Taking excessively high doses of some vitamins and minerals can backfire—or be a complete waste of your time (and money).Reviewed by Dietitian Kelly Plowe, M.S., RDCredit: Getty Images. EatingWell design.Key PointsDietary supplements shouldn't be taken to reduce your cancer risk.Experts encourage getting nutrients from foods like fruit, veggies and whole grains instead.Consider lifestyle changes like limiting alcohol and getting regular exercise…