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Vitamin supplements: Experts find no evidence that they prevent heart disease or cancer

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The review found that except for two clinical trials that reported “a small borderline-significant benefit” from multivitamin supplements on cancer (but only in men), there was no evidence that supplements had any effect on reducing the risk of heart disease, cancer or early death in the general public.

Yet another group of medical experts has found no evidence that taking vitamin and mineral supplements will protect against the two leading causes of death in the United States: heart disease and cancer.

In fact, the U.S. Preventive Services Task Force (USPSTF), an independent panel that assesses the scientific evidence for a variety of preventive health services, has concluded that taking supplements of one vitamin, beta-carotene, may actually increase the risk of developing lung cancer, particularly among smokers.

The USPSTF made these statements in a new draft of recommendations released Tuesday. The recommendations, when finalized, will update ones issued by the task force in 2003.

Those earlier recommendations had also found insufficient evidence that vitamin and mineral supplements (either alone or in various combinations) prevented heart disease or cancer.

The major change in the new recommendations is the finding that vitamin E supplements offer no benefit for the prevention of cardiovascular disease or cancer. The earlier recommendations had simply stated that the evidence was inconclusive.

A comprehensive review

The USPSTF based its recommendations on a comprehensive evidence review led by a team of researchers at the Kaiser Permanente Center for Health Research in Portland, Ore., and published Tuesday in the Annals of Internal Medicine. The new review looked at a variety of vitamins and minerals, including several that had not been included in the 2003 USPSTF recommendations — most notably, vitamin D, calcium, selenium and folic acid.

The review found that except for two clinical trials that reported “a small borderline-significant benefit” from multivitamin supplements on cancer (but only in men), there was no evidence that supplements had any effect on reducing the risk of heart disease, cancer or early death in the general public.

“The results of vitamin supplementation trials have been disappointing at best,” state the authors of the review.

The disappointment stems from the fact that animal and other laboratory studies have suggested that vitamin and mineral supplements might reduce the oxidative stress and inflammation associated with the development of cardiovascular disease and cancer.

But that hypothesis has not been supported by the findings of large clinical trials.

(Vitamin supplements do, of course, help people with a specific diagnosed nutritional deficiency, such as Wernicke-Korsakoff disease or pellegra. And folic-acid supplements taken by women during pregnancy have been shown to prevent neural-tube birth defects in newborns.)

In step with other groups

The new USPSTF recommendations support those by other health organizations. The American Heart Association, for example, believes that “healthy people [should] get adequate nutrients by eating a variety of foods in moderation, rather than by taking supplements.”

The National Cancer Institute agrees. It notes on its website that clinical trials have found no evidence that supplements are beneficial in preventing cancer or in helping individuals who have been diagnosed with the disease.

Getting people to heed such recommendations and warnings has proven difficult, however. As the USPSTF points out, almost half of adults in the United States take at least one dietary supplement, mostly multivitamins. The annual national price tag for those supplements in 2010 was $28.1 billion.

You’ll find the USPSTF’s draft recommendations on its website. You can also read the review analysis in full at the Annals of Internal Medicine website.

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