Periodically nutrition studies are promoted which suggest that vitamin supplements are harmful. These are widely promoted in spite of the fact that most studies show considerable benefit. A study published in 2012 suggests that nutritional studies can be confusing because sick people who do not feel well are more likely to supplement their diets. In this study antioxidant supplement users significantly reduced their risk of cancer and all cause mortality (death from all causes). The researchers noted, however, that nonusers who began supplementing during follow-up had increased risk of cancer and death. They suggested that the use of supplements could confound the conclusions in nutrition studies. The following quote is from the research paper.
"Based on limited numbers of users and cases, this cohort study suggests that supplementation of antioxidant vitamins might possibly reduce cancer and all-cause mortality. The significantly increased risks of cancer and all-cause mortality among baseline non-users who started taking supplements during follow-up may suggest a 'sick-user effect,' which researchers should be cautious of in future observational studies."
Heaney writes in the Journal of Nutrition that the randomized controlled trial which is the standard in medicine is not really appropriate for the study of nutrients. He wrote, "To sum up, I think that there would be general agreement to the effect that nutrition is important, despite the fact that the still growing number of failed trials of individual nutrients might suggest that no nutrient actually made much of a difference, a conclusion that is absurd on its face and ought to have alerted us to the possibility that there was something wrong with how we were investigating the matter. To provide the proof needed to sustain revised intake recommendations, we shall have to find a design better suited to nutrients than the randomized controlled trial as currently implemented."
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