Branding a substance a human carcinogen solely because cancer has occurred in laboratory animals force-fed the substance at unrealistically high doses diverts both attention and resources from far more significant threats to human health. So states a panel of experts affiliated with the American Council on Science and Health (ACSH).
Says ACSH President Dr. Elizabeth Whelan: "The problem is that cancer findings from animal experiments are too often applied uncritically to human health. Such extrapolation becomes fuel for unfounded health scares that distract consumers, politicians, and even some scientists from proven cancer causes." In a newly released booklet, Of Mice and Mandates: Animal Experiments, Human Cancer Risk, and Regulatory Policies, ACSH examines the history, uses, and limitations of animal testing in determining human cancer risk.
According to Simona Kwon, ACSH's Coordinator of Epidemiology Projects, "For too long, animal experiments employing very high doses of a single agent amounts that are not realistic approximations of human exposure have formed the basis for decisions vital to our health and standard of living." Adds Dr. Whelan: "The high dose itself may cause cancer by adversely affecting cellular metabolism."
Regulatory decisions are frequently based on misleading animal-test results. In 1977, for example, the FDA pronounced the artificial sweetener saccharin a carcinogen. The evidence? Laboratory tests showing that saccharin could cause cancer in rats that consumed the equivalent of 1,000 cans of diet soda per day throughout their lives. Subsequent research has not supported the conclusion that saccharin causes cancer in humans. Differences in animal and human physiology and anatomy make it difficult to predict human outcome from animal tests.
The viability of thousands of products and the expenditure of billions of dollars in environmental-cleanup and pollution-abatement costs, in insurance premiums, in product modifications, and in legal fees depend on regulatory decisions made on the basis of animal testing. Clearly, we need a better perspective on predicting human health risk from these tests. If we mistakenly persist in classifying as "probable human carcinogens" chemicals that pose no threat of human cancer, we end up incurring new risks by the very act of rejecting things that could make our lives healthier and more enjoyable.
As Dr. Whelan states, "One positive animal test is not sufficient to identify true human health risks or lead to appropriate exposure guidelines. At the very least, we need to know that a suspect compound will yield positive results in more than just one species. If a substance consistently causes cancer in mice, rats, and birds as does aflatoxin, a 'natural' toxin produced by some molds on grains it is prudent to limit human exposure to such a compound."
"But," she adds, "trying to purge from our environment every last trace of any chemical that at high doses causes cancer in laboratory animals will jeopardize our standard of living, our economic growth, and the state of our public health. We must be guided by common sense and set acceptable tolerance exposures that pose no threat to human health."