Vitamin D status and all-cause mortality in patients with chronic kidney disease: A systematic review and dose-response meta-analysis.

Context: Prevalence of vitamin D deficiency is high in patients with chronic kidney disease. Less attention has been paid to measurement and correction of serum level of 25(OH)D in these patients. Objective: We examined the association between different levels of serum 25(OH)D and risk of all-cause mortality in patients with chronic kidney disease. Data sources: Systematic search were done using MedLine and EMBASE from inception up to November 2016. Reference lists of all relevant articles and reviews also were searched. Study selection: Prospective or retrospective cohort studies that reported risk estimates of all-cause mortality for three or more categories of serum 25(OH)D in patients with chronic kidney disease were selected. Studies that reported results as continuously also were included. Two independent investigators screened and selected the articles. Of 1281 identified studies, 13 prospective cohorts, two retrospective cohorts and one nested case-control study with 17053 patients and 7517 incident death were included. Data Extraction: Two independent authors extracted data from included studies. Any discrepancies were resolved through consensus. Data Synthesis: Reported risk estimates were combined using a random-effects model. Summary risk estimates of all-cause mortality were1.63 (95%CI: 1.32, 1.94) for severe deficiency (<10 ng/ml), 1.22 (95%CI: 1.09, 1.35) for mild deficiency (10-20 ng/ml) and 1.12 (95%CI: 1.06, 1.18) for insufficiency (20-30 ng/ml). Results were more evident in dialysis dependent patients. 10 ng/ml increment in serum 25(OH)D was associated with 21% reduction in the risk of overall mortality (RR: 0.79, 95%CI: 0.70, 0.87).Lower risk of all-cause mortality was observed at serum 25(OH)D about 25 to 30 ng/ml. Dialysis treatment was one of the sources of variation between studies. Conclusions: Higher levels of serum 25(OH) D were associated with lower risk of all-cause mortality in patients with chronic kidney disease, but concerning serum levels more than 35 ng/mL we have no conclusive evidence.