Cancer and the Role of
Environment
The role of the environment in human health is generally a subject only briefly touched upon in medical school training. It wasn't until I attended the World Breast Cancer Conference in July 1997 that I first heard discussion amongst a number of prominent scientists, physicians and other health professionals about the growing body of evidence linking environmental contamination and cancer. I became very interested in this subject since I developed breast cancer at the age of 37, with no risk factors and having breast fed three children. When I was doing my literature search on the link between cancer and pesticides, the librarian helping me stated: "I don't have to worry about exposure to pesticides. I hate gardening!" Another interested person felt she was not at risk because she did not live in farm country where all the spraying was taking place. Not many people realize that they are being exposed to minute quantities of pesticide residues, not to mention a host of other chemicals used in food preparation, every time they eat. An obvious place to start looking for the root causes of cancer is with substances that are known to cause cancer in animal models, that is carcinogens. One such class of carcinogenic substances, the organochlorines (OCs) are found all around us. They're in our drinking water, in much of our pesticide-treated food, and in many of our laundry detergents and cleaning products as well. DDT, a well-known OC, is so persistent that although its use has been banned in North America for more than 25 years, it is still found in detectable levels in the tissue and blood of people living from Florida to the high Arctic. This ban notwithstanding, OCs are still produced in North America and exported abroad, particularly to developing countries. As a consequence, imported fruits and vegetables which end up back on our dinner tables often have detectable levels of substances we know to be human carcinogens. Aside from being potentially carcinogenic, some of these chemicals also behave like a much weaker version of our body's own estrogen. Because these estrogen-like chemicals are outside the body, they are classified as xenoestrogens, "xeno" meaning "foreign" in Greek. We know that the more estrogen a woman
is exposed to during her life, the greater her risk of breast cancer.
Estrogen, essential for sexual development and reproduction, stimulates
breast cells to grow, divide and spread. Similar to "bad" and "good"
cholesterol, it's believed our body produces "bad" and "good" estrogens.
Certain xenoestrogens, like OCs, act like bad estrogens, which in turn
stimulate uncontrolled growth of breast cells. Other xenoestrogens
such as those found in plant foods like soy products, cauliflower and broccoli,
may act like good estrogens because they prevent cancer. (They are
also called phytoestrogens.)
The proposed link between chemical xenoestrogens and breast cancer came about by accident in 1991 when Tufts University researchers noticed that breast cancer cells, which need estrogen to reproduce, were growing rapidly in plastic dishes. They discovered that nonylphenol, a chemical added to plastic to prevent cracking, was leaching out of the plastic and triggering the growth of the breast cancer cells. In other words, it was acting like estrogen. The researchers then exposed other cancer cells to common pesticides, detergents and plastics, and observed the same results. The implications are disturbing, considering how common these products are in our lives. Since then, other researchers have studied the role of xenoestrogens (particularly the pesticide DDT and potentially carcinogenic chemicals known as PCBs) in the development of breast cancer. As with many such lines of inquiry, the results are not clear. Some studies have indicated a link between exposure and breast cancer, but other studies have found no connection. Some researchers say the evidence may be conflicting because these studies only give you a snapshot of the current levels of contaminants in a woman's body. This approach doesn't consider what the level of exposure might have been in the womb or during childhood, possibly the most risky times for exposure to these chemicals. In 1962, the renowned biologist, Rachel Carson, in her book Silent Spring alerted us to the poisoning of the earth with toxic chemicals. Because of her concern about pesticides, she was ridiculed by some in the chemical industry as an ignorant, hysterical woman who wanted to turn the world over to insects, and considerable resources were spent trying to discredit her. Rachel Carson died in 1964 of breast cancer. Thus far, I have discussed mainly the
link between pesticides and breast cancer because that is my special interest.
But also consider the following:
There will always be those with vested interests to argue that we do not yet have sufficient proof of a relationship between environmental contaminants and cancer and other diseases, and from a strictly scientific point of view they are correct. We can always do more research, and we will never have proof, only more evidence. How much evidence is enough? More than 50 years ago, the Surgeon General in the U.S. warned that cigarette smoking was harmful to human health. It wasn't until dozens of studies in more than 20 different countries, all showing that smoking increased the risk of lung cancer and other diseases, that governments finally took action. It took almost 25 years for warnings to appear on cigarette packages, and only in 1997 was the tobacco industry actually held legally accountable. There seems to be sufficient evidence now linking pesticides to cancer and other diseases to justify adopting a precautionary principle regarding the use of these chemicals. For too long, industry and government have been minimizing the role that environmental contaminants may play in human health. Let us learn from our experience with smoking. Let us no longer allow others to poison our planet while we remain silent. To quote Abraham Lincoln, "to sin by silence when they should protest, makes cowards out of men." Reprinted from Eco Farm and Garden Nicole Bruinsma lives with her husband and three young daughters in Chelsea, Quebec and works as a family physician in a nearby rural hospital. She is vice-president of CAPE, the Canadian Association of Physicians for the Environment, and is very active in her community on environmental issues. Related Resources:
Living Downstream: An Ecologist Looks at Cancer and the Environment, by Sandra Steingraber, Addison Wesley, 1997. The Nova Scotia Breast Cancer Action Group can be reached through their website www.bca.ns.ca See also: Prevention
is the Cure, UPdate Fall 2001
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