UC Berkeley press release

NEWS RELEASE, 11/01/97

Misconceptions about the causes of cancer lead to skewed priorities and wasted money, UC Berkeley researchers say

by Robert Sanders


BERKELEY -- Despite a lack of convincing evidence that pollution is an important cause of human cancer, this misconception drives government policy today and results in billions of dollars spent to clean up minuscule amounts of synthetic chemicals, say two UC Berkeley researchers.

This is only one of many misconceptions, they say, that serve to divert money from the most important causes of cancer: smoking, poor diet, our own hormones and chronic infections.

"One of the big misconceptions is that artificial chemicals such as pesticides have a lot to do with human cancer, but that's just not true," says Bruce N. Ames, professor of biochemistry and molecular biology at the University of California at Berkeley and co-author of a new review of what is known about environmental pollution and cancer. "Nevertheless, it's conventional wisdom and society spends billions on this each year."

"We consume more carcinogens in one cup of coffee than we get from the pesticide residues on all the fruits and vegetables we eat in a year," he adds.

Though there may be many excellent reasons for cleaning up pollution of our air, water and soil, the researchers say, prevention of cancer is not one of them.

The message is the same one Ames and co-author Lois Swirsky Gold have hammered for more than 15 years -- that trace chemicals in the environment, such as pesticide residues on food, are not significant causes of human cancer, while the main causes are lifestyle factors.

"The problem is that lifestyle changes are tough," says Gold, director of the Carcinogenic Potency Project at UC Berkeley's National Institute for Environmental Health Sciences Center and a senior scientist in the cell and molecular biology division at Lawrence Berkeley National Laboratory.

"But by targeting pesticide residues as a major problem, we risk making fruits and vegetables more expensive and indirectly increasing cancer risks, especially among the poor."

The review by Ames and Gold appears in the November issue of The FASEB Journal, the official publication of the Federation of American Societies for Experimental Biology.

The new paper updates a major study of cancer hazards the team published in the journal Science in 1992. The current study provides even stronger evidence, much of it from a one-of-a-kind database created by Gold containing the results of all chronic, long-term animal cancer tests. Called the Carcinogenic Potency Database, it summarizes decades of animal studies, totaling 5,000 experiments on more than 1,300 chemicals. Gold has made it available on the web at http://potency.berkeley.edu/cpdb.html.

One of the clearest conclusions from the database, Gold says, is that our perception of what constitutes a cancer hazard has been skewed by the kinds of chemicals that are tested. Whereas 99.9 percent of all the chemicals we ingest are natural, 78 percent of the chemicals tested are synthetic. So when more than half of all synthetic chemicals are found to cause cancer in rodents, it's not surprising that people link cancer with synthetic chemicals.

But of the natural chemicals in our diet that have been tested in animals, half also cause cancer, Gold says.

"Our assumptions have been wrong," Gold says. "We need to recognize that there are far more carcinogens in the natural world than in the synthetic world, and go after the important things, such as lifestyle change."

The misconception that synthetic chemicals are an important cause of cancer is one of nine misconceptions the two researchers discuss in their paper, which grew out of testimony Ames presented to the U.S. Senate last year.

"We need to reexamine our priorities in cancer prevention," Ames urges. "The government should spend the taxpayers' money more wisely on the major causes of cancer, so as to save the most lives for the dollar."

Among the other misconceptions:

Misconception: Cancer rates are soaring. In fact, the researchers say, if lung cancer due to smoking is excluded, overall cancer deaths in the U.S. have declined 16 percent since 1950.

Misconception: Reducing pesticide residues is an effective way to prevent diet-related cancer. Because fruits and vegetables are of major importance in reducing cancer, the unintended effect of requiring expensive efforts to reduce the amount of pesticides remaining on fruits and vegetables will be to increase their cost. This will lead to an increase in cancer among low income people who no longer will be able to afford to eat them.

Misconception: Human exposures to carcinogens and other potential hazards are primarily due to synthetic chemicals. Americans actually eat about 10,000 times more natural pesticides from fruits and vegetables than synthetic pesticide residues on food. Natural pesticides are chemicals that plants produce to defend themselves against fungi, insects, and other predators. And half of all natural pesticides tested in rodents turn out to be rodent carcinogens. In addition, we consume many other carcinogens in foods because of the chemicals produced in cooking. In a single cup of roasted coffee, for example, the natural chemicals known to be rodent carcinogens are about equal in weight to an entire year's work of synthetic pesticide residues.

"This does not mean that coffee or natural pesticides are dangerous, but rather that assumptions about high-dose animal cancer tests for assessing human risk at low doses need reexamination," they write.

Misconception: Cancer risks to humans can be assessed by standard high-dose animal cancer tests. In cancer tests, animals are given very high, nearly toxic doses. The effect on humans at lower doses is extrapolated from these results, as if the relationship were a straight line from high dose to low dose. However, the fact that half of all chemicals tested, whether natural or synthetic, turn out to cause cancer in rodents implies that this is an artifact of using high doses. High doses of any chemical can chronically kill cells and wound tissue, a risk factor for cancer .

"Our conclusion is that the scientific evidence shows that there are high-dose effects," Ames says. "But even though government regulatory agencies recognize this, they still decide which synthetic chemicals to regulate based on linear extrapolation of high dose cancer tests in animals."

Misconception: Synthetic chemicals pose greater carcinogenic hazards than natural chemicals. Naturally occurring carcinogens represent an enormous background compared to the low-dose exposures to residues of synthetic chemicals such as pesticides, the researchers conclude. These results call for a reevaluation of whether animal cancer tests are really useful guides for protecting the public against minor hypothetical risks.

Misconception: The toxicology of synthetic chemicals is different from that of natural chemicals. No evidence exists for this, but the assumption could lead to unfortunate tradeoffs between natural and synthetic pesticides. Recently, for example, when a new variety of highly insect-resistant celery was introduced on a farm, the workers handling the celery developed rashes when they were exposed to sunlight. The pest-resistant celery turned out to contain almost eight times more natural pesticide in the form of psoralens -- chemicals known to cause cancer and genetic mutations -- than common celery.

Misconception: Pesticides and other synthetic chemicals are disrupting human hormones. Claims that synthetic chemicals with hormonal activity contribute to cancer and reduced sperm count ignore the fact that natural chemicals have hormone-like activity millions of times greater than do traces of synthetic chemicals. Rather, lifestyle -- lack of exercise, obesity, alcohol use and reproductive history -- are known to lead to marked changes in hormone levels in the body.

Misconception: Regulating low, hypothetical risks advances public health. Society -- primarily the private sector -- will spend an estimated $140 billion to comply with environmental regulations this year, according to projections by the Environmental Protection Agency. Much of this is aimed at reducing low-level human exposure to chemicals solely because they are rodent carcinogens, despite the fact that this rationale is flawed. Our improved ability to detect even minuscule concentrations of chemicals makes regulation even more expensive.

"We put up an enormous amount to regulate this and that, and get very little health benefit for the money," Ames says. "These efforts distract from the major task of improving public health through increasing biomedical research, education of the public and lifestyle changes made by individuals."

The research by Ames and Gold is supported by a National Cancer Institute Outstanding Investigator Grant, funds from the Office of Energy Research of the U.S. Department of Energy, and the National Institute of Environmental Health Sciences of the National Institutes of Health.

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