MULTIVITAMIN/MINERAL SUPPLEMENTS AND CANCER
Victoria Drake, Ph.D.
Multivitamin/mineral supplements (MVMs) are popular dietary supplements taken by about one-third of Americans. It is not yet known whether taking a MVM might prevent chronic or age-related disease; previous findings of observational studies and randomized controlled trials (RCTs) on MVM supplementation and disease have been mixed. Results from a new study—the largest and longest RCT to date—indicate that MVMs offer older, well-nourished men some protection against cancer, suggesting that a healthy diet alone may not be sufficient to meet micronutrient needs for health promotion in this population.
The new Harvard study, the Physicians’ Health Study II (PHS II), examined the effect of MVMs on the primary prevention of cancer, cardiovascular disease, age-related eye diseases, and early cognitive decline. In this trial, 14,641 male physicians (50 years or older at the beginning of the study; mean age of 64.3 years) were randomized to receive either a daily MVM or placebo; the men did not know which supplement they received. Men with a history of cancer, heart attack, or stroke at the time of study enrollment were not excluded from the study. Participants were followed for an average of 11.2 years.
Most notably of the PHS II results, MVM supplementation lowered the incidence of, that is, reduced the risk for overall cancer by 8% (total cancers excluding nonmelanoma skin cancers); this effect was stronger in men aged 70 years or older and in men with no parental history of cancer. Additionally, MVMs reduced overall cancer occurrence in men who had a personal history of cancer at the time the study began (1,312 of the study participants). Statistical power was limited to detect an effect of MVMs on the incidence of individual cancers, but excluding cases of prostate cancer from total cancers resulted in a significant, 12% reduction in cancer risk. Furthermore, PHS II found a nonstatistically significant trend for a 12% decreased risk for cancer mortality. MVM use in the PHS II, however, did not reduce risk for cardiovascular disease or total mortality in older men.
Thus, the major finding of PHS II is that MVM supplementation reduced risk of total cancers. While an 8% reduction in risk is modest, such a decrease would have public health significance, possibly preventing up to 130,000 cases of cancer each year in the U.S. alone. It is important to note that the PHS II trial was conducted in a group of well-nourished, older physicians with a lower than average fraction of current smokers (<4% of study participants). Therefore, MVMs appear to offer added benefit in a healthy population of older men. It is possible that some groups of people, such as those with high-stress jobs, have higher requirements for vitamins and nutritionally essential minerals, and a healthy diet alone may be insufficient for health promotion in such populations.
Previous research on MVM supplementation and chronic disease, mainly from observational studies, has been inconsistent. The PHS II trial is the largest and longest double-blind, placebo-controlled trial of MVM supplementation to date. While both observational studies and RCTs have inherent limitations, RCTs are considered the “gold standard” in medicine and are the only type of study that can establish causation; observational studies can only show associations that may or may not be causally linked. One of the largest observational studies looking at MVM supplementation, the Women’s Health Initiative in 2009 that followed 93,676 women for 7.9 years, found little difference in total mortality or in the incidence of cancer or cardiovascular disease between women regularly taking MVMs and those who did not. A large-scale RCT in women is needed to determine whether long-term adherence to a MVM might have benefits similar to those reported for men.
In summary, the PHS II found a modest but significant cancer preventive effect of MVMs in older men, especially the elderly, and noted a trend for decreased cancer-related mortality in men taking the MVMs. Few adverse side effects were reported, and the safety of MVMs that provide the daily values (DV) of micronutrients (i.e., not megadoses) is generally well recognized. It’s important to note that the MVM used in PHS contained 25 micronutrients, most at levels at or below the DV. The benefits observed in this study might be larger in a less well-nourished population suffering from micronutrient inadequacies. While such dietary supplements appear to offer added benefit, a healthy diet, maintaining a healthy weight, regular exercise, and avoiding tobacco remain critically important for the prevention of cancer and other chronic diseases.
Last updated May 2013