Nutritional vitamin D supplementation and health-related outcomes in hemodialysis patients: a protocol for a systematic review and meta-analysis

BACKGROUND: The prevalence of vitamin D deficiency in hemodialysis patients is high. While most hemodialysis patients are treated with activated vitamin D (1,25[OH](2)D) to prevent renal osteodystrophy, clinical practices of the screening and treatment of 25(OH)(2)D deficiency are highly variable. It is unclear if nutritional vitamin D supplementation with D2 or D3 provides an additional clinical benefit beyond that provided by activated vitamin D treatment in this population. METHODS/DESIGN: We will conduct a systematic review of nutritional vitamin D (D2/D3) supplementation and health-related outcomes in hemodialysis patients according to Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. The primary objective is to assess the impact of nutritional vitamin D supplementation on clinical outcomes relevant in hemodialysis patients, such as mortality, cardiovascular events, infections, and fractures. Secondary outcomes will include anemia, hyperparathyroidism, medication use (erythrocyte-stimulating agents, activated vitamin D), and quality of life. We will search MEDLINE, Scopus, Web of Science, and ClinicalTrials.gov for randomized, controlled trials of nutritional vitamin D supplementation (ergocalciferol/D2 or cholecalciferol/D3) in chronic hemodialysis patients. The Cochrane Risk Assessment Tool will be used to assess the quality of eligible studies. We will perform meta-analyses using standard techniques for the outcomes listed above if pooling is deemed appropriate/sufficient. The results of this systematic review may highlight gaps in our knowledge of the relevance of nutritional vitamin D in end-stage renal disease, allowing for the informed design of clinical trials assessing the impact of nutritional vitamin D therapy in the hemodialysis population in the future. SYSTEMATIC REVIEW REGISTRATION: PROSPERO CRD42014013931