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The major avoidable causes of cancer are: (1)
smoking, which accounts for 27% of cancer deaths in Canada and
80% to 90% of deaths from lung cancer; (2) dietary imbalances
(e.g., lack of sufficient amounts of dietary fruits and
vegetables), which account for about another third; (3) chronic
infections, mostly in developing countries; and (4) hormonal
factors, which are influenced primarily by life-style.
There is no cancer epidemic except for lung cancer due to
smoking. (Cancer is actually many diseases, and the causes differ
for cancers at different target sites.) Since 1971, overall
cancer mortality rates in Canada (excluding lung cancer) have
declined 17% in women and 5% in men. Regulatory policy that
focuses on traces of synthetic chemicals is based on
misconceptions about animal cancer tests. Current research
indicates that it is not rare for substances to cause cancer in
laboratory rodents in the standard high-dose experiments. Half of
all chemicals tested, whether occurring naturally or produced
synthetically, are "carcinogens"; there are high-dose effects in
rodent cancer tests that are not relevant to low-dose human
exposures and which may contribute to the high proportion of
chemicals that test positive.
The focus of regulatory policy is on synthetic chemicals, but
99.9% of the chemicals humans ingest are natural. For example,
more than 1000 naturally occurring chemicals have been described
in coffee: 30 have been tested and 21 have been found to be
carcinogenic in rodents in high-dose tests. Plants in the human
diet contain thousands of natural "pesticides" produced by plants
to protect themselves from insects and other predators: 72 have
been tested and 38 have been found to give cancer to rodents.
Thus, exposure to synthetic rodent carcinogens is small compared
to the natural background of rodent carcinogens. High-dose rodent
cancer tests need to be re-evaluated by viewing results from this
perspective.
There is no convincing evidence that synthetic chemical
pollutants are important as a cause of human cancer. Regulations
targeted to eliminate low levels of synthetic chemicals are
enormously expensive: the United States Environmental Protection
Agency (EPA) has estimated that environmental regulations cost
$140 billion per year in the United States. Others have estimated
that the median toxic control program costs 146 times more per
hypothetical life-year saved than the median medical
intervention. Attempting to reduce low hypothetical risks has
other costs as well: if reducing synthetic pesticides makes
fruits and vegetables more expensive, thereby decreasing
consumption, then the cancer rate will likely increase. The
prevention of cancer will come from knowledge obtained from
biomedical research, education of the public, and life-style
changes made by individuals. A re-examination of priorities in
cancer prevention, both public and private, seems called for.
In this study, we highlight nine misconceptions about pollution,
pesticides, and the causes of cancer. We briefly present the
scientific evidence that undermines each misconception. The nine
misconceptions are listed in Contents (p. v-vi) and an extensive
bibliography is provided in References and further reading (p.
99). Phrases in the text typeset like this, carcinogenic potency,
are defined in the Glossary (p. 91).
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