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ucsdhealthsciences:

In pill health

Half of all American adults take one or more dietary supplements, mostly multivitamins. Selling these supplements is a $30 billion-a-year industry in the United States, comparable to the National Institutes of Health’s entire budget for all medical research.

Yet, with very few exceptions, nutritional deficiencies in the United States are rare. Americans might not necessarily eat right, but they are not nutritionally deprived.

So why do most people take them? Their answer: “They’re healthy. They can’t hurt.”

Most people are wrong.

In a recent commentary in the Journal of the National Cancer Institute, Maria Elena Martinez, PhD, a professor in the department of Family and Preventive Medicine at the UC San Diego School of Medicine and Co-leader of the Reducing Cancer Disparities program at the Moores UCSD Cancer Center, and colleagues discuss the benefits and risks of dietary supplements, particularly when taken to “prevent cancer.”

Their conclusion, after reviewing existing scientific literature on the subject: There is little empirical evidence to support the widely held and widely advertised notion that popular supplements like beta-carotene, folic acid, vitamin D and calcium reduce cancer risk.

Indeed, the opposite may be true.

That’s not what people want to hear, of course. Axioms like “an apple-a-day” and “we are what we eat” have a sort of enduring resonance. They may be true, write Martinez and colleagues in their JNCI paper, but the nutritional supplement industry exploits it to excess, suggesting in often misleading fashion that if a little bit of a nutrient is good, then a lot must be better.

This is not just another case of economic exploitation in the marketplace. While there is little compelling evidence that nutritional supplements significantly prevent cancer, there is growing proof that too much might cause it.

For example, some studies have found that exogenous or added antioxidants like beta-carotene might, in fact, promote oxidative stress linked to carcinogenesis. Other trials have found that long-term folic acid supplementation boosts the risk of colorectal tumor growths. Several observational studies support an association between higher calcium consumption and reduced breast cancer risk, but higher calcium intake also appears to increase the chances of contracting prostate cancer.

The situation is, in a word, confounding. The observational studies that nutritional supplement-makers most often cite as evidentiary proof (along with testimonials utterly bereft empirical value) are inherently limited. They lack the standardized treatment regimens and controls required to scientifically prove or disprove efficacy and safety. They have value in terms of involving large numbers of test participants – the proverbial big picture – but the devil is usually in the details: Cancer risk is different in different tissues. Personal characteristics, from genetics to behaviors, are massively influential. What is the effect, for example, of taking many supplements at once? How do they interact with each other? How well do they work if the person is a smoker, drinker, obese or all three?

These are factors that must be – and are – addressed in the gold standard of scientific experimentation: the randomized controlled trial (RCT), which is rigorously designed to produce precise data without bias. Unfortunately, RCTs of nutritional supplements are relatively few in number, and their conclusions thus far have been mixed.

Cancer does not give up its secrets easily. RCTs are expensive. It often takes decades for cancer to manifest itself, much longer than most RCTs attempting to reveal the cancer prevention benefits or cancer-causing dangers in nutritional supplementation.

Nonetheless, Martinez and colleagues argue in their commentary that more, longer and better-designed RCTs are needed, indeed essential to determining the benefits and risks of supplements.

In the meantime, they call for improved oversight of the manufacture and marketing of dietary supplements, which has a short and sketchy history of regulation. The U.S. Food and Drug Administration only began attempting to regulate these substances in the 1960s. Its efforts have been significantly and repeatedly constrained by a well-funded supplement industry and its political advocates.

Today, dietary supplements exist in a sort of legal limbo somewhere between foods and drugs. Manufacturers cannot make bold, direct assertions of cancer prevention benefits. The high-profile deaths from the supplement ephedra helped end that, but they can – and do – advertise the cancer prevention powers of supplements by implication.

Take Pill X, which research has been found to reduce the growth of prostate cells in culture. Makers of Pill X advertise that it “supports prostate health.” They cite stories of real people who took Pill X and didn’t get prostate cancer. For the casual consumer, it’s easy to conclude that Pill X has anticancer properties, despite the lack of any real science to support that conclusion.

Of course, maybe Pill X does reduce cancer risk – and maybe it increases it. No one knows. The scientific data are lacking. Think about that next time you take a nutritional supplement you probably don’t need.