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World Cancer Day reminds us to look at complex causes of disease

Feb 01, 2018

As a guest blogger, Susan Davidson describes how science is evolving in understanding the links between environmental toxins and cancer and birth defects. She serves as Secretary on Midwest Environmental Advocates Board of Directors.

Susan is a physician in Maternal Fetal Medicine at Dean/SSM Health, a specialization which focuses on delivery care to women with high risk pregnancies. Since she began practicing medicine in 1986, Susan's concern over increased birth defects in children of rural women led to her strong interest in the influence of environmental factors on human health. She currently serves on the Wisconsin Birth Defects Surveillance Committee, the Wisconsin Maternal Mortality Committee, the Dane County Fetal and Infant Mortality committee, the Legislative and Advocacy Committee of the Wisconsin March of Dimes and the steering committee of the Wisconsin Environmental Health Network.

I am a physician specializing in Maternal Fetal Medicine and have focused on safely ushering babies into this world when pregnancies are faced with a variety of challenges. 

My journey as a physician in Maternal Fetal Medicine led me to understand that to promote health and prevent disease and birth defects, we must address the underlying causes of disease including the influence of natural, created and social environments. I became curious about the effect of the environment on pregnancy when I noticed certain unusual categories of birth defects in my practice, kinds of defects that we didn’t see frequently during my training in New York. I learned that, indeed, the incidence of certain birth defects is rising and that it is partly attributed to environmental exposures. 

I became passionate about the topic of the environment and health when I learned that exposures contribute to the increase in frequency of a variety of diseases ranging from infertility to obesity and diabetes. With World Cancer Day on February 4th, I’m reminded of another reason to be concerned about environmental threats to our health. 

Cancer is a group of about 200 diseases in which abnormal cells divide and can invade other tissues. The causes of cancer are complex and involve an interaction of genetic predisposition, lifestyle factors such as smoking and diet and the environment. About 30% of cancers are due to smoking. Another 30% are attributable to alcohol use, physical inactivity and dietary choices. In the medical literature, about 6% of cancers are attributed to environmental exposures, most of them occupational. 

However a recent governmental task force points out that what we don’t know can still hurt us and “the true burden of environmentally induced cancers has been grossly underestimated.” Others say that we will never be able to pinpoint the exact contribution of the environment to cancer because all exposures interact with other exposures in addition to our lifestyle and genetic predisposition.

So what do we know about environmental exposures that lead to cancer? 

The list of known carcinogens is not likely to shrink and is very likely to lengthen in the future.  The federal government has listed over 30 chemicals that are known carcinogens with an additional 60 that are likely to be proven carcinogens. Common exposures such as BPA, which has been linked to breast and uterine cancer, and glyphosate (Roundup), which has been rated as “probably carcinogenic to humans” by the United Nation’s International Agency for Research on Cancer, have not been included. Many additional chemicals are in the process of being evaluated or have not been adequately studied. 

With expanded research, “safe” levels of exposures tend to decrease. For example in 1960, a blood lead level of 60 ppm was considered safe. This level dropped to 10 in 1991 and then to 5 in 2012. The CDC recently stated that there is no known safe level of lead. We can expect a similar pattern to emerge with other environmental exposures.

Science will be helpful but will not give us all the answers. Scientific approaches are becoming more technically sophisticated and have longer horizons. The effects of early exposures might not be manifest until much later in life. We now know, for example, early breast buds are developed in utero and are sensitive to maternal exposures. Some breast cancer appears to have its origin in fetal life. Studying these long-term effects is very challenging because, as we know, much life happens between the womb and adulthood.

Ultimately as a society we will have to decide what level of risk we wish to take with people’s health. Strict scientific standards may be appropriate for judging scientific publications but the precautionary principle suggests that less strict standards for proof are more protective of the public good. The European Union tends to be much more cautious than the United States. For example, the pesticide atrazine is commonly used in the United States but is banned in Europe.

On a personal note, I was drawn to Midwest Environmental Advocates because their commitment to our rights to clean water, air and land is also a commitment to our health and, even more importantly, the health of our children and future generations.  I have been serving on the MEA board since 2017.

For further information on issues focusing on the environment and health, please attend the annual conference sponsored by the Wisconsin Environmental Health Network, a sister organization to Midwest Environmental Advocates. The program on March 2 is fascinating and features a talk on the environment and breast cancer. To view the program and register visit: wehnonline.org/mtc-2018

For information on cancer, toxins and human health, the National Institute for Environmental Sciences and Physicians for Social Responsibility have more online.

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