A study published in the Journal of the American Medical Association (JAMA) reports that high intakes of folic acid and vitamin B12 may increase the risk of cancer, deaths from cancer, and mortality from all causes in people with ischemic heart disease, in which reduced blood supply to the heart causes chest pain and difficulty exercising. The study’s surprising results have spurred a flurry of concern from some and backlash from others, as we try to gain a better understanding of the real risks of supplementing with or fortifying foods with these essential vitamins.