Supplementary Material for: Vitamin D Treatment and Mortality in Chronic Kidney Disease: A Systematic Review and Meta-Analysis

Background/Aims: Hypovitaminosis D has been associated with an increased cardiovascular mortality in the general population and in patients with chronic kidney disease (CKD). Still, whether prescribing vitamin D reduces the risk of mortality in renal patients remains controversial. Methods: We searched PubMed, ClinicalTrials.gov and the Cochrane Library for long-term longitudinal studies comparing vitamin D compounds (25-hydroxyvitamin D, 1,25-dihydroxyvitamin D and synthetic derivatives) to placebo or no treatment in renal patients, and which evaluated mortality, to perform a meta-analysis. Data concerning study quality, population and effect size were extracted independently by two investigators using predefined forms. Results: Fourteen observational studies (194,932 patients) met all eligibility criteria. Most studies were performed in hemodialysis patients and all used calcitriol or synthetic analogues. In a random effects meta-analysis, receiving any vitamin D therapy significantly reduced the risk of all-cause mortality (relative risk 0.73, 95% CI 0.65-0.82). The relative risk of death was 0.72 (95% CI 0.65-0.80) after 3 years of therapy and 0.67 (95% CI 0.45-0.98) after 5 years. In meta-regression, the risk reduction was shown to be greater in patients with higher parathyroid hormone serum levels (p = 0.01). The risk of cardiovascular mortality was also significantly reduced in patients receiving any vitamin D derivative (relative risk 0.63, 95% CI 0.44-0.92). Conclusion: Therapies with 1,25-dihydroxyvitamin D and analogues are associated with reduced mortality in CKD patients, and particularly in those suffering from secondary hyperparathyroidism. These results, based on observational evidence, are supportive of prescribing vitamin D therapies to CKD patients, while respecting good practice guidelines.