At least half of American adults take vitamins and other supplements regularly, spending more than $23 billion a year on these nutritional aids in the belief that supplements can help prevent disease and improve health. However, evidence suggests that many supplements may be ineffective—and, in large doses, some may even do more harm than good.

Here's what you need to know now…


According to a recent report by a panel of advisers at the National Institutes of Health, there is not enough evidence to recommend the use of multivitamin and mineral supplements to prevent chronic disease. And most people taking multivitamins don't really need them.

Reason: These individuals tend to be health conscious anyway, getting important nutrients from the food they eat.

There are, however, some people who do need supplements…

  • Anyone who eats fewer than 1,500 calories per day should take a daily multivitamin that contains 100% of the Recommended Dietary Allowance (RDA) of all key nutrients.
  • Women who are trying to conceive and those who are in the first trimester of pregnancy should take a daily prenatal multivitamin—which has 400 micrograms (mcg) of folic acid. Folic acid has been shown to reduce the risk of birth defects.
  • People over age 50 should take a B-12 supplement or a multivitamin containing at least the RDA of 2.4 mcg of B-12 if they don't get that amount in fortified foods, such as cereals. That's because as people age, the stomach produces less acid to digest food, making it difficult to absorb B-12 from food.
  • Those over age 70 have trouble getting enough calcium and vitamin D from food.

Example: To get the recommended amount of calcium, they would have to drink a quart of milk a day. People in this age group should have at least 600 international units (US) of vitamin D (15 mcg) and 1,200 milligrams (mg) of calcium a day.


The real concern is with the millions of Americans who consume nutrient-specific supplements in dosages that far exceed the RDAS.

Examples: Many people take vitamin C pills in hopes of boosting immunity and preventing colds...vitamins B and E to protect their hearts...beta-carotene and other antioxidants to help fight cancer.

Below are common supplements and the possible health problems that may result from taking high doses…

  • Vitamin E. Although this antioxidant has been touted to improve heart health, recent "gold-standard" studies-randomized trials in which participants who are not aware of whether or not they are taking a supplement or a placebo are carefully tracked-show the opposite may be true. One meta-analysis, led by researchers from the Johns Hopkins School of Medicine, analyzed 19 previous trials involving almost 136,000 people and found that vitamin E supplements-especially in the often-sold daily dosage of 400 IUS-caused a slight increase in death from heart attack. In another study of 9,500 people, those who took vitamin E had a 13% higher risk of heart failure

Another danger: Vitamin E supplements could interfere with chemotherapy or radiotherapy by suppressing free-radical production, which is necessary to kill cancer cells.

  • B vitamins. Until recently, the belief was that vitamins B-6, B-12 and folic acid reduced the risk of heart attack and stroke by lowering the level of homocysteine in the blood, a well-documented risk factor for coronary artery disease. However, one recent study published in The New England Journal of Medicine, which followed people who had had a heart attack, found that the risk of a second attack increased after taking B-vitamin supplements.

Another danger: In animal studies, high doses of B vitamins seemed to stimulate cancer growth. There is no proof of this effect in humans, but there is a theoretical risk.

  • Vitamin C. Contrary to popular wisdom, there's no credible evidence that vitamin C supplements help prevent colds, although they may shorten the duration by a day or so. For people who eat healthfully, supplementing with vitamin C does not seem to boost immunity,

Dangers: Vitamin C supplements raise the risk of kidney stones. As with vitamin E, Vitamin C supplements should be avoided by cancer patients who are undergoing chemotherapy or radiotherapy.

  • Vitamin A and beta-carotene. Vitamin A comes in two forms--as preformed vitamin A or as one of several carotenoids, of which beta-carotene is the best-known. Both forms of vitamin A supplements have proved risky.

Beta-carotene supplements have been found to speed the risk of death from lung cancer and heart disease in people who smoke. More recently, a study of 75,000 people found that supplements of preformed vitamin A as well as diets rich in vitamin A-increased the risk of hip fractures by 48%. This was observed with dosages just slightly above the RDAs of 900 meg for men and 700 mcg for women.

Other dangers: Unless you are deficient in vitamin A—rare in the US—taking supplements containing more than 3,000 mcg (10,000 IUS) can cause liver damage. In pregnant women, high-dose vitamin A supplements may cause birth defects.

  • Glucosamine and chondroitin sulfate. In a recent federally sponsored clinical trial, the often-used combination of glucosamine and chondroitin sulfate, once believed to reduce osteoarthritis knee pain by rebuilding cartilage, proved no more effective than a placebo for most of the 1,583 participants. Only a small group of patients with severe arthritis experienced slight relief.

Dangers: Mild gastrointestinal upset is a possible side effect. Theoretically, people with seafood allergies may be allergic to glucosamine, which is derived from shellfish.

Saw palmetto. Although taken by millions of men with an enlarged prostate, the herb saw palmetto didn't relieve symptoms any better than a placebo in a recent well-respected randomized trial published in The New England Journal of Medicine.

Dangers: Saw Palmetto should not be taken with blood thinners, such as aspirin or warfarin (Coumadin). Possible side effects of saw palmetto include stomach pain, nausea, diarrhea and impotence.

  • Zinc. Another antioxidant nutrient, zinc was once believed to help boost immunity and prevent colds. However, in most studies, supplements seem to benefit only those with zinc deficiency, which is rare among Americans eating a balanced diet.

Danger: Zinc supplements lower the body's copper levels, which in turn may increase the risk of cardiac arrhythmia.

  • Copper. In adequate amounts—the RDA of 09 mg—copper helps in the formation of red blood cells, nerve fibers and collagen for healthy skin and bones. It also acts as an antioxidant. However, in higher amounts, copper may work as a pro-oxidant, promoting free-radical damage that could contribute to Alzheimer's disease-especially in people who eat a high-fat diet.

In a six-year study of 3,718 people whose average age was 75, recently published in Archives of Neurology, the rate of memory loss and other cognitive decline was equivalent to 19 years of aging in those who consumed 2.75 mg of copper per day-levels found in some multivitamins and ate a diet rich in saturated and trans fats. However, copper intake wasn't associated with mental decline in people who ate low-fat diets.

Another danger: The risk of liver damage occurs with dosages above 10 mg a day.

The Bottom Line

Although high levels of certain nutrients help prevent disease and improve health, the benefit typically comes from diets rich in those vitamins and minerals. Foods also contain health-protecting phytochemicals—some of which have not yet been identified—and these substances are not in supplements.

The old advice still is best—eat a healthful, well-balanced diet to meet the RDAs of necessary nutrients.

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