A large study of older doctors shows that those who took a daily multivitamin had an 8% lower risk of cancer compared to those who took a placebo pill. The men in the study were followed for over a decade as part of the Physicians’ Health Study II. Results of the study were presented at the annual American Association for Cancer Research (AACR) International Conference on Frontiers in Cancer Prevention Research and published in JAMA.

This is one of the largest and longest studies addressing the health benefits of vitamin use. The study is also the first long-term study to assess the health effects of a daily multivitamin, according to the study's lead author, J. Michael Gaziano, MD, chief of the Division of Aging at Brigham and Women’s Hospital. The researchers plan to follow the study cohort over time to understand the even longer-term effect of multivitamins.

Multivitamins were associated with a reduced cancer risk

Approximately one-half of adult Americans take some sort of vitamin supplement. The most common type of supplement is a multivitamin, taken by at least one-third of adults in the United States. Previous studies of long-term vitamin use have been inconsistent in identifying a benefit in terms of cancer outcomes. Most studies have tested a single or small number of high-dose vitamins and minerals rather than a multivitamin and none have demonstrated a benefit in terms of cancer incidence. Of the studies that tested the role of a multivitamin on a specific cancer, the results range from a protective benefit, no link, and even a harmful effect. Another large, 15-year study of 88,756 nurses showed a decreased colon cancer risk among those who took a multivitamin.

The Physicians’ Health Study II randomized 14,641 male US physicians 50-years old or older to either a daily multivitamin or placebo starting in 1997. The median follow-up was 11.2 years with 2,669 total cases of cancer recorded. The most frequent cancer type was prostate, found in 683 in the multivitamin arm and 690 in the placebo arm.

Men taking a daily multivitamin had a statistically significant reduction in total cancer incidence (hazard ratio = 0.92, P = .04). When the results were analyzed for specific cancers, no link between any cancer type, including prostate and colorectal cancer, was found. No significant difference in cancer mortality was seen between the two study arms.

A total of 1,312 men in the study had a history of cancer at randomization. Among these men, a daily multivitamin was associated with a reduction in total cancer (hazard ratio = 0.73, P = .02), but the results were similar to those of the 13,329 men who did not have a history of cancer. Overall cancer mortality was numerically different, 403 men in the multivitamin group died of cancer compared to 456 men in the placebo group, but not statistically different between the two groups (P = .07).

“I was not completely surprised [by the results] because it was a multivitamin of relatively low doses of each of its components, and over 30 separate vitamins and minerals were included,” said Demetrius Albanes, MD, senior investigator at the nutritional epidemiology branch of the National Institutes of Health, who was not involved with the current study. According to Albanes, the result that prostate cancer incidence does not appear to be impacted by multivitamin use is of interest and should be further examined.

In their paper, Gaziano and authors postulate that the overall reduction in cancer risk seen in this study may be due to the “broader combination of low-dose vitamins and minerals contained in the multivitamin rather than an emphasis on previously-tested high-dose vitamins and minerals trials, may be paramount for cancer prevention.”

One limitation of the current study is that the participants were all well-nourished, relatively healthy men for whom the effect of a multivitamin may be more pronounced compared to less well-nourished populations. Assessing how a baseline nutritional status affects health outcomes for those who take a daily multivitamin should be addressed in future studies.

Albanes is not aware of other large-scale multivitamin cancer prevention trials, but believes that there will be some in the near future, particularly for women, who were not included in the current study.