Taking vitamins to prevent cancer or heart disease may backfire


If you are taking vitamin supplements to reduce your risk of heart disease or cancer, a government panel of health experts wants you to know that you’re probably wasting your money. In some cases, those vitamins may actually increase your risk of cancer.

The U.S. Preventive Services Task Force came to this conclusion Monday after reviewing dozens of studies, including many randomized clinical trials, considered the gold standard for medical research. The task force’s final recommendation was published online Monday in the Annals of Internal Medicine.

Nearly half of adults in the U.S. take at least one vitamin or mineral supplement on a regular basis, including the 32% of adults who take a multivitamin-multimineral. These pills are advertised as a way to promote general health. In some cases, manufacturers promote them as cancer fighters and heart protectors.


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Studies in animals and in laboratory dishes suggest that oxidative stress contributes to diseases like cancer and heart disease, two diseases that together account for nearly half of all deaths in the U.S. If so, there’s reason to believe that antioxidants -- including beta-carotene, selenium, and vitamins A, C and E -- could be useful as preventive medicines.

But when the task force examined the medical evidence on vitamins, it found “inadequate evidence” to support the claims that vitamin and mineral supplements benefit healthy adults. Multivitamins, individual vitamins and minerals, and specifically beta-carotene and vitamin E all failed to show they could reduce the risk of heart disease or cancer in people with no nutritional deficiencies.

“Cardiovascular disease and cancer have a significant health impact in America, and we all want to find ways to prevent these diseases,” Dr. Virginia Moyer, who heads the task force, said in a statement. But so far, she added, the medical evidence does not show that taking vitamins is helpful in this regard.

However, the task force did find “adequate avidence” that people with an elevated risk for lung cancer -- including smokers and people who are exposed to asbestos at work -- actually increase their risk further by taking beta-carotene, a precursor of vitamin A.

Scientists at the Linus Pauling Institute at Oregon State University, who generally encourage Americans to take a daily multivitamin, agreed with the task force’s conclusions that beta-carotene could be harmful to people at high risk for lung cancer. They also agreed that beta-carotene and vitamin E aren’t helpful for warding off cancer or heart disease. However, they said the jury is still out on whether vitamin E has other health benefits.


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In addition, the Washington-based trade group that represents the makers of vitamin and mineral supplements emphasized that the task force’s conclusions only address the issue of cancer and heart disease prevention. Most Americans who take vitamins do so to maintain their overall health, and the report published Monday does not address that purpose, according to a statement from the Council for Responsible Nutrition.

The task force recommendations apply to healthy adults age 50 and older who don’t have “special nutritional needs.” The advice does not apply to children, women who are pregnant or may become pregnant, people with chronic illnesses, or people who have to take supplements because they can’t get all their essential nutrients from their diet.

Members of the task force noted that there just aren’t many randomized, controlled clinical trials that assess vitamins and multivitamins in groups of people that represent U.S. adults as a whole.

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