Magic Bullet Supplements Unlikely to Prevent Cancer

American Institute for Cancer Research
Monday, 6 March 2000

Cancer Researchers Stress that Interaction of Nutrients within Foods Offers Best Means of Protection

Concerned that the public may be misled by recent reports showing that isolated nutrients do not provide cancer protection, experts at the American Institute for Cancer Research (AICR) today stressed the interactive nature of cancer-fighting substances in fruits, vegetables, whole grains and beans. The vitamins, minerals and phytochemicals found in these foods work together in complex ways to fight cancer, researchers said.

In the last month alone, the findings of two single-agent studies have been widely reported. A Dutch study found no link between vitamins and dietary fiber upon stomach cancer. And according to a study in the Journal of the National Cancer Institute, beta-carotene pills afford no protection against cancer.

"The failure of these single-agent studies may cause people to lose sight of the central concept behind the research. That concept is synergy, by which different substances work together to produce a considerably stronger effect than they could individually," said Ritva Butrum, Ph.D., Vice-President for Research at AICR.

Trials focusing on single substances often show little or no protective effect. But the protective effects of such substances in combination with other compounds found in a healthy plant-based diet have been extensively documented.

An AICR report entitled Food, Nutrition and the Prevention of Cancer: A Global Perspective examined over 4,500 international studies on the link between diet and cancer. The report found convincing evidence that a predominantly plant-based diet rich in a variety of fruits, vegetables, whole grains and beans significantly reduces cancer risk.

Ultimately, researchers hope to determine how the many substances in these foods work in combination. After mapping out these important synergistic effects, they will be able to design healthy diets rich in foods that interact with each other for optimal disease-fighting benefits.

"Future cancer-fighting efforts are more likely to revolve around dietary adjustments than miracle pills," said Dr. Butrum. "These single-agent studies are the means to an end, not the end itself. They provide information that will allow us to enhance the anti-cancer benefits of healthy diets."

Researchers Documenting Interactivity

Laboratory tests have already taught scientists a great deal about the interaction of health-promoting substances. In tissue studies, the anti-cancer actions of natural compounds found in garlic (called allyl sulfides) are significantly enhanced in the presence of selenium and vitamin A.

Flaxseed contains two substances noted for their cancer-fighting potential: alpha-linolenic acid and lignans. In laboratory tests, these substances have independent effects on the cancer process, but together, they are better able to beneficially influence the metabolism of certain hormones.

Studies show that vitamin A exerts a protective effect against cancers, but other nutrients must first help to convert the carotenoids in food to vitamin A. In animal tests, subjects consuming diets lacking in selenium and vitamin E were less able to form vitamin A from carotenoids and showed increased cancer risk.

Dangers of the Magic Bullet

In some cases, very high doses of an isolated dietary substance may be toxic. Fatigue, diarrhea and hair loss are possible side effects of over-supplementation, but more serious problems may also occur: kidney stones, liver or nerve damage, even death. That's another reason scientists are concentrating on an approach to cancer prevention that involves the overall diet.

"There's no such thing as a natural supplement," said Dr. Butrum. "It is a contradiction in terms. The natural thing would be to get these substances in the combinations and amounts that occur in a healthy, balanced diet. There is nothing remotely natural about a supplement containing a single compound in amounts five, ten, or twenty times greater than anything found in nature."

Although AICR maintains that a predominantly plant-based diet is the best source of essential vitamins and minerals, the Institute recognizes that some individuals may need assistance. "A multivitamin supplement that helps bring nutrient levels up to recommended daily amounts will certainly do no harm," Dr. Butrum said. "We know this to be true because we have data that is strong and consistent. Decades of research have helped to establish safe, effective dosages for the various nutrients typically found in multivitamins."

No such limits have been determined for the many high-dose, single-substance supplements now flooding the market. Until research can determine the safety and efficacy of highly concentrated vitamins, minerals and herbal substances, AICR recommends that individuals check with a doctor before using these products.

For similar reasons, AICR expressed concerns about the commercial development of transgenic foods featuring unnaturally high levels of nutrients and other plant compounds. They cautioned the food industry that substances beneficial at normal dietary levels may show unknown effects when delivered in megadoses by foods that have been genetically altered. Once again, the AICR researchers called for more research.

The American Institute for Cancer Research is the only major cancer charity focusing exclusively on the link between diet and cancer. The Institute provides a wide range of consumer education programs that have helped millions of Americans learn to make dietary changes for lower cancer risk. AICR also supports innovative research in cancer prevention and treatment at universities, hospitals and research centers across the U.S. The Institute has provided over $50 million in funding for research in diet, nutrition and cancer.

For more information, or to contact American Institute for Cancer Research, see their website at: www.aicr.org