What if you could prevent cancer and heart disease by simply buying a few items off the grocery shelf? Sound crazy? Well, apparently many Americans don't think so. More than 40% of us take vitamins and other supplements, driving a $30 billion a year business that shows no sign of slowing down. But how safe is it to play your own doctor? Practitioners of both conventional and integrative medicine debate the pros and cons of nutritional supplements on this episode of Second Opinion.