Scientists Address Lingering Questions On Dietary Supplements And Cancer Risk

Main Category: Cancer / Oncology
Also Included In: Nutrition / Diet
Article Date: 09 Nov 2008 - 0:00 PST

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Today, at the annual research conference of the American Institute for Cancer Research (AICR), a panel of leading scientists discussed the state of the evidence on dietary supplements and their effects on cancer risk.

Dietary supplements are a $22 billion industry in the US; every day, millions of Americans avail themselves of vitamin, mineral or herbal supplements in an effort to boost their health. Yet last November, an AICR expert report reviewed the evidence and concluded that, when it comes to cancer, dietary supplements can be either protective or harmful.

In fact, because high-dose supplement use has been linked to increased cancer risk in some groups, the AICR experts concluded: "Don't use supplements to protect against cancer." (The report took care to note, however, that some segments of the population may obtain other health benefits from supplements, including women who are or may become pregnant and the elderly.)

The opening session of the AICR conference in Washington, DC focused on several complexities associated with studying the effects of supplement use on cancer risk. John A. Milner, PhD, chief of the Nutritional Science Research Group, Division of Cancer Prevention at the National Cancer Institute chaired the session.

Genetics Influence Effects

More human trials into the effects of supplements are sorely needed, for both cancer survivors and the general population, said Mary Frances Picciano, PhD, of the National Institutes of Health Office of Dietary Supplements.

"Not everyone responds to dietary substances in the same way because each person has a different genetic makeup," she said. Individuals differ, and so do products -- even the same supplements can vary from brand to brand, depending on methods of harvesting and manufacturing, which makes studying their effects even more difficult.

Folate: Dosage Size Matters

Folic acid, a B vitamin, is one nutrient used to fortify many different foods. Joel Mason, MD, of Tufts University, reviewed several studies showing folic acid to be associated with lower risk for some cancers.

But the vital question now before scientists, he said, is: How much is too much? Like several other vitamins, there is evidence that folic acid may be protective in moderate doses, but when consumed in very high amounts, may actually promote cancer.

Omega-3's: From Fish or Pills?

The AICR report concluded that getting nutrients from whole foods rather than dietary supplements is best, and one AICR grantee presented data suggesting a reason why. Robert S. Chapkin, PhD, of Texas A&M University, specializes in research on omega-3 fatty acids in fish. He said they may work together with dietary fiber to "superactivate the system," and increase cancer protection in the large intestine by triggering a response that attacks damaged cells.

Beyond Antioxidants

A protective set of reactions occur in the body when phytochemicals from broccoli (isothiocyanates) and garlic (organosulfur compounds) are eaten. Shivendra V. Singh, PhD, of the University of Pittsburgh discussed evidence indicating that these substance are more than just antioxidants - under certain conditions they exhibit pro-oxidant effects in ways that seem to specifically target tumor cells.

More, Better Research Needed

From The Netherlands, Ben van Ommen, PhD, of TNO Quality of Life said most micronutrients have overlapping or interacting activities in the body. For example, antioxidant vitamins interact with niacin, B12 and folate.

Studying how they work with each other, and finding out why some people might be vulnerable to too much of them, is essential, he said. "The current [research] methodology…is simply inadequate, and this results in many assumptions [that aren't proven]," he said. Determining how individuals' genetic variations are related to the efficacy of micronutrients is the big next step, he added.

Until further research allows for more targeted advice, AICR stands by its recommendation to seek cancer protection from a diet high in a variety of plant foods instead of relying on dietary supplements.

The American Institute for Cancer Research (AICR) is the cancer charity that fosters research on the relationship of nutrition, physical activity and weight management to cancer risk, interprets the scientific literature and educates the public about the results. It has contributed more than $86 million for innovative research conducted at universities, hospitals and research centers across the country. AICR has published two landmark reports that interpret the accumulated research in the field, and is committed to a process of continuous review. AICR also provides a wide range of educational programs to help millions of Americans learn to make dietary changes for lower cancer risk. Its award-winning New American Plate program is presented in brochures, seminars and on its website, http://www.aicr.org. AICR is a member of the World Cancer Research Fund International.

American Institute for Cancer Research