Vitamins and Supplements: Do They Work?

Vitamins and dietary supplements are big--more than 110 million Americans forked over a collective $28 billion in 2010 on little bottles of would-be health magic. Research is unclear, however, on whether shoring up your diet with extra vitamins, minerals, and other supplements helps or hurts--in the short run or in reaching for the century mark.

For more than a decade, for example, researchers followed more than 35,000 men enrolled in SELECT, a clinical trial designed to see whether taking selenium and vitamin E might help prevent prostate cancer. In 2008, study participants received phone calls and letters: Stop the pills. Not only was the answer "no," but vitamin E apparently increased the chance of prostate cancer, if very slightly, and selenium seemed to do the same to diabetes risk. Later the same year, researchers from the Physicians' Health Study-II reported that neither vitamin E nor vitamin C reduced the chances of major cardiovascular problems or cancer as hoped.

That so many people seem to believe they need to boost their intake of vitamins and supplements is a triumph of marketing. Most Americans are well-nourished (besides being amply fed). Because much of our food is fortified with nutrients, once-common deficiency diseases such as scurvy and rickets, caused by inadequate vitamin C and D, respectively, have nearly disappeared in this and other developed countries. Researchers generally believe that with a few exceptions, like pregnant women or the elderly, most people don't need supplements. Over the 22-year course of the Iowa Women's Health Study, supplemental vitamin B6, folic acid, iron, magnesium, and zinc were associated with a slightly higher risk of premature death, copper to an 18 percent increased risk. Findings were published last year in the Archives of Internal Medicine. The study authors highlighted concerns about the long-term use of supplements and vitamins among those who do not have severe nutritional deficiencies. The pills, they concluded, are best used when recommended by doctors--not for general prevention.

A 2009 editorial in the Journal of the National Cancer Institute, meanwhile, warned that most vitamin studies show no cancer benefits, and that some found unexpected harm. Two studies of supplemental beta carotene, for example, found higher lung cancer rates, and folic acid research suggested a higher risk of colon polyps among those taking supplements than among those in a placebo group.

Still, some researchers maintain that the diets of many Americans fall somewhat short on certain key nutrients--not enough to threaten a return of those debilitating deficiency diseases, but perhaps enough to call for a little extra help. What follows is the current thinking--pro and con--on popular key supplements that have been well-studied.

Multivitamins. The U.S. Preventive Services Task Force neither recommends nor advises against multivitamins (or other supplements) for preventing cancer or cardiovascular disease. Yet many researchers say a multivitamin has a role as "a very inexpensive insurance policy," says David Schardt, senior nutritionist at the Center for Science in the Public Interest, a nutrition advocacy group in Washington, D.C. There's no need for anything fancy that claims "heart health" or "prostate health" benefits, he says; an inexpensive, basic brand is fine. In 2008, Harvard Men's Health Watch newsletter editor Harvey Simon recommended against multivitamins. His chief worry was that on top of already fortified foods, the folate in a multi could spur cancer. But a study since then showed that cancer was not increased in women at risk for heart problems who were given folic acid supplements. Simon is now less concerned about breast cancer risk, but prostate cancer still worries him.

[See: Popular but Dangerous: 3 Vitamins That Can Hurt You]

Calcium and vitamin D. Thumbs up. Extra calcium to protect bone health is safe and routinely prescribed for adults who get too little from food. In one study, men who consumed the most calcium (about 2,000 mg. a day) were 25 percent less likely to die over the next decade than their peers who got the least, according to findings published in 2010 in the American Journal of Epidemiology. The Iowa Women's Health Study also found that calcium supplements were associated with reduced risk of death over nearly two decades.

And consensus is building that Americans need more vitamin D to promote calcium uptake. It is produced by sun-exposed skin and is difficult to get from unfortified foods--fatty fish is the only major food source. Studies suggest vitamin D also may help fend off cancer and ward off infections. Still, no large-scale randomized controlled clinical trials prove vitamin D supplements offer benefits beyond bone health. Researchers are hungry for more evidence.

