), 25(OH)D levels (25(OH)D deficiency or normal 25(OH)D), and methods of C-reactive protein (CRP) test (standard CRP test or high-sensitivity CRP [hs-CRP] test). Results Eighteen trials with 1834 patients were included in the present study. There were no significant differences between the vitamin D group and control group for CRP (WMD, -0.3 mg/L; 95% CI, -0.81 to 0.22, p = 0.26, I-2 = 62%), interleukin-6 (IL-6) (WMD, -1.07 pg/ml; 95% CI, -2.44 to 0.30, p = 0.12, I-2 = 52%), and tumor necrosis factor-alpha (TNF-alpha) (WMD, -0.00 pg/ml; 95% CI, -0.36 to 0.35, p = 0.99, I-2 = 0%) in patients with CKD. Subgroup analysis showed vitamin D can improve hs-CRP, but not CRP. The rest of subgroups showed that no significant differences were observed between the vitamin D group and control group based on 25(OH)D levels, treatment duration, and predialysis CKD or dialysis patients. Conclusion This meta-analysis demonstrates that vitamin D supplementation does not have anti-inflammatory effects in CKD patients. Well-designed randomized controlled trials with large samples are required to confirm this conclusion. It is still needed to find an effective treatment for inflammatory state in CKD.