点击显示 收起
A morning multivitamin. A couple of E's. Maybe some C. A protein shake for lunch. A calcium pill or two, later in the day. We've come a long way since our Flintstones days. But are Americans overdoing it?
It's true, vitamin-fortified foods are flying off store shelves. Even orange juice comes with calcium and vitamin D. Energy bars, meal-replacement drinks, protein shakes, cereal bars, cereal itself -- all claim lots of vitamins and minerals, up to 100% of the recommended daily allowance (RDA).
Then, too, specially blended multivitamins -- with hot new "additives" such as green tea -- are nearly irresistible to health nuts.
But you do the math: You could be getting up to 500% of the RDA, maybe more, in one day's time -- up to five times what your body needs. Are we toting up toxic levels of vitamins? Or throwing our money away?
Experts Weigh In
Chris Rosenbloom, PhD, RD, professor of nutrition at Georgia State University in Atlanta, counsels plenty of people who are overdoing it.
"If you're eating two energy bars a day, plus a protein shake that is vitamin fortified, plus taking vitamin supplements, you don't need all that," says Rosenbloom.
But most people still aren't getting the right vitamins despite their best efforts, says Jeffrey Blumberg, PhD, professor of nutrition at Tufts University in Boston. "Most people need a multivitamin as 'insurance.' Everybody needs to eat more healthfully. While you're trying to get there, take supplements."
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.
Read the Label
Pay attention to food labels, says Rosenbloom. "When you're grocery shopping, picking up an energy bar or breakfast cereal, look at the supplement facts panel. If you see 100% of RDA, you may not need a multivitamin supplement."
For a small fee, a nutritionist can evaluate your diet for deficiencies. Also, some online programs provide the same service.
"People are often very surprised when they see the nutrients they are getting and what they're not," says Rosenbloom. "Maybe they need a calcium supplement, maybe your vitamin C is low if you don't eat any citrus."
Won't Prevent the Inevitable
Blumberg's prudent advice: "Take a multivitamin. Take a calcium supplement, if you don't drink much milk. If you're taking medicine that interferes with nutrient absorption, if you're an older person whose calorie intake is low, if you're an athlete, if you're pregnant -- all of those are good reasons to take a multivitamin supplement."
Just stay away from those whopper-sized, 25,000 milligrams, vitamin A pills, he says.
"By and large, nutrient supplements -- vitamins, minerals -- are enormously safe," Blumberg says. "Even if you drink a gallon of OJ a day, eat fruits and vegetables, then take 1,000 milligrams of vitamin C, you're not going to even get close to toxicity."
Originally published June 19, 2003.
Medically updated August 2005.
SOURCES: Jeffrey Blumberg, PhD, professor of nutrition, Tufts University, Boston. Chris Rosenbloom, PhD, RD, professor of nutrition, Georgia State University, Atlanta. National Institutes of Health web site.