Vitamins: Separating Fact From Fiction (cont.)
Calcium supplements are also important for certain age groups, Bailey says. The Institute of Medicine, part of the National Academy of Sciences, recommends that adolescents get 1,300 milligrams of calcium a day. One cup of milk or calcium-fortified orange juice contains about 300 milligrams of calcium.
Other sources of calcium include cheese, tofu, yogurt, vegetables, and beans. A typical calcium supplement may contain 500 milligrams or 600 milligrams of calcium. Bailey gives her 15-year-old son a daily calcium supplement at dinnertime. People over 50 should get 1,200 milligrams a day of calcium to ward off osteoporosis (thinning of the bones), Bailey says.
Federal dietary guidelines recommend that the elderly, the homebound, and people with dark skin boost their vitamin D intake with both fortified foods and supplements to reduce the risk of bone loss. Vitamin D helps with absorption of calcium; often calcium supplements will also contain vitamin D. (The full federal guidelines, updated in 2005, are available at www.health.gov/dietaryguidelines.)
Special groups such as smokers, pregnant women, or people recovering from traumatic injury may need additional supplements, Cross says. Decisions to take supplements beyond a multivitamin are best made with your doctor or registered dietitian, she says.
The evidence is strong that a healthy diet can ward off chronic diseases like cancer and heart disease. What's less clear is if big intakes of particular micronutrients can boost that preventive effect further.
There is promising evidence that the mineral selenium could prevent a variety of cancers, says Alan Kristal, DrPh, associate chief of cancer prevention at the Fred Hutchinson Cancer Research Center in Seattle. But beyond selenium, the data aren't promising, Kristal says. For example, there's no solid evidence that taking large doses of antioxidants like vitamins B or C have any beneficial effect.
As you seek the proper multivitamin or dietary supplement, it's best to keep your guard up. The supplement industry is relatively unregulated, and you can injure or even kill yourself with "natural" products bought at your neighborhood supplement store.
Many health claims attached to multivitamin formulations are doubtful, but harmless. Some men's multivitamins contain extra lycopene, a substance once thought to prevent prostate cancer. But Kristal, the cancer specialist, says support for that claim is waning. "If indeed lycopene did anything, [supplements] don't have enough to make a difference," he says. Multivitamins aimed at women are often spiked with green tea or ginseng extract; the effect of these on weight control is yet unproven.
More dangerous are recommendations of vitamin megadoses to treat obesity, depression, carpal tunnel syndrome or other problems. At best, megadoses are a distraction from real treatments for these problems, experts say. At worst, they can cause injury or death.
So-called fat-soluble vitamins -- that is, vitamins A, D, E, and K -- accumulate in the body, making overdosing a real threat. Vitamin overdoses have been associated with liver problems, weakened bones, cancers, and premature mortality.
Until recently, water-soluble vitamins such as B and C were considered nontoxic, even at high doses. But now evidence is emerging that B-6 megadoses can cause serious nerve damage, Bailey tells WebMD.
Despite the warnings, the quest for a magic pill plunges ahead. Cross chuckles when patients show her weight loss supplements that claim wondrous effects "when taken in combination with a sensible diet and exercise." Her response: Wouldn't a sensible diet and exercise do the trick even without the supplement?
Published March 3, 2006.
SOURCES: Harvard School of Public Health web site: "Vitamins." Mayo Clinic web site: "Vitamin and mineral supplements: Use with care." U.S. Department of Health and Human Services: "Dietary Guidelines for Americans 2005." Lynn B. Bailey, professor of human nutrition, food science and human nutrition, University of Florida, Gainesville. Audrey Cross, PhD, associate clinical professor of nutrition, Mailman School of Public Health, Columbia University. David Grotto, registered dietitian; spokesman, American Dietetic Association. Alan Kristal, DrPh, professor of epidemiology, University of Washington; associate director of cancer prevention, Fred Hutchinson Cancer Research Center.
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Last Editorial Review: 3/3/2006