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, warns the American Council on Science and Health (ACSH).

An ACSH study points out that regulatory decisions are frequently based on misleading animal-test results. In 1977, for example, the FDA pronounced the artificial sweetener saccharin a carcinogen, based on laboratory tests showing that saccharin could cause cancer in rats. However scientists disputed the results.

• The rats consumed the equivalent of 1,000 cans of diet soda per day throughout their lives.

• Differences in animal and human physiology and anatomy make it difficult to predict human outcome from animal tests.

• And subsequent research has not supported the conclusion that saccharin causes cancer in humans.

Researchers say such high-dose studies violate a basic scientific principle: that the dose makes the poison. Vitamin A, for example, is necessary in small quantities for vision but at much higher doses is toxic to the liver and heart.

Yet the viability of thousands of products and the expenditure of billions of dollars -- in environmental-cleanup and pollution-abatement costs, insurance premiums, product modifications, and in legal fees -- depend on regulatory decisions made on the basis of animal testing.

The report suggests that we need a better perspective on predicting human health risk from these tests. Furthermore, 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.

Source: "Of Mice and Mandates: Animal Experiments, Human Cancer Risk, and Regulatory Policies," July 1997, American Council on Science and Health, 1995 Broadway, Second Floor, New York, NY 10023, (212) 362-7044.