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The use of dietary supplement products is common in the United States. The National Health and Nutrition Examination Survey, conducted from 1999 through 2012, showed that more than half the adults in the United States consumed dietary supplements.1 In the past decade, the numbers of persons who supplemented their diets with fish oil increased by a factor of 10 and with vitamin D by a factor of 4.1 But any long-term health benefits from these products remain in doubt. Hence, the results from the Vitamin D and Omega-3 Trial (VITAL), a randomized, double-blind, placebo-controlled trial (with a two-by-two factorial design) . . .