Cancer Journal Highlights Negative Supplement-Cancer Links

A review from a group of university-based researchers concluded there is little to no evidence dietary supplements can reduce cancer risk, but some supplements may actually increase cancer risk. In their article published in the May issue of the Journal of the National Cancer Institute (JNCI; 2012 May 16;104(10):732-9), the authors also blasted persistent anticancer marketing claims and "insufficient government regulation in the supplement industry.

Spearheaded by Maria Elena Martinez, Ph.D., Moores UC San Diego Cancer Center, the review of cancer risk studies involving antioxidants, folate and folic acid, vitamin D and calcium was conducted in conjunction with scientists from University of Arizona, University of North Carolina and Colorado School of Public Health. They said the review focused on trials supplements that have been tested in adequately powered clinical trials or in large well-designed observational studies

As Duffy MacKay, ND, VP of scientific and regulatory affairs fro Council Responsible Nutrition (CRN), noted, the paper's title, "Dietary Supplements and Cancer Prevention: Balancing Potential Benefits Against Proven Harms," gives the impression dietary supplements have proven to be harmful, which is not proven. "There may be theories or evidence," MacKay said, "but that doesn't equate to proof."

In fact, among the research cited by the paper as evidence of harmful supplements that may actually increase cancer risk include a 1996 study (N Engl J Med. 1996;334:1150-1155) that found a 39-percent increase in lung cancer incidence in high-risk lung cancer subjects (including those who smoke or have been exposed to asbestos) who also took beta carotene (30mg/d); and a 2007 JAMA study (297(21):2351-2359) that found folic acid supplementation (1 mg/d) increased the risk of having three or more adenomas and of noncolorectal cancers in men and women with a recent history of colorectal adenomas. Both of these studies, or at least the significance of their conclusions, have been questioned.

While promising epidemiological results, such as with beta-carotene-rich fruit and vegetable intake on lung cancer, have prompted larger, randomized clinical trials to investigate findings, there has been a lasting argument against studying an isolated nutrient on multi-factorial diseases in very high-risk populations.

"It's not surprising that folic acid alone may not prevent the recurrence of adenomas," said Andrew Shao, PhD., then VP of scientific and regulatory affairs for CRN and current VP of global product science and safety for Herbalife, about the JAMA folic acid study. "Perhaps in combination with other related nutrients or in subjects without previous adenomas we would have seen more promising results, confirming what was suggested from earlier research."  

CRN and other nutrition-minded groups expressed a concern studies like these would scare the public from ensuring adequate intake of these nutrients, including through the use of supplements, as each nutrient has been shown to offer important health benefits in areas other than cancer. MacKay noted there are many challenges in studying isolated nutrients in the randomized controlled trial (RCT) format, including the near impossibility of having a true placebo group. For instance, he said it would be unethical to knowingly keep a group in a state of vitamin deficiency for the duration of a long-term RCT.

The other issue nutrition advocates cited with the current JNCI trial is with the policy statements made by the authors: "Despite this evidence, marketing claims by the supplement industry continue to imply anticancer benefits. Insufficient government regulation of the marketing of dietary supplement products may continue to result in unsound advice to consumers. Both the scientific community and government regulators need to provide clear guidance to the public about the use of dietary supplements to lower cancer risk."

However, the authors do seem to maintain some chance for dietary supplements on cancer, citing the need for additional RCTs on the subject. "... but these trials must be designed strategically and in light of lessons learned from previous studies," they wrote. "In the absence of convincing evidence that more will be better, we probably do not need more trials in nutrient-replete populations."