 The VITamin D and OmegA-3 TriaL VITAL; NCT 01169259 is an ongoing randomized clinical trial in 25,875 U.S. men and women investigating whether taking daily dietary supplements of vitamin D3 2000 IU or omega-3 fatty acids Omacor fish oil, 1 gram reduces the risk of developing cancer, heart disease, and stroke in people who do not have a prior history of these illnesses. 