Causes of Cancer

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The authors of the short volume Misconceptions about the Causes of Cancer (UC Berkeley scientists Lois Swirsky Gold, Thomas H. Slone, Neela B. Manley, and Bruce N. Ames) deserve a great deal of credit for having the courage to write a somewhat dry book. But let me explain.

Cancer-causation is a heated topic, especially with activists turning up the rhetoric in recent months, claiming that our entire environment is not only saturated with deadly amounts of synthetic chemicals but that those chemicals act in concert to cause everything from leukemia to brain tumors. It's tempting to respond to the activists' heated rhetoric in kind, but nothing persuades at least, persuades those who are willing to listen as effectively as the cold, hard facts, painstakingly explained and footnoted.

What's exciting about Misconceptions is that the authors have the courage to tell the sometimes boring truth: that virtually all preventable cancer is accounted for not by mysterious environmental chemicals but by smoking, dietary imbalances (such as not eating fruits and vegetables), chronic infections (mostly in developing countries), hormonal factors, and sedentary lifestyles.

Booooring! With reality TV shows, battlefront footage from Iraq, antiwar protesters lying in the streets and blocking traffic (as I write this from New York City), and the occasional kidnapped child competing for the public's attention, who can get excited over an anti-cancer message as mundane as "eat your fruits and vegetables"? Alarmist news shows have to get our attention by saying the food in our refrigerators will kill us, that children's toys are made of toxic plastic, and that evil corporations are experimenting on our bodies.

Listening to the Science

In reality, as Misconceptions calmly and cautiously details (without descending into the media muck as I did in the previous paragraph), cancer rates are not increasing (once the advancing age of the population and the mid-century increase in smoking are taken into account), synthetic chemicals such as pesticides have not been shown to contribute to human cancer, and what may be co-author Bruce Ames' most important insight people consume several thousand times more carcinogens from nature itself (since, for instance, plants naturally produce pesticide) than from man-made sources. And nature's chemicals (it's almost redundant to say that, since nature is mostly made of chemicals) are no less carcinogenic than man's, contrary to what the organic food crowd might tell you. About half the naturally occurring chemicals to which we are exposed have been shown to cause cancer in lab rodents if given to them in astoundingly high doses, and the same is true of about half of synthetic chemicals.

But then, as Misconceptions explains, it's highly unlikely that rodent tumors at high levels of exposure are such an accurate predictor of human illness at extremely low exposures. "High doses can cause chronic wounding of tissues, cell death, and consequent chronic cell division of neighboring cells. This is a risk factor for cancer...because each time a cell divides, the probability increases that a mutation will occur...At the low levels to which humans are usually exposed, such increased cell division does not occur." Indeed, some of the chemicals that cause cancer in mice at high doses do not even cause cancer in rats, let alone humans, so rodent tests are far from the final word.

Misconceptions walks us through the major chemical sources of concern, the standards used to judge carcinogenicity, and whenever possible the precise reasons that regulators have restricted use of the chemical or reversed the restriction, as in the case of saccharin. Saccharin turned out to cause cancer in lab rats only because it fostered the formation of irritating crystals in the rats' urine, in a way that does not happen in humans. We are even treated to a lengthy table of the most potent known rodent carcinogens, with numbers on the level of normal human exposure vs. minimally-carcinogenic exposure levels for the lab rodents.

This one convenient volume tells the history of how some of the most notorious chemicals the ones invoked by the anti-chemical activists came to be thought of as dangerous, sometimes due to careless extrapolations from unusual cases in which humans were exposed to levels like those the lab rats face: high-level, chronic, occupational exposure to fumes and particles the likes of which no average citizen and no one in a modern work environment would face.

The track record of chemicals much like the real causes of cancer turns out to be far less mysterious and sinister than one might have assumed on the basis of political rhetoric and scary news stories. We're not entirely in the dark about what chemicals do nor about what our bodies do. Or at least we needn't be. We have this handy little book, after all.

Misconceptions about the Causes of Cancer can be read online or ordered from the Fraser Institute at:


April 1, 2003

Dear ACSH:

You are correct when you say that many (if not most) of the causes of cancer are preventable through better nutrition and lifestyle habits.

Yet, when you consider the huge volume of chemicals dumped upon earth and water in the name of "agriculture," it's no wonder people have cancer! And then our "mainstream" medical people give us their "ultimate" cure for that cancer: chemotherapy, with still more chemicals! Unbelievable! Especially when 80% of surveyed doctors would not use this barbaric procedure on themselves.

If you want to encourage people to take better care of themselves by eating better foods you should stop criticizing organic foods. Doesn't it make sense that people who are passionate about the food they produce would produce healthier food that is also better for the earth (through crop rotation, etc.)? Studies also show that consumers overwhelmingly reject genetically-modified foods. No wonder the industry refuses to label it as such.

Americans will become healthy when the veil of official ignorance is lifted from their eyes.