When the Institute of Medicine announced last fall that it was changing the amount of vitamin D it recommends most adults get each day from 200 international units (IU) to 600 IU, some critics said the increase was too modest. They cited studies associating higher vitamin D levels with several disease-preventing benefits, in addition to its well-documented role in protecting bones.
But sometimes a conservative approach is justified. For example, it wasn't that long ago that researchers thought folic-acid supplements might protect the heart or prevent cancer, a promise that clinical trials have failed to confirm. Studies of antioxidant supplements have been equally disappointing. In an analysis of 67 trials involving about 230,000 patients, for example, the pills had no beneficial effect on mortality. And three antioxidant vitamins—A, E, and beta-carotene—actually increased the risk of death.
Even the good old multivitamin, far and away the supplement purchased most often in the U.S., has virtually no evidence to show that it improves the average person's health.
Supplements have their place, but "many of the claims are overblown and unsubstantiated," says JoAnn Manson, M.D., chief of preventive medicine at Brigham and Women's Hospital in Boston and a member of the institute's committee on vitamin D. "People are often given the impression that supplements work better than they really do."
Still, more than half of American adults have taken them. So we looked at the evidence for the top five vitamin supplements (excluding multivitamins), based on 2009 sales data from the Nutrition Business Journal, a trade publication. Below is our take on the potential risks and benefits of each, plus advice about who should consider taking them.
Note that the Food and Drug Administration doesn't require supplements to go through the same rigorous testing for safety and efficacy that drugs do.
And certain ingredients can cause serious side effects. If you take supplements, look for products with the "USP Verified" mark, which means they meet standards of quality, purity, and potency set by the nonprofit U.S. Pharmacopeia.
Some marketers of supplements would like you to think that B vitamins provide a power boost. The vitamin supplements do help you extract energy from food, but most people get plenty through their diet. Extra doses won't necessarily make you more energetic.
Nor do the vitamins appear to reduce heart risk. In an October 2010 analysis of trials involving more than 37,000 people at high risk of cardiovascular disease, those who took folic acid, a B vitamin, did have lower levels of homocysteine—a chemical linked to an increased risk of heart disease—compared with those who took a placebo. But they didn't have significantly fewer heart attacks or strokes. Nor did the pills reduce the risk of cancer or premature death.
Preliminary research does suggest that a combination of B6, B12, and folic acid might reduce the risk of age-related macular degeneration, a progressive eye disease that causes vision loss. But larger trials are needed to confirm that.
Bottom line. Most people don't need B vitamin supplements, but they might make sense for a few groups:
People whose diets include lots of vitamin C—rich fruit and vegetables appear to have a lower risk of heart disease and certain cancers, among other diseases. But clinical trials testing isolated doses of the vitamin in pill form have mostly failed to find any protective benefit against those diseases.
That could be because vitamin supplements don't provide the fiber or the myriad beneficial phytochemicals that a colorful mix of produce does. Some data (though sometimes from questionably designed studies) has even suggested that supplements of antioxidant vitamins, including C, might pose risks for people being treated for cancer by protecting tumor cells along with normal ones.
There's some evidence that 200 mg or more of vitamin C a day might improve cold symptoms in smokers and seniors, though it won't prevent colds. And there's some preliminary evidence that a supplement combining large doses of vitamins C and E, beta-carotene, copper, and zinc might slow the progression of macular degeneration.
Bottom line. In general, just 90 mg of vitamin C a day for men and 75 mg for women is sufficient. Smokers should add an extra 35 mg a day—the amount in about half an orange—to help repair damage from cancer-causing free radicals. Vitamin C can enhance iron absorption, so avoid high doses if you have hemochromatosis, a condition in which the body absorbs and stores too much iron. Talk with your doctor before taking any antioxidant supplement if you are undergoing cancer treatment.
Not everyone's latitude or lifestyle permits adequate sun exposure to make ample amounts of vitamin D, which the skin synthesizes from sunlight. That's especially true during winter months—one reason the Institute of Medicine, which advises the government on nutrition recommendations, decided on an increase in the suggested daily intake.
