In 2013, half of Americans reported taking vitamins; sales of which total at least $28 billion a year. At a forum at the American Association for Cancer Research (AACR) Annual Meeting 2015 by University of Colorado Cancer Center, researcher Tim Byers, MD, MPH, describes research revealing that over-the-counter supplements may actually increase cancer risk when more than the recommended daily amount is taken. One trial looking at beta carotene supplements found that exceeding the recommended dosage increased the risk for developing both lung cancer and heart disease by 20 percent. Another trial found that folic acid, which was thought to help reduce the number of polyps in a colon, actually increased the number, according to a press statement for the study. Byers says that people can get all the vitamins and minerals the body needs by eating healthy meals – and that many adults who take vitamins quite possibly don’t need them. And that too much can do more harm than good.
http://www.coloradocancerblogs.org/dietary-supplements-shown-to-increase-cancer-risk/