Nutritional Supplements: Taking Too Many Vitamins? (cont.)

In fact, many people don't know what they're taking, Rosenbloom says. "They're picking up OJ at the store, and they don't know what's in it -- is it calcium-fortified, they don't know. People are taking vitamin C supplements but don't know how much."

A Tidbit of Data

A couple of years ago, the Institute of Medicine issued a report listing "tolerable upper intake level" for all vitamins and minerals -- the maximum safe amount that anyone should take.

Vitamin A

The upper tolerable limit for adults is 10,000 IU for vitamin A. You get it from animal foods, fish, and dairy products. Also, beta-carotene (from orange and yellow veggies) gets converted to vitamin A in the body. "But the body is smart enough that it doesn't convert all that to vitamin A," Rosenbloom explains.

If you're taking a multivitamin that contains 5,000 IU, plus getting A-fortified foods in your diet, plus eating foods that contain vitamin A, you're probably OK. "It's the supplements we worry about. It's easy to overdo it with pills," she says.

Vitamin C

"Most people think it's fine to take as much as they want," says Rosenbloom. "I know people who take 10,000 mg a day." However, the upper tolerable limit is 2,000 mg a day. "People at risk for kidney stones can increase that risk; people also can get diarrhea. Some people have complained of food poisoning, but it turned out they had taken too much vitamin C. People just aren't aware how potent these vitamin supplements are."

Vitamin D

"This can be tricky because we need some, and as we get older we need more," Rosenbloom tells WebMD. "But the risk is that we get too much, which can actually cause calcium to leach out of your bones." Vitamin D is found in some calcium supplements; some orange juice products are fortified with vitamin D. If you're somebody who can't drink dairy, getting vitamin-fortified orange juice makes sense. "But if you do drink dairy, and then you take a supplement, it's that layering that I get concerned about," she says.

Vitamin B-6

This is a water-soluble vitamin, which means you just pee out the excess, says Rosenbloom. The upper tolerable limit is 100 mg day, and in pill form it's easy to get that much. "In high doses, people have problems with temporary nerve damage -- they lose feeling in their hands and feet," she tells WebMD.

Fifteen years ago, women were told to take megadoses to help with depression and PMS, but that's been debunked, she says.

Vitamin E

People focus on E to prevent Alzheimer's, heart disease, macular degeneration, cancer, "the list goes on," says Blumberg. The upper tolerable level is 1,000 milligrams (1,500 IU); the RDA is 30 IU. "There is no way to get an overdose from diet or fortified foods. In an Alzheimer's study, people took 2,000 IU for four years and didn't have any adverse effects. In another study, people took 800 IU for six years, with no adverse effects, he says.