While that might help improve vitamin D intake in certain populations, "the epidemic of vitamin D deficiency in North America is largely a myth," Manson says. Indeed, population studies have found that low blood levels of the vitamin are less common than previously thought. And while some large, observational studies have linked higher vitamin D intake to a lower risk of cancer, heart disease, and other conditions, they can't prove cause and effect; only large, randomized clinical trials can do that. And people with low levels of vitamin D might have other risk factors, such as obesity, a sedentary lifestyle, or a poor diet, that could increase their likelihood of disease, Manson points out.
Bottom line. Until research confirms the benefit of higher doses, stick with the IOM's recommendation: 600 IU for adults up to age 70 and 800 IU for those older than 70. If you get some midday sun exposure during the warmer months and regularly consume vitamin D-rich foods, such as fatty fish, eggs, or fortified dairy products, you probably don't need vitamin supplements. People who are middle-aged or otherwise at risk of vitamin D deficiency, including those who are overweight or have darker skin,might need supplements. Even then, the amount in most multivitamins is probably enough. Don't exceed 4,000 IU a day. If you're unsure about your vitamin D status, request a blood test.
On paper, vitamin E appears to strengthen the immune system and reduce the risk of heart disease and cancer. Research has found that it can help protect cells from damage, widen blood vessels, and inhibit the formation of artery-clogging clots.
But like its antioxidant cousins, vitamin E supplements haven't been found to offer any conclusive protection against disease in large clinical trials, and they might even be risky. Two analyses have linked doses of E as low as 400 IU a day—and possibly even lower—to a small but statistically significant increase in mortality.
The synthetic form of the vitamin is less active than the natural form, which is found in nuts, seeds, and vegetable oils. (Supplements can contain either form.) Most single-ingredient vitamin E supplements contain much larger doses than recommended.
Bottom line. For most people, any theoretical benefits from supplemental E are far outweighed by the risks. The vitamin may inhibit blood clotting, so it shouldn't be taken with blood thinners.
Same song, different verse. Studies have linked diets rich in vitamin A and betacarotene, a precursor of the vitamin found in plant foods, to a lower risk of many types of cancer. But clinical trials of beta-carotene supplements have found that they offer no protective benefit against cancer. And large doses have actually been found to increase the risk of lung cancer in smokers.
Few people in the U.S. are outright deficient in vitamin A. The retinol form—which comes from animal sources like eggs, liver, and whole milk—is more readily absorbed than beta-carotene, but even strict vegetarians can usually meet their needs by eating the recommended five servings a day of produce, including both dark green leafy vegetables and orange and yellow fruit.
There's another reason to avoid high-dose supplements: Taking too much vitamin A as retinol can cause birth defects and liver abnormalities, and some evidence suggests it might also harm the bones. (The levels in most multivitamins today are probably fine.)
Bottom line. Not recommended.
If you eat a healthful diet, you probably don't need a multivitamin/multimineral supplement, commonly referred to as a"multivitamin." And large clinical trials have repeatedly found that the pills don't improve the average person's health. But you wouldn't know that from visiting the vitamin aisles, which are filled with not just basic multivitamins but also special formulations for men, women, teenagers, seniors, menopausal women, and dieters, among others.
Do you even need a multivitamin, and if so, should you bother getting one targeted to your specific demographic? Use this quick guide to decide.
Some people might not be able to meet their nutritional needs through diet alone. Those include women who are pregnant, breast-feeding, or trying to conceive; those consuming fewer than 1,200 calories a day or who are cutting out an entire food group (carbs, for example); and those who have a condition that depletes nutrients, such as cancer or diabetes.
In addition, people older than 50 might need help getting the recommended 600 international units of vitamin D (or 800 iU for those older than 70) and at least 2.4 micrograms of B12 daily, since the body's ability to absorb those from food declines with age. A multivitamin is one source for those nutrients, but so are individual supplements and fortified foods (such as a breakfast cereal with B12).
Formulas that contain iron can be a good choice for premenopausal women, who might need to compensate for iron loss from menstruation. Men and older people typically don't need more iron and should look for a formulation without it. Botanical ingredients and food extracts found in some specialty formulas are often present in such small amounts that they're essentially useless—and that's if they even had a proven benefit to begin with. And look out for unexpected additions: One a Day Women's Active Metabolism contains 120 milligrams of caffeine per pill—more than the amount in a can of Red Bull—plus guarana seed, a natural stimulant.
In addition, these tips can help you wade through the claims: