Vitamin supplements are widely used in the United States, especially among adults ages 65 and older—but there's scant evidence that they work to prevent chronic diseases, Liz Szabo writes for Kaiser Health News reports.
Who's taking supplements?
According to Szabo, there are more than 90,000 dietary supplements for sale in the United States, and millions of Americans purchase them.
A 2013 Gallup poll found half of U.S. adults regularly take vitamins or other mineral supplements. The percentage is highest among older populations. For instance, the poll found 58% of Americans ages 50 to 64, and 68% of Americans ages 65 and older, take vitamins or other mineral supplements. In comparison, 36% of Americans ages 18 to 29 to such supplements.
People who use mineral supplements often do so for life, Szabo writes, despite long-term studies that show vitamins rarely prevent disease, and in some cases result in harm.
Inside the research
NIH has spent more than $2.4 billion on research evaluating the effectiveness of vitamin and mineral supplements since 1999, Szabo writes. Barnett Kramer, director of cancer prevention at the National Cancer Institute, said despite the investment, there isn't "much to show for it."
According to Szabo, it's not uncommon for preliminary research to show vitamin supplements yield health benefits, but more rigorous studies rarely find any benefits. In fact, some research on vitamin supplements has shown a link between high doses of vitamin supplements and death and heart failure.
For instance, while early studies indicated beta carotene—which is found in carrots—might reduce cancer risk, two large, well-designed clinical studies in the 1990s showed beta carotene pills were tied to higher lung cancer rates—a finding that Szabo writes shocked experts.
The research takeaway
JoAnn Manson, chief of preventive medicine at Brigham and Women's Hospital, said to date there's no strong evidence that dietary supplements can help ward off chronic conditions in the average American
Kramer said the apparent lack of effectiveness of vitamin supplements stems in part from the fact that most Americans get the needed amounts of vitamins and minerals in their daily diets. According to Szabo, food sold in the United States is well fortified: milk typically contains vitamin D, salt can contain iodine, and flour has vitamin B.
Marjorie McCullough, strategic director of nutritional epidemiology for the American Cancer Society, said part of the reason why vitamin supplements might not be as effective as vitamin-rich foods, such as fruits and vegetables, is that scientists have yet to fully understand how different foods work together, and therefore have not been able to successfully replicate those interactions in pill form.
However, Walter Willett, a professor at the Harvard T.H. Chan School of Public Health, said it is reasonable for individuals to take a daily multivitamin "for insurance." He said research has underestimated the true health benefits of vitamin supplements, because the studies have not been long enough to see whether vitamin supplements have an effect on cancer or heart disease.
Catherine Price, the author of "Vitamania: How Vitamins Revolutionized the Way We Think About Food," also said research on vitamins may underestimate their effects because it can be difficult to find a control group that has not been exposed to vitamins through fortified foods. As a result, vitamin supplements might appear less effective if everyone in a study is exposed to such foods.
But for those who do take vitamins and other mineral supplements, Eric Klein of Cleveland Clinic cautioned against overuse. He said vitamins "are biologically active agents," which means "[w]e have to think of them in the same way as drugs. If you take too high a dose of them, they cause side effects" (Szabo, Kaiser Health News, 4/4).
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