Vitamin D and risk of cause specific death: systematic review and meta-analysis of observational cohort and randomised intervention studies

To evaluate the extent to which circulating biomarker and supplements of vitamin D are associated with mortality from cardiovascular, cancer, or other conditions, under various circumstances.

Systematic review and meta-analysis of observational studies and randomised controlled trials. DATA SOURCES: Medline, Embase, Cochrane Library, and reference lists of relevant studies to August 2013; correspondance with investigators. STUDY SELECTION: Observational cohort studies and randomised controlled trials in adults, which reported associations between vitamin D (measured as circulating 25-hydroxyvitamin D concentration or vitamin D supplement given singly) and cause specific mortality outcomes. DATA EXTRACTION: Data were extracted by two independent investigators, and a consensus was reached with involvement of a third. Study specific relative risks from 73 cohort studies (849,412 participants) and 22 randomised controlled trials (vitamin D given alone versus placebo or no treatment; 30,716 participants) were meta-analysed using random effects models and were grouped by study and population characteristics.