Vitamins and supplements

New evidence shows they can't compete with Mother Nature

Consumer Reports on Health: March 2010

A healthful diet

Americans want to believe in vitamin and mineral pills: We spent an estimated $10 billion on them in 2008, according to the Nutrition Business Journal. But recent studies undertaken to assess their benefits have delivered a flurry of disappointing results. The supplements failed to prevent Alzheimer's disease, cancer, heart attacks, strokes, type 2 diabetes, and premature death.

"We have yet to see well-conducted research that categorically supports the use of vitamin and mineral supplements," says Linda Van Horn, Ph.D., a professor of preventive medicine at Northwestern University's Feinberg School of Medicine in Chicago. "Most studies show no benefit, or actual harm."

The power of food

While some people may need supplements at certain stages of their lives, nutritional deficiencies are uncommon in the U.S. "Almost all of us get or can get the vitamins and minerals we need from our diet," says Paul M. Coates, Ph.D., director of the Office of Dietary Supplements at the National Institutes of Health (NIH).

Major health organizations for cancer, diabetes, and heart disease all advise against supplements in favor of a healthful diet rich in fruits, vegetables, whole grains, and legumes. Unlike pills, those foods contain fiber plus thousands of health-protective substances that seem to work together more powerfully than any single ingredient can work alone. "That's why it's dangerous to say, 'I know I don't eat well, but if I pop my vitamins, I'm covered,' " says Karen Collins, R.D., nutrition adviser to the American Institute for Cancer Research. "We now know that you're not covered."

Too much can harm

Another concern is that some vitamin pills can be toxic if taken in high doses for a long time. Studies show that beta-carotene pills, for example, can increase the risk of lung cancer in smokers, and a 2008 review suggests that the pills, plus supplemental doses of the vitamins A and E, may increase the risk of premature death. In addition, a government survey found that more than 11 percent of adults take at least 400 international units of vitamin E a day, a dose that has been linked to heart failure, strokes, and an increased risk of death.

People are also apt to combine vitamin tablets and fortified foods, which can cause problems. For instance, too much folic acid—added to wheat products in this country—can mask vitamin B12 deficiency. Untreated, that can lead to irreversible nerve damage. In addition, high doses of folic acid may be associated with an increased risk of precancerous colon polyps, according to a trial of some 1,000 people at risk for them. "We're getting several alarming signals that more may not be better," says Susan T. Mayne, Ph.D., a professor of epidemiology at the Yale School of Public Health.

Yet despite the unfavorable results, vitamin and mineral pills are widely used to fend off diseases. Read on to find our review of the latest evidence on their effects.

Supplements strike out

Pill problems

There is insufficient evidence to support the use of supplements to prevent the following conditions:

Cancer. Two large trials published in 2009 came up empty. In one, sponsored by the National Cancer Institute, researchers reported that vitamin E and the mineral selenium failed to prevent prostate cancer. In fact, researchers noted possible increased risks of prostate cancer from vitamin E, and of type 2 diabetes from selenium. The second study, the Physicians' Health Study II, found that neither vitamin C nor E reduced the risk of colon, lung, prostate, or other cancers in men. And women haven't fared much better: Folic acid and certain other B vitamins provided no protection against breast or any other cancer in one study, and calcium and vitamin D had no effect on breast-cancer risk in another.

Some research suggests that vitamin and mineral supplements may pose particular risks to people who are being treated for cancer. While many cancer patients take antioxidant supplements such as vitamins C, E, and beta-carotene with the hope of reducing the toxicity of chemotherapy and radiation, a 2008 review found that the practice may protect cancer cells as well as normal ones. As a result, many oncologists now advise patients not to use antioxidant pills during those treatments.

Heart disease. Folic acid and other B vitamins failed to prevent heart attacks, strokes, and death from cardiovascular disease in women at risk for heart disease in a 2008 trial by the Harvard Medical School. And neither vitamin C nor E prevented those events in men in the Physicians' Health Study II. Vitamin E, however, was linked to an increased risk of hemorrhagic stroke.

Antioxidant supplements were previously thought to prevent fatty buildups in arteries, but research now suggests that they may worsen cholesterol levels and blunt the effects of cholesterol-lowering drugs. A 2009 review found that diets rich in those vitamins protected people from heart disease but supplements of them did not, underscoring the power of a healthy diet.

Type 2 diabetes. In a 2009 trial, vitamin and mineral pills didn't reduce the risk of metabolic syndrome--a cluster of symptoms including abdominal obesity and high levels of LDL (bad) cholesterol and blood sugar--that can lead to type 2 diabetes. Additional 2009 studies found that vitamin pills didn't prevent type 2 diabetes and might undermine the ability of exercise to improve blood sugar levels. And while many people with diabetes take supplements of the mineral chromium to control blood sugar and lose weight, that benefit is unproven.

Cognitive decline. B vitamins didn't slow Alzheimer's disease, and vitamin E failed to prevent dementia in people with cognitive impairment, according to trials from the Alzheimer's Disease Cooperative Study, an NIH-funded consortium. Another study suggested that high doses of vitamin E slowed the progression of moderate dementia, but most specialists are wary because of the potential risks, says Paul Aisen, M.D., director of the consortium.

