Nowadays, everything from bottled water to orange juice seems to have souped-up levels of vitamins and minerals in it. That may sound like a way to help cover your nutritional bases, especially if your diet is less than stellar. But routinely getting an overload of vitamins and minerals can hurt you. Too much vitamin C or zinc could cause nausea, diarrhea, and stomach cramps. Too much selenium could lead to hair loss, gastrointestinal upset, fatigue, and mild nerve damage.