What Causes Cancer and What Doesn't

Oct 19, 2005

The Bottom Line It is a common misconception that synthetic chemicals in the environment cause cancer. What about your organic celery sticks?

In a short scholarly book published in 2002 by the Fraser Institute and entitled "Misconceptions about the Causes of Cancer" (not in the epinions database), Lois Gold, Thomas Sloane, Neela Manley and world-famous biochemist Bruce Ames set out to burst many of the popular misconceptions about one of the most dreaded and misunderstood diseases: cancer. The book is of high scientific quality and the claims made by the four scientists are either evident truths or reasonable conclusions. It contains as many as 42 pages of literature references.

I think it is important to share some of their controversial claims, because the general public is bombarded by incomplete, biased or simply distorted accounts of the cause of cancer. Armed with tons of data, Ames and company go on to offer the following conclusions:

There is no cancer epidemic in the Western World
When properly calculated and corrected for confounding factors, cancer death rates have slightly declined in the US and Canada over the last 50 years. Therefore, there is no need for a theory on a "cancer explosion".

Synthetic chemicals in the environment are not a significant cause of human cancers
The main cause of cancer is aging. Cancer is dictated by our own DNA replication apparatus. It can be triggered by a variety of factors which lead to DNA damage. It can be slowed down by a diet rich in vitamins (antioxidants, especially), control of infections (viral and bacterial) and avoidance of certain lifestyles (such as smoking or excess body weight) which have been clearly linked with cancer.
It is unlikely and undocumented throughout the literature that pesticides, herbicides, additives and other chemicals found in small amounts in the environment are a significant cause of cancer. Strong correlations have never been established. In addition, chemically this is extremely illogical. Most of the chemicals humans ingest (>99.99%) are of natural origins (dietary). Many of these chemicals are rat carcinogens. There is nothing specific in artificial chemicals which makes them more dangerous than natural ones. Humans have evolved non-specific detoxification mechanisms (metabolic transformations) which are able to handle basically any chemical they may come in contact with.

Natural chemicals are more dangerous than synthetic ones
The world is full of poisons. Plants defend themselves by trying to poison potential predators, and do so by producing a stunning variety of substances called alkaloids, many of which are either toxic or carcinogenic in rats. Our diet includes 5,000-10,000 of such natural pesticides, which is equivalent to 1.5 g per day for each American. This is 10,000 more, by weight, than our intake of synthetic pesticides. Yet natural pesticides, although present in every edible plant from lettuce to broccoli, have only rarely been tested as carcinogens. Of those which have been tested, 50% have displayed carcinogenic potential at some dose. Cooked food is even more toxic. We ingest about 2g per day of burnt natural substances, which contain even more carcinogenic compounds (indeed barbecued meats can contain substantial amounts of benzopyrene, one of the most potent carcinogens known). All this does not show that eating broccoli or hamburgers is a significant cause of cancer. It simply confirms intuitively what statistics show: synthetic pesticides are not a cause of cancer.

The toxicology of synthetic and natural chemicals is the same
This is self-evident to all those who have studied chemistry or biology. Our coexistence with edible plants does not per se ensure that they are not carcinogenic. There is no reason why artificial chemicals should be treated as potentially more hazardous than those we ingest every day through the diet. "Natural selection works far too slowly for humans to have evolved specific resistance to food toxins". Indeed, the organic approach to pest control often leads to strains that overproduce natural toxins, and are therefore even more toxic to humans. Cases are cited where organic vegetables like celery caused rashes in humans because of an extremely large content (6,200 ppb) of a natural toxin (a carcinogen): psoralene. In contrast, crops which were pesticide-protected did not need so much natural defense and contained only 800 ppb of the poison. Ames and co. argue, armed with data like these, that organic vegetables may well be more harmful than vegetables grown under the protection of synthetic pesticides.

Cancer risks for humans cannot be adequately predicted by rodent data
When rodents are given huge doses of synthetic chemicals, they are able to develop cancer through a variety of mechanisms, including cell death and increased tissue repair. Extrapolation of these data to lower levels of exposure in other species is especially problematic. For example, of the 1,000 chemicals coffee contains, 31 have been identified and tested in rodents, and 20 have been found to be carcinogenic. Yet studies with heavy coffee drinkers have not evidenced higher cancer rates. Indeed, it is the dose and not the compound that causes cancer. The same substance can protect us from cancer at a certain dose, and cause cancer at a higher dose!

Herbal supplements have higher carcinogenic potential than prescription drugs
Prescription drugs are tested for carcinogenicity and are, in all cases, free from carcinogenic potential at the prescribed doses. In contrast, no such testing is necessary for herbal remedies, as the FDA 1994 dietary act does not require non-therapeutic herbal treatments to show safety. Many people believe that nature is a benevolent entity and provides us with a “natural cure” to our ailments. This is a religious view that is contradicted by scientific evidence. The most dangerous poisons are all produced by nature. Herbs contain small amount of toxins, many of which have been isolated and shown to be carcinogenic. Ames and co. warn that “there is an imbalance in the testing of synthetic chemicals compared to natural chemicals.” Indeed, if the same HERP ratings (a carcinogenicity estimation index) used to control synthetic chemicals were applied to fruits, vegetables and herbs, over 90% of them would be banned.
This discrepancy in dealing with natural vs. synthetic chemicals, we are reminded once again, is without merit scientifically. In the 15 pages that follow, an interesting table compares cancer risks from DDT ingestion with consumption of foods like tomatoes and apples. The latter have higher HERP values!

There is no doubt that the battle to curb synthetic chemicals in our environment is being fought with much irrationality and a religious fervor which is based on misinformation. Cancer is a highly misunderstood and complex class of diseases. There is no evidence that an appreciable contribution to cancer is caused by low levels of pesticides and other chemicals introduced by industry into the environment. Ames and company remind us that natural chemicals, i.e. those in plants and animals, are not different in any fundamental way from the synthetic ones. Like them, they have been selected to kill and they are often toxic. The fact that we can ingest them with our food without dying does not prove that they are safe. Any intelligent policy aimed at curbing cancer must take into account these simple facts. The public must be educated urgently, because the general understanding of biology and toxicology among Americans is pitifully low. Personal decisions are being routinely made with no basic understanding of the issues.

Finally, Ames is a scientist of international stature and cannot be suspected of being on the payroll of the chemical industry. His data have been collected over 30 years with painstaking accuracy and analyzed with criticism. His general conclusions are strongly supported and should be given our utmost attention.

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