Daily supplementation with multivitamins modestly but significantly reduced the risk of cancer in healthy male doctors who took them for more than 10 years, according to the results of a study published in the Journal of the American Medical Association.

The chance of an individual developing cancer depends on both inherited genetic factors as well as environmental or behavioral factors. Dietary and lifestyle habits may play a role in the development of cancer and researchers continue to evaluate different foods and supplements and their relationship to different types of cancers. Identifying dietary factors related to cancer could lead to potentially preventive lifestyle habits and strategies.

There has been conflicting evidence regarding the relationship between vitamins and cancer risk, with many studies focusing on individual vitamins such as vitamin D, vitamin B, vitamin C, and calcium. Multivitamins are the most common dietary supplement—approximately one-third of all U.S. adults take them—but there has been little evidence for or against them.

Researchers conducted a large-scale, randomized, double-blind, placebo-controlled study called the Physicians’ Health Study II, which included 14,641 male physicians in the U.S. age 50 or older. The study began in 1997, with treatment and follow-up through June 2011. At the beginning of the study, 1,312 men had a history of cancer.

Participants in the study were randomized to receive a monthly package of multivitamins or placebo. The primary endpoint of the study was total cancer (excluding non-melanoma skin cancer) and secondary endpoints included prostate, colorectal, and other site-specific cancers.

After a follow-up of 11 years, there were 2,669 new cancer cases, including 1,373 cases of prostate cancer and 210 cases of colorectal cancer. The researchers found that the men taking multivitamins had about an 8 percent lower risk of developing cancer. Multivitamins, however, had no significant effect on prostate cancer, colorectal cancer, or other site-specific cancers. What’s more—there was no significant difference in the risk of cancer mortality among the multivitamin or placebo groups.

The researchers concluded that daily multivitamin supplementation was associated with a modest, but significant, reduced risk of total cancer. It’s important to note that multivitamins—or any supplements, for that matter—are not a panacea. Individuals may wish to take multivitamins to prevent nutritional deficiency, but should always consult with a physician regarding the best course of action. Some supplements are contraindicated for certain individuals. For example, individuals taking common heart medications should avoid vitamin K. Consult with a physician to choose dietary supplements that can help rather than harm.

Reference:

Gaziano JM, Sesso HD, Christen WG, et al. Multivitamins in the prevention of cancer in men: The Physicians' Health Study II Randomized Controlled Trial. Journal of the American Medical Association. Published early online October 17, 2012. doi:10.1001/jama.2012.14641

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