webmd.com: Getting Too Much of Vitamins And Minerals
The health consequences of going overboard.
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 stomachcramps. Too much selenium could lead to hair loss, gastrointestinal upset, fatigue, and mild nerve damage.
While most people aren't getting megadoses, if you eat a fortified cereal at breakfast, grab an energy bar between meals, have enriched pasta for dinner, and take a daily supplement, you could easily be over the recommended daily intake of a host of nutrients.
Here's what you need to know to avoid overdoing it.