In 2010, the Institute of Medicine released new recommendations for daily calcium and vitamin D intake. Between 600 and 4,000 international units of vitamin D are advised, depending on age and gender, and between 700 and 2,500 milligrams of calcium.

[See: 4 Herbal Supplements Your Doctor Hates]

Fish oil. New findings are at odds with past evidence for the worth of the omega-3 fatty acids in fish oil, especially for heart-related conditions. An April analysis published in the Archives of Internal Medicine found that fish oil may not do much to ward off heart attacks and strokes in people who already have heart disease. Those taking fatty acid pills had about the same rates of heart disease, death from heart attacks, congestive heart failure, and stroke as those on placebo pills. But the findings don't necessarily mean that fish oil supplements are useless in heart patients. The study participants were all taking statins, powerful cholesterol-lowering medications, which could have trumped any benefits from fish oil.

The American Heart Association continues to recommend fish oil supplements for those at high risk of a heart attack. Simon, no fan of nutrients in pill form, says that, for those with heart risks who don't eat fatty fish like tuna and salmon twice a week, taking 1,000 mg or so is a good idea.

[See: Greek Yogurt Vs. Regular Yogurt: Which Is More Healthful?]

Antioxidants. The glowing promise of antioxidants remains elusive. These substances, among them selenium and vitamins A, C, and E, are believed to help sop up molecules called free radicals. These react with other molecules in the body and promote oxidative damage--another name for cellular wear and tear. "There's a lot of data supporting the idea that oxidation, over time, has a role in chronic illnesses," says J. Michael Gaziano, a chronic disease epidemiologist with Brigham and Women's Hospital and coauthor of the Physicians' Health Study-II papers.

Many observational studies suggest that people who gobble antioxidant-laden fruits and veggies or supplements have a reduced risk of some forms of heart disease and cancer. Most clinical trials, however, do not support this. Some research, in fact, has shown that supplemental vitamin E may actually increase the risk of lung cancer among smokers, as has been found with beta carotene, as noted above. Vitamin E may do the same. And cancer patients shouldn't add more vitamin C than the amount in a multi; research suggests that too much of the vitamin helps cancer cells withstand treatment.

Researchers are still studying whether supplemental antioxidants might slow the progression of age-related macular degeneration and perhaps prevent noise-related hearing loss. But "no doctor would recommend them for the prevention of cancer, of cardiovascular disease, or of dementia," says Simon.

What about you? Nutritional profiles are not all the same. Recommended intake varies by age, gender, and even race. And genetic differences mean everyone utilizes or responds to vitamins differently, says K. Simon Yeung, a research pharmacist in the Integrative Medicine Service at Memorial Sloan-Kettering Cancer Center. Diet preferences, such as a low-fat or vegetarian regimen, will alter the mix of nutrients taken in. Moreover, lab tests that analyze the nutrients in your system and indicate which ones might need boosting or trimming are, with a few exceptions, not readily available and not often performed. However, keeping tabs on your dining habits for a few days with SuperTracker, a U.S. Department of Agriculture tool, will give you a sense of whether you're on the right course. (It helps you plan, analyze, and track your diet and physical activity.)

Alice Lichtenstein, a professor of nutrition science and policy at Tufts University's Friedman School of Nutrition, worries that supplements give Americans license to continue their unhealthful ways so long as they pop a pill after the steak and hot fudge sundae. A balanced diet is still the best source of nutrients. Adding supplements--or fruits and veggies, for that matter--to a high-calorie diet is not going to work magic. Good health begins with physical activity and a balanced diet that is heavy on fruits, veggies, whole grains, "good" fats, and fish and light on red meat, "bad" fats, and processed food--and not too high in calories. "Nature," says Lichtenfeld, "is probably better than our manufacturers."

Updated on 5/9/2012: This story was originally published on Dec. 9, 2008. It has been updated.