Update on the Vitamin D and OmegA-3 trial (VITAL).

Despite continued appreciation of the potential role of vitamin D and omega-3 fatty acids in the prevention of cancer and cardiovascular disease (CVD), there remain no completed large-scale, randomized trials of these agents for the primary prevention of cancer or CVD in a population that has not been selected on the basis of elevated risk. The VITamin D and OmegA-3 TriaL (VITAL) is a 2×2 factorial randomized, double-blind, placebo-controlled trial of the benefits and risks of vitamin D (vitamin D3 [cholecalciferol], 2000 IU/d) and marine omega-3 fatty acids (Omacor(®) fish oil, a 1 g/d) in the primary prevention of cancer and CVD among 25,875 men and women, aged ≥50 and ≥55 years, respectively. Randomization began in November 2011 and was completed in March 2014. This report will describe the rationale for the trial and currently available randomized trial data, summarize related ongoing large-scale trials, and provide a brief overview of study design, and an update on randomization milestones, racial/ethnic diversity, biorepository activities, in-depth phenotyping of a subcohort, and ancillary studies.