Vitamins are healthy, sure―but there is a risk of overloading. Here's what you need to know.

Fish with broccoli, beans, nuts and an orange
Credit: Anita Calero

Getting too many vitamins from food is almost unheard-of, but if you're taking individual supplements as a backup, use caution. "At megadoses of up to 10 times what's recommended, some nutrients behave very much like drugs," says Lora Sporny, a professor of nutrition at Columbia University.

Some examples: Too much calcium may inhibit iron absorption. Too much vitamin A may interfere with vitamin D function, leading to bone fractures. And vitamin E taken in amounts over 20 times the RDA can have an anticlotting effect―potentially dangerous if you're already taking aspirin or blood thinners. If you are concerned about your vitamin intake, talk to your doctor before you start on any supplements.