The study is being simultaneously published in the Journal of the American Medical Association.

"More than half of Americans take some kind of vitamin supplement, and the most commonly taken is a multivitamin," said John Michael Gaziano, M.D., chief of the Division of Aging at Brigham and Women's Hospital and a researcher at VA Boston. "No one has ever done a long-term trial to determine the potential health benefits or downsides of taking a multivitamin for a long period of time."

Gaziano and colleagues investigated the long-term effects of daily multivitamin use on certain site-specific cancers and total cancer occurrence and mortality. They used data from the Physicians' Health Study II, which included 14,641 male physicians aged 50 or older from the United States.

Researchers randomly assigned participants to a multivitamin or no multivitamin between 1997 and June 2011. During the median follow-up of 11.2 years, researchers recorded 2,669 cancer cases, including 1,373 prostate cancer cases and 210 colorectal cancer cases.

When examining outcomes at the study's end, the researchers found an 8 percent reduction in total cancer occurrence among participants assigned to multivitamin use.

"We also saw trends for some of the major site-specific cancers, though the numbers were small and not significant," Gaziano said. "There also seemed to be a greater effect in people with previous cancer."

Although prostate cancer was the most commonly occurring cancer in this population, there was no direct effect of multivitamin use on prostate cancer occurrence. However, when the researchers looked at the effect of a multivitamin on other site-specific cancers, they found about a 12 percent reduction in occurrence, according to Gaziano. Additionally, they saw a nonsignificant 12 percent reduction in cancer mortality.

"There are reasons to take a multivitamin even in our adult population, who are seemingly well nourished, as a way to get recommended daily amounts of vitamins and minerals," Gaziano said. "This study suggests, at least for men, that there might be benefits to taking multivitamins in terms of cancer as well."

Gaziano emphasized that the effects were modest and that multivitamin use should only be considered in addition to other habits, such as stopping smoking and increasing exercising, which literature has shown are effective in preventing cancer and other diseases.

Gaziano and colleagues plan to follow this population to determine if this effect strengthens over time. In addition, more studies on multivitamin use are needed in women.

Note: If no author is given, the source is cited instead.

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