The NIH-funded Vitamin D and Omega-3 Trial (VITAL) tracks 25,874 men and women across the U.S. over five years, investigating whether taking daily dietary supplements of vitamin D3 (2000 IU) or omega-3 fatty acids (Omacor® fish oil, 1 gram) reduces the risk for developing cancer, heart disease, and stroke in people who do not have a prior history of these illnesses. The trial is scheduled to end October 2017.

Research on the health effects of vitamin D, which humans primarily obtain from exposure to sunlight, has yielded mixed results, with strong claims being made by both advocates and skeptics. Some studies show inverse correlation between vitamin D levels and a range of diseases including cancer and diabetes; others indicate no significant connection. The health effects of omega-3 fatty acids are similarly uncertain. Since the 1970s, fish oil supplements (a common dietary source of omega-3 fatty acids) have been linked to increased cardiovascular health and a lower risk of heart disease and stroke, but most large clinical trials show no notable benefits. VITAL’s research leaders propose that the study’s size, scope, and rigor will more clearly determine the health effects of vitamin D and omega-3 supplements.

Will the results of the VITAL study support a connection between daily supplements of vitamin D3 and/or omega-3 fatty acids and decreased risk of cancer, heart disease, and stroke in people with no prior history of these illnesses?

A positive resolution holds if the results of the VITAL study, published after the study's close in October 2017, show that a daily supplement of either 2,000 IU of vitamin D or 1 gram of fish oil reduces the risk of stroke, cancer, and/or heart disease compared with a placebo, with a statistical significance of 95% or greater.