Two studies included in the review found lower overall cancer incidence in men who took a multivitamin for over 10 years. Those same studies showed no cancer protection benefit for women. Researchers caution that these results should not be overgeneralized and that more research is needed before it can be determined whether or not multivitamin supplementation is beneficial.
The evidence review was conducted by researchers for the United States Preventive Services Task Force (USPSTF) to update its previous recommendation. In 2003, the USPSTF found insufficient evidence to recommend for or against the use of vitamins A, C, and E, multivitamins with folic acid, or antioxidant combinations for the prevention of CVD or cancer. At the time, the USPSTF recommended against beta-carotene supplements alone or in combination with other supplements because they had no benefit and actually harmed patients at risk for lung cancer. The current research review reconfirmed the beta-carotene findings and also found good evidence that vitamin E does not protect against cancer or cardiovascular disease.
In response to the review, industry trade associations offered their analysis.
“Cancer is a complex disease, and the fact that there is even some, albeit limited, evidence that a simple multivitamin could prevent cancer demonstrates promise and should give consumers added incentive to keep taking their multivitamins,” said Duffy MacKay, ND, Vice President, Scientific and Regulatory Affairs, CRN. “As the researchers have indicated, there is limited evidence for multivitamins in preventing cancer or cardiovascular disease; however, we believe the paucity of clinical trial evidence should not be misinterpreted as a lack of benefit for the multivitamin. We know for sure that multivitamins can fill nutrient gaps, and as so many people are not even reaching the recommended dietary allowances for many nutrients, that’s reason enough to add an affordable and convenient multivitamin to their diets.
“Further, given the encouraging results from the Physicians’ Health Study (PHS) II (Gaziano et al, 2012)—the study referenced in this report as demonstrating benefit for multivitamins and cancer risk in men—academics and government, as well as our own industry, should continue to support and fund research to clarify this relationship and to determine additional benefits for vitamins and other dietary supplements.
“In reviewing the scientific literature, the authors reaffirmed the overall safety for the multivitamin, noting there was ‘…no consistent pattern of harm from nutritional dosages of multivitamins’ but identifying a few studies for a few individual nutrients that pointed to some risk. They also debunked concerns raised by some researchers about calcium and cardiovascular disease, noting that while additional research should further examine this question, available studies did not show consistent findings for concern.
“We commend the authors of this systematic review for noting that trials designed to evaluate drug therapy ‘…might not be ideally suited to evaluating nutrients’ as this confirms what many in the nutrition science community have focused on for years. Nutrients work in synergy with other nutrients, and likely also in combination with other lifestyle choices, such as exercise and proper sleep. We should consider vitamins a piece of the health puzzle, not magic bullets that are the be-all and end-all for preventing serious diseases like cancer and cardiovascular disease. Multivitamins fill in nutrient gaps from our less-than-perfect diets and support a host of other physiological functions. If there are benefits for vitamins for cancer and cardiovascular disease, those benefits are icing on the cake.”
The Natural Products Association (NPA) also defended dietary supplements in response to the review.
Cara Welch, Ph.D., Senior Vice President of Scientific and Regulatory Affairs, said “The scope of this analysis certainly has its limitations. The meta-analysis focused on studies that researched generally healthy people, avoiding any instances for targeted use of nutrients. Additionally, the researchers only concentrated on studies with vitamins and mineral supplements as the primary source of prevention. Multivitamin supplements should not be expected, without the combination of a healthy lifestyle, to prevent chronic disease. The results of this review should not lead to widespread concern among consumers who take vitamin and mineral supplements.”
John Shaw, Executive Director, noted, “Dietary supplements are used by more than 150 million Americans on a daily basis. Research has shown that when taken in combination with other healthy lifestyle practices, such as consuming a wholesome diet and exercising regularly, people can benefit from dietary supplements. Consumers should be comfortable following a variety of healthy habits, which includes supplementation. As always, NPA encourages consumers to speak with their healthcare professionals regarding their dietary supplement regimen.”