(ChemotherapyAdvisor) – Daily multivitamin use is associated with a modest but statistically significant reduction in total cancer risk for men older than age 50 years, including among men with a history of prior cancer diagnoses, according to results from the randomized, placebo-controlled Physicians’ Health Study II, presented during the 11th Annual AACR International Conference on Frontiers in Cancer Prevention Research.

The study was published October 17 in JAMA, the Journal of the American Medical Association.

“In this large-scale, randomized, placebo-controlled trial among middle-aged and older men, long-term daily multivitamin use had a modest but statistically significant reduction in the primary end point of total cancer after more than a decade of treatment and follow-up,” reported lead authors J. Michael Gaziano, MD, MPH, and Howard D. Sesso, ScD, PhD, of Brigham and Women’s Hospital and Harvard Medical School in Boston, Massachusetts.

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During a median follow-up period of 11.2 years, 2,669 study participants were diagnosed with confirmed cancers, including 1,373 cases of prostate cancer. Multivitamin use was associated with a significantly lower incidence of total cancer compared to placebo (17.0 vs 18.3 diagnoses per 1,000 person-years; HR, 0.92; 95% CI, 0.86-0.998; P=0.04).

The results were more modest than the cancer-prevention benefits associated with not smoking tobacco, exercise, and a healthy diet.

There was no significant effect of daily multivitamin intake on prostate cancer (P=0.76) or other site-specific cancers. Total mortality was not reduced (P=0.13).

Among 1,312 study participants with a history of prior cancer diagnoses, total cancer incidence was significantly reduced among those assigned to the multivitamin arm of the study (HR, 0.73; 95% CI, 0.56-0.96; P=0.02). The effect “appeared stronger” among men with a history of prior cancers than men without previous cancer histories at baseline, but was not significantly greater than that observed among men without prior cancers (HR, 0.94; 95% CI, 0.87-1.02; P=.15), the authors reported.

However, “the effect of a daily multivitamin on total epithelial cancer was stronger among men with a history of cancer at baseline,” the authors noted (HR, 0.66; 95% CI, 0.50-0.88; P=0.004).

Men taking multivitamins were more likely than placebo-arm patients to have rashes (HR, 1.07; 95% CI, 1.01-1.14; P=0.03) and nose bleeds (HR, 1.10; 95% CI, 1.02-1.18; P=0.01), but were less likely to experience minor hematuria (HR, 0.91; 95% CI, 0.84-0.98; P=0.02).

“There was significant effect modification by parental history of cancer,” the authors noted. Men without parental histories of cancer benefited from multivitamin use (HR, 0.86, 95% CI, 0.76-0.98; P=0.02), they wrote, while men with parental histories of cancer did not (P=.37).

“There have been several (previous) large observational studies of long-term multivitamin use on the risk of total cancer and other site-specific cancers,” Dr. Sesso said. “The difference is that these are not clinical trials, and do not account for confounding.”