Antioxidants -- mainly vitamins C and E, selenium, and beta-carotene -- are the darlings of the nutritional-supplement world. But the nation's top scientists have studied the evidence, and they're saying the same thing nutritionists have said for years:
Most of us don't need antioxidant supplements, as long as we eat a healthy diet.
According to a report by the Institute of Medicine, a part of the National Academies of Sciences, researchers found no evidence that large doses of antioxidants prevent chronic diseases. Seems like a contradiction to what you've heard? Here are the facts.
While there is evidence that free radicals (compounds that cause damage to cells) are linked to a risk of cancer and heart disease, there is no proof (at least, not yet) that antioxidants in humans attack free radicals or limit their damage. It's only been proven in laboratories. Therefore, no evidence exists that taking megadoses of antioxidants prevents cancer, heart disease, or Alzheimer's disease. "The public is very confused because often when these studies get reported, all the facts aren't in," says Sandra Schlicker, director of the study at the Institute of Medicine.
The National Institutes of Health panel did revise the recommended Dietary Allowances (RDAs) -- the minumum amount needed for good health. And, for the first time, they set an upper-intake level -- the most a person can take without risking health problems. This doesn't mean larger amounts are harmful, just that not enough research exists to say for sure that bigger doses are safe. In revising the RDAs, the experts looked at published studies and focused on trials involving humans -- not animals.
The take-home message of this report is simple: Eat more fruits and vegetables every day. While the panel did not say how many to eat, it did endorse the five-a-day eating plan, which advises people to eat at least five servings of fruits and vegetables a day. A typical serving is one apple, orange, or pear, 1/2 cup of berries, cut-up fruit, or cooked vegetables. One 6-ounce glass of juice also is considered a serving.
Its claim to fame: Vitamin E has been associated with reducing heart disease because it blocks oxidation of LDL (bad) cholesterol, making the cholesterol less likely to cling to artery walls. However, only one out of four large-scale trials of megadoses of vitamin E showed a reduced risk of heart attacks.
Old RDA: Women, 8 milligrams (12 IU). Men, 10 milligrams (15 IU).
New RDA: 15 milligrams (22 IU) of natural vitamin E, also called d-alpha-tocopherol, for adults.
Recommended upper limit: 1,000 mg per day from supplemental sources, for adults 19 and older. (A lower limit is recommended for children.) Anything higher increases your risk of uncontrolled bleeding.
Best food sources: Vegetable oils, such as sunflower and safflower; nuts; and seeds. Smaller amounts of vitamin E are found in dairy foods, eggs, beef, whole grains, fruits, and vegetables.
Supplement notes: Because vitamin E is found in fat, some people may need to meet the RDA by taking a supplement. "If you're eating 3,000 calories a day, it's easy to get your 15 milligrams, so don't worry about it," says Maret Traber, Ph.D., associate professor at the Linus Pauling Institute at Oregon State University and Institute of Medicine panelist. "If you're eating only 1,500 calories a day, you may have trouble getting there. I'd rather see someone take a vitamin E supplement and eat a low-fat, low-calorie diet rich in fruit and vegetables than for the person to eat more fat just to get the vitamin E," Traber says.
When buying the supplement, look for natural vitamin E, also known as d-alpha-tocopherol. Researchers used to think synthetic vitamin E, known as dl-alpha-tocopherol, was just as effective, but it is not, Traber says. Many multivitamins contain synthetic vitamin E, Traber warns, so check labels carefully.
Its claim to fame: Many studies have found an association between vitamin C and a reduced risk for cancer and heart disease, although few established a true cause-and-effect relationship.
Robert A. Jacob, Ph.D., a member of the institute's panel and research chemist with the USDA Western Human Nutrition Research Center in Davis, California, says most of the studies on megadoses of vitamin C had mixed results or were neutral, including those that linked vitamin C to staving off the common cold or preventing heart disease and cancer.
"Studies didn't show harmful outcomes. But if they didn't show consistently positive results, you can't use that as a basis for an RDA," Jacob says.
Most of the research on vitamin C has never shown direct cause and effect. Studies have found only an "association" with health benefits. For example, research may show that people with a high vitamin C intake have lower blood pressure. However, there is no scientific proof that the vitamin is responsible because many other components of a healthy diet may lower blood pressure. "There is an association there, but it doesn't prove that vitamin C lowers blood pressure," Jacob says.
Old RDA: 60 milligrams for all adults.
New RDA: 75 mg per day for women, 90 mg per day for men. People who smoke should increase the RDA of vitamin C by 35 milligrams.
Recommended upper limit: 2,000 mg per day, for adults over age 19. The NIH report notes that the risks associated with exceeding this limit are very low, although exceeding the upper intake limit may cause gastrointestinal distress.
Best food sources: Citrus fruits and juices, kiwifruit, broccoli, strawberries, and red or green sweet peppers. It's easy to get enough vitamin C in your diet. One 6-ounce glass of orange juice, for example, has about 78 milligrams. Vitamin C-rich fruits and vegetables typically average about 40 milligrams per serving, Jacob says.
Its claim to fame: Studies have suggested a link between selenium intake and reduced risk of prostate, colon, and lung cancer. But so far none have been conclusive enough to warrant adding a supplement with this nutrient. In fact, if you live in the United States, chances are you're getting enough selenium in your diet. The reason: selenium is in the soil. Produce grown in selenium-rich soil will contain the mineral, says Dr. Raymond Burk, director of clinical nutrition research unit at Vanderbilt University.
Old RDA: 55 micrograms for women, 70 micrograms for men.
New RDA: 55 micrograms for all adults.
Recommended upper limit: 400 micrograms, for adults age 19 and up. This limit was set because too much selenium causes hair to fall out, and makes nails brittle.
Best food sources: Brazil nuts, seafood, meat, chicken, and whole-grain foods.
Their claim to fame: There appears to be a link between carotenoids (including beta-carotene, lutein, zeaxanthin, and lycopene) and a decreased risk of age-related macular degeneration, cataracts, and some cancers. However, no clinical trial has shown that carotenoids -- compounds found in red and yellow plants -- are responsible for lowering risk.
"There is encouraging research with certain carotenoids in the prevention of some diseases, but not enough to say what the requirement should be," says Susan Taylor Mayne, Ph.D., associate professor of epidemiology and public health at Yale University School of Medicine. There are some promising associations, such as with lutein and macular degeneration, but they are preliminary, she says.
So all the articles written about lycopene's effect on prostate cancer don't mean much? "It's all interesting data, but at this point, it is far from proven," Mayne says. "And most of the studies have been done on food, not pills." Mayne recommends getting your carotenoids by eating a variety of foods.
Old RDA: None. There never was one.
New RDA: None, although the NIH report recommends eating 5 fruits and vegetables a day to take in 3 to 6 mg.
Recommended upper limit: Beta-carotene supplements are not advised other than as a source of vitamin A. Beta-carotene and lycopene in excess of 30 mg per day -- whether from foods or in supplemental form -- can cause a harmless yellowing of the skin. (This goes away when the intake is reduced.) The NIH review of the research suggests that excessive intake from food sources is otherwise not harmful, though high doses of supplements may pose some risk.
Best food sources: Sweet potatoes, carrots, tomatoes, peppers, spinach, kale, collard greens, squash, apricots, mangoes, cantaloupe, and papayas.