Vitamin and Mineral Supplements Do Not Prevent Cancer or CVD

Ricki Lewis, PhD

November 13, 2013

Healthy people do not require vitamin and/or mineral supplements to prevent cancer or cardiovascular disease (CVD), according to an analysis of several studies that was published online November 11 in the Annals of Internal Medicine.

Nearly half the US population takes vitamin and/or mineral supplements, with the expectation that the products will prevent chronic diseases. The rationale is that CVD and cancers, the 2 leading causes of death, share the risk factors of inflammation, variant methionine metabolism, and oxidative stress and that micronutrients counter these problems.

Tests of individual nutrients in nonhuman animals and in vitro support the protection hypothesis, but results of larger studies do not bear this out. Therefore, in 2003, the US Preventive Services Task Force concluded that evidence was insufficient to recommend for or against antioxidant combinations; vitamins A, C, and E; and multivitamins with folic acid. The task force recommended against use of β-carotene because of evidence that it can increase the risk of developing lung cancer in some individuals. The current study updates and supports the 2003 recommendations.

Stephen P. Fortmann, MD, and colleagues from the Kaiser Permanente Center for Health Research in Portland, Oregon, consulted 26 studies conducted since the last review, delving deep into meta-analyses, bibliographies, and government Web sites. They considered studies that evaluated vitamins A (including β-carotene), B1, B2, B6, B12, C, D, and E and calcium, zinc, iron, niacin, magnesium, selenium, and folic acid.

The studies analyzed the micronutrients singly, in pairs, and in more complex combinations. The researchers assessed primary prevention of CVD and cancer, as well as all-cause mortality not resulting from these conditions. The populations were community-dwelling healthy adults taking less-than-toxic doses of the supplements.

After rigorous analysis of the quality of the studies, the researchers focused on 5 trials that included 100,944 participants, concluding that "[m]ultivitamins had no effect on fatal and nonfatal CVD events overall."

One study found that multivitamins reduced overall cancer incidence after 11.2 years, but other studies did not confirm this finding. The literature search did not find consistent evidence of harm from supplements, except for the well-established association of β-carotene with lung cancer.

The lack of a protective effect was seen in studies on single nutrients, as well as in broader investigations that tested multivitamin supplements. The researchers did identify 2 multivitamin trials that detected a "borderline significance" for cancer, but the trials evaluated only men.

The investigators hypothesize that this discordance between the assumption that taking supplements protects against disease and consistent findings that this is not the case could be a result of effects on physiology of taking amounts of vitamins and minerals as supplements that perhaps do not replicate mixtures of micronutrients found in nature.

A major limitation of the study is that the trials examined tested different combinations of micronutrients in differing amounts on different populations of healthy individuals. However, the investigators caution that further research is necessary to establish the value of supplements.

The authors have disclosed no relevant financial relationships.

Ann Intern Med. Published online November 11, 2013. Full text

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