Long-term daily multivitamin use resulted in a modest but statistically significant reduction in cancer after more than a decade of treatment and follow-up, a study found.
Randomized trials of higher-dose individual vitamins and minerals for cancer have never shown an association, but people take them anyway for that purpose. So researchers analyzed data from nearly 15,000 participants age 50 or older from the Physicians' Health Study (PSH II) starting in 1997 with treatment and follow-up through June 2011.
Participants received a daily multivitamin or equivalent placebo. Results appeared in the Oct. 17 issue of the Journal of the American Medical Association.
Participants were followed for an average of 11.2 years. Men taking a daily multivitamin had less incidence of total cancer (multivitamin and placebo groups, 17.0 and 18.3 events, respectively, per 1,000 person-years; hazard ratio [HR], 0.92; 95% confidence interval [CI], 0.86 to 0.998; P=.04) compared to placebo.
There was no significant effect of a daily multivitamin on prostate cancer (multivitamin and placebo groups, 9.1 and 9.2 events, respectively, per 1,000 person-years; HR, 0.98; 95% CI, 0.88 to 1.09; P=.76), colorectal cancer (multivitamin and placebo groups, 1.2 and 1.4 events, respectively, per 1,000 person-years; HR, 0.89; 95% CI, 0.68 to 1.17; P=.39), or other site-specific cancers.
There was no significant difference in the risk of cancer mortality (multivitamin and placebo groups, 4.9 and 5.6 events, respectively, per 1,000 person-years; HR, 0.88; 95% CI, 0.77 to 1.01; P=.07).
Daily multivitamin use was associated with a reduction in total cancer among 1,312 men with a baseline history of cancer (HR, 0.73; 95% CI, 0.56 to 0.96; P=.02), but this did not differ significantly from that among 13,329 men initially without cancer (HR, 0.94; 95% CI, 0.87 to 1.02; P=.15; P for interaction=.07).
Researchers noted that total cancer rates were likely influenced by the increased surveillance for prostate-specific antigen and subsequent diagnoses of prostate cancer.
"Approximately half of all confirmed cancers in PHS II were prostate cancer, of which the vast majority were earlier stage, lower grade prostate cancer with high survival rates," they wrote. "The significant reduction in total cancer minus prostate cancer suggests that daily multivitamin use may have a greater benefit on more clinically relevant cancer diagnoses."
One important caveat: Naoto T. Ueno, MD, FACP, in practice at the MD Anderson Cancer Center in Houston, points out that "[T]his was studied in healthy people (no smoking, not too fat)."