On the other hand, a deficiency of vitamin B12 or thyroid hormone can cause cognitive impairment, so if you're declining more than normal for your age, you should be tested for those conditions. "But speak to your physician," Aisen says. "You can't necessarily replenish low B12 stores on your own."

Immune function. The evidence on whether vitamin and mineral supplements can enhance immunity is contradictory, especially for people who eat adequately. And while supplements can boost immune response in older people with nutritional deficiencies, it's still not known if that results in fewer infections. "In the vast majority of people, taking megadoses is not recommended, and may be harmful," says Kevin High, M.D., chief of infectious diseases at Wake Forest University School of Medicine in Winston-Salem, N.C. An excess of vitamin E, for instance, can backfire.

When a supplement might make sense

Vitamin and mineral pills can benefit certain people at different times in their lives, and some of those instances are listed below. But discuss the need for supplements with your physician first. They may be risky for some people and interfere with medications, or you may need a higher dose and different form. When possible, look for products labeled "USP-verified," which meets standards for quality, purity, and potency.

Supplement Recommended groups Daily amount Form
Vitamin B12 People over age 50; strict vegetarians At least 2.4 mcg from diet, supplements, or fortified foods Pills and dissolvable lozenges appear to be equally effective
Calcium People age 50 and older; strict vegetarians 1,000 mg for adults under age 50, and 1,200 mg for people age 50 and older from food and supplements Whatever is cheapest and most palatable; absorption appears highest in doses under 500 mg at a time
Vitamin D People age 50 and older; adults with limited sun exposure 800 to 1,000 IU from fortified foods and supplements Vitamin D3 may be more potent than vitamin D2
Eye supplement People with at least moderate macular degeneration in one or both eyes A formula containing 500 mg of vitamin C, 15 mg of beta-carotene, 400 IU of vitamin E, 80 mg of zinc oxide, and 2 mg of copper Name-brand or generic versions are acceptable; dollar store and deep discount brands may be substandard
Iron Premenopausal women with heavy periods 8 mg for ages 9 to 13; 15 mg for ages 14 to 18; 18 mg for ages 19 to 50 Ferrous iron is best absorbed

For eye disease, bone loss

Some evidence supports the use of supplements for these conditions:

Eye disease. People who have at least moderate age-related macular degeneration (AMD), a leading cause of blindness, may be able to limit further damage by taking a daily supplement that contains vitamins C, E, and beta-carotene. But talk with your ophthalmologist first, since the formula could be risky for some people.

Recent research suggests that folic acid and other B vitamins reduce the risk of developing AMD for some people. "This is the first suggestion of a way of preventing the early stages of AMD other than avoiding smoking," says William G. Christen, Sc.D., an associate professor at Brigham and Women's Hospital in Boston. But the study, sponsored by the National Eye Institute, needs to be repeated before firm recommendations can be made.

Osteoporosis. In a recent comprehensive review of 167 studies, the federal Agency for Healthcare Research and Quality found that calcium and vitamin D pills reduced fractures and bone loss--although the fracture benefit was primarily only in female nursing-home residents. Vitamin D alone also helped prevent falls in older people in a 2009 analysis, but only at doses of 700 IU a day or higher.

Shortfalls of vitamin D are common, recent research suggests, so if you have health problems possibly linked to abnormal calcium metabolism or vitamin D deficiency such as hyperthyroidism and osteoporosis, consider having your blood levels tested. If your reading is low, your doctor will probably prescribe a high-dose vitamin D supplement for a few months, and then retest.

When a supplement might make sense

Vitamin and mineral pills can benefit certain people at different times in their lives. But discuss the need for supplements with your physician first. They may be risky for some people and interfere with medications, or you may need a higher dose and different form. When possible, look for products labeled "USP-verified," which meets standards for quality, purity, and potency.

Who really needs a multi?

The evidence that multivitamins offer little if any protection for the average person keeps growing. For example, researchers from the Women's Health Initiative studied more than 161,000 women, comparing those who took the pills with those who didn't. After eight years, they detected no benefit. Still, there are some groups of people who may benefit from them.

Dieters. Most people who need to lose weight can cut calories and still get all the nutrients they need from food. But if a health-care professional advises cutting calories severely, you should consider taking a multivitamin.

Strict vegetarians. Unless they eat fortified foods, vegetarians who exclude eggs and dairy products can have inadequate amounts of calcium, vitamin B12, iron, and zinc. They could consider a multivitamin, though they may be better off with single supplements, since multis may not have enough of the nutrients they need and too much of those they don't.

People with certain disorders. Those include conditions that impair the ability to digest or absorb nutrients, or illnesses that deplete them. If you have a medical reason for taking a supplement, you should get advice from your doctor about what to take and how much. You may need more absorbable forms and higher doses than multivitamins provide.

People with poor diets, especially the very old. People who don't eat enough to maintain their weight might need more than a standard multivitamin. They should consult a doctor or dietitian.

Women who are pregnant, tryin to become pregnant, or breastfeeding. Many pregnant women consume less than the 400 micrograms of folic acid a day that helps prevent neural-tube defects in newborns. Pregnant and breast-feeding women also need more of other nutrients, notably calcium and iron. They should take a specially formulated prenatal multivitamin.

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