Scientists Debate Dietary Supplements, Cancer Risk

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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. 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.

The opening session of the AICR conference focused on complexities associated with studying the effects of supplement use on cancer risk.

Other topics to be discussed over the next two days include: Vitamin D; Diet and Cancer Survivors; the New Science of Epigenetics (How Diet Changes Gene Function); Probiotics; and the Study of Behavior Change.

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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 at very high amounts, may actually promote cancer.

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, Ph.D., 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.

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

Until research allows for more targeted advice, AICR recommends seeking cancer protection from a diet high in a variety of plant foods instead of relying on dietary supplements.

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