Writing in the Annals of Internal Medicine, the USPSTF researchers noted that two trials have both found that multivitamin use may lower the overall incidence of cancer in men, but the overall data is insufficient to confirm that multivitamin supplementation is beneficial.
“The results of vitamin supplementation trials have been disappointing at best, despite having a solid mechanistic basis,” wrote the authors, led by Stephen Fortmann, MD, from Kaiser Permanente Center for Health Research.
“One explanation for this result could be that the physiologic systems affected by vitamins and other antioxidant supplements are so complex that the effects of supplementing with only 1 or 2 components is generally ineffective or actually does harm.
“This hypothesis is compatible with our finding that the best support for benefit of supplementation came from 2 multivitamin trials that used physiologic doses of a wider variety of agents.”
In a nutshell
The systematic review, which included 26 trials (24 RCTs and 2 cohort studies), found that, while there was inconsistent evidence to show that supplements influenced the risk of CVD, cancer, or all-cause mortality in healthy adults without nutritional deficiencies, “the certainty of this result is tempered, however, by the fact that few fair- or good-quality studies”.
Dr Fortmann and his co-workers did consider the evidence for vitamin E to be robust enough to conclude that there are no benefits for this nutrient. In addition, the review also confirmed previous findings that beta-carotene supplementation may increase the on lung cancer for people already at high risk of this particular disease like smokers.
The dietary supplements industry was quick to comment on the review’s findings, with Cara Welch, PhD, Senior Vice President of Scientific and Regulatory Affairs, for the Natural Products Association (NPA), noting that limitations in the scope of the analysis.
“The meta-analysis focused on studies that researched generally healthy people, avoiding any instances for targeted use of nutrients,” said Dr Welch. “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.”
‘Vitamins a piece of the health puzzle, not magic bullets’
Duffy MacKay, ND, vice president, scientific and regulatory affairs, for the Council for Responsible Nutrition (CRN), said that 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.
“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,” he said.
“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.
Dr MacKay added that the authors reaffirmed the overall safety for the multivitamin, noting there was ‘…no consistent pattern of harm from nutritional dosages of multivitamins’.
“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,” he added.
“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,” said Dr MacKay. “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.”
Source: Annals of Internal Medicine
December 2013, Volume 159, Number 12, doi:10.7326/0003-4819-159-12-201312170-00729
“Vitamin and Mineral Supplements in the Primary Prevention of Cardiovascular Disease and Cancer: An Updated Systematic Evidence Review for the U.S. Preventive Services Task Force”
Authors: S.P. Fortmann, B.U. Burda, C.A. Senger, J.S. Lin, E.P. Whitlock