Dietary supplements — whether containing vitamins, minerals, herbs, amino acids or botanicals — have not been found to reduce the risk of cancer. In fact, the evidence now suggests that high doses of supplements may actually increase cancer risk.
That’s the conclusion — and the clear warning — of a commentary published Wednesday in the Journal of the National Cancer Institute (JNCI) by a team of U.S. scientists.
Yet, as the authors of the commentary also point out, getting people to understand that taking dietary supplements is not only unnecessary in most cases, but also potentially dangerous, is extremely difficult. There are two key reasons for this uphill battle: the relentless marketing efforts of the $30-billion-a-year supplement industry and the lack of any meaningful government regulation of that marketing.
Well, three reasons, actually. For the commentary also talks about how consumers often resist accepting the scientific evidence against supplements.
As a result, at least half of Americans take some kind of dietary supplement, mostly vitamins and minerals.
A detailed look at the research
The commentary’s authors, led by Maria Elena Martinez of the University of California San Diego Moores Cancer Center, summarize the cancer-related research to date on folic acid, vitamin D, calcium and various antioxidants (such as beta-carotene and vitamins A, E and C). The summary does a good job of explaining how and why people have come to mistakenly believe that supplements are good for them.
For example, observational studies have found that eating lots of fruits and vegetables is associated with a lower risk of certain cancers, especially lung and colorectal cancer. Since fruits and vegetables are high in antioxidants, scientists wondered if taking supplements of those nutrients would have a similar effect. Clinical trials followed. None of those studies, however, produced any convincing evidence that antioxidant supplements, either given individually or in combination, have any effect on reducing cancer risk.
In fact, write Martinez and her colleagues, “some clinical trials show that some of these antioxidant nutrients may increase cancer risk.”
Researchers now believe that the anti-cancer benefit conferred by fruits and vegetables is much more complex than a handful of nutrients.
Why regulations are weak
The authors of the commentary also describe how the supplement industry — helped by its congressional friends, especially Sen. Orrin Hatch, R-Utah — has successfully fought off any meaningful attempts to regulate not only the industry’s health claims, but also the safety of its products:
In 2010, in response to the continued need for better regulation of nutritional supplements, as evidenced by the problem of steroids being included without labeling in some sports supplements, US Senators John McCain and Byron Dorgan sponsored the Dietary Supplement Safety Act (DSSA), designed to give FDA the legal authority to monitor supplement safety and to withdraw from the market any deemed to be potentially hazardous to health. Again, fearing FDA encroachment into marketing, the powerful supplement industry protested; after an entreaty from Senator Orrin Hatch, a known supporter of the dietary supplement industry, Senator McCain, withdrew his support for the DSSA. More recent attempts to set guidelines for assessing supplement safety have also come under attack by the industry, even though some experts argue that those guidelines do not go far enough.
So the deceptive marketing continues:
In 2009, even after publication of the null findings from SELECT [Selenium and Vitamin E Cancer Prevention Trial], Bayer stopped advertising that its One-A-Day Men’s Health Formula supplement could prevent prostate cancer because it contained selenium and vitamin E only after it was threatened by a lawsuit. Perhaps, the most current direct evidence of this practice relates to vitamin D, which is being marketed in the popular media for its benefits in reducing cancers of the colon, breast, pancreas, and prostate. Even without such direct statements, anticancer effects can be implied.
For example, even though the manufacturers of Pill X cannot openly advertise that it prevents prostate cancer, they can create an advertisement that states that prostate cancer is a major health problem, that Pill X has a role to “support prostate health,” and that a particular study found that the compounds in Pill X reduced the growth of prostate cells in culture. Their website can then be accompanied by advertisements for Pill X and can contain links to testimonials that are free to expound the benefits of Pill X as experienced by real people. The absence of credible scientific evidence that taking Pill X confers anti-prostate cancer properties in men can be easily obscured by this constellation of claims that collectively suggest anticancer effects. As a result of limited regulatory authority, manufacturers who cannot overtly claim anticancer benefits of supplements without scientific proof are nonetheless free to imply those benefits in ways that make it difficult for the consumer to discern innuendo from scientific fact.
Unreasonable assumptions
No wonder the supplement business is booming. "Undoubtedly, use is driven by a common belief that supplements can improve health and protect against disease, and that at worst, they are harmless,” note Martinez and her colleagues. “However, the assumption that any dietary supplement is safe under all circumstances and in all quantities is no longer empirically reasonable.”
Yet, even when faced with the science, many Americans seem unwilling to acknowledge that they’re wasting their money — and perhaps putting their health at risk — by taking supplements, as the commentary’s authors point out:
Believers in supplements are sometimes quick to discredit caution over supplement use, as they suggest that the tendency of mainstream science to ignore nonconventional evidence is tainted or that mainstream science is somehow corrupted by its link to a medical-industrial complex that seeks to protect profits rather than prevent disease. Results of a recent survey showed that most US supplement users report that they would continue to use supplements even if scientific evidence found them to be ineffective or if the FDA specifically deemed them ineffective. Perhaps, it is generally assumed by supplement users that these products are as well regulated as over-the-counter medications.
“These beliefs underscore the need for efforts by scientists and government officials to encourage the public to make prudent decisions based on sound evidence with respect to use of dietary supplements for cancer prevention,” the scientists conclude.
Unfortunately, the commentary is behind a JNCI paywall. There's more than a bit of irony in that. For making these kinds of papers free to the public is one way scientists could help consumers be more prudent about their health decisions.