Taking a daily multivitamin for years may lower the risk of cancer, according to new research.
The study followed nearly 15,000 middle-aged and older men for about 11 years. It is not yet clear if the findings would apply to women or younger men.
"The main findings were a reduction in total cancers of 8%,'' says researcher J. Michael Gaziano, MD, MPH, a researcher at Brigham and Women's Hospital and Harvard Medical School.
''Our main message is that the main reason to take a multivitamin is to prevent nutritional deficiency,'' Gaziano said at a news briefing today at an American Association for Cancer Research meeting held here.
"It appears there is a modest benefit for cancer reduction in men over 50," he said.
Vitamins and Cancer Risk: Details
The men were enrolled in the Physicians' Health Study (PHS) II. It studied the long-term effects of taking a multivitamin on the prevention of chronic disease, including cancer.
In the study, about half of the 15,000 men took a daily multivitamin, Centrum Silver. The other half took placebo. When they started the study, they were 50 or older.
At the start, 1,312 men had a history of cancer, but none had active cancer.
The researchers tracked the men to see who developed cancers, except non-melanoma skin cancers.
Cancer by the Numbers
In the vitamin group, there were 1,290 cancers. In the placebo group, there were 1,379.
About half of the cancers in each group were of the prostate.
Those diagnoses, the researchers say, were probably influenced by the increase in screening for prostate cancer during the study.
Most of the prostate cancers were earlier stage, with high survival rates.
When the researchers looked at cancers overall, they found the 8% reduction. No effect of a vitamin was found on prostate cancer by itself.
When the researchers separated out the prostate cancers, they found a 12% reduction in the incidence of all other cancers.
The researchers found no differences in the risk of death from cancer between the groups.
Health behaviors that could affect cancer risk, such as smoking and exercise, were evenly divided between groups, Gaziano says.
Vitamins and Cancer Risk: Explaining Vitamin Effects
The study is the first large-scale study of multivitamins and cancer prevention, Gaziano says.
Earlier research focusing on high doses of specific vitamins, and their effects on cancer prevention, have had mixed results. Some have shown possible harm. The researchers can't explain the anti-cancer effect they found with a multivitamin. "We don't know exactly how it works," says researcher Howard Sesso, ScD, MPH, an epidemiologist at Brigham and Women's Hospital and Harvard Medical School.
The combination of vitamins and minerals may mirror the ingredients in a healthy, plant-based diet, the researchers say.
How long does it take for the cancer prevention effect to kick in?
"It looks like you need to take a multivitamin for several years if not a decade," Sesso says, based on the study findings.
The researchers will report their study findings of the effects of vitamins on cardiovascular disease and other diseases later this year.
The researchers received research funding from the National Institutes of Health. They received vitamins or support from BASF Corporation, Pfizer, and DSM Nutritional Products Inc.
Vitamins as Cancer Fighters: Perspectives
The study helps clarify the potential role of multivitamins for cancer prevention, says Susan Gapstur, PhD, MPH, vice president of the American Cancer Society's epidemiology research program.
"Results of previous trials of vitamin and or mineral supplementation for cancer prevention have been mixed, and some studies of individual nutrients have shown evidence of possible harm," she says.
She also cautioned that the trial, although large, is just one study. "Typically, we like to see these kinds of findings replicated by other studies, and in other populations, before coming to solid conclusions."
The American Cancer Society recommends getting nutrients from a healthy diet. For those who choose a supplement, the best choice is a balanced multivitamin containing no more than 100% of the Daily Value of most nutrients, Gapstur says.