Posts Tagged ‘endocrine disruptors’
Science-Based Medicine, a physicians’ group blog takes to task a recent documentary by the Canadian Broadcasting Corporation, “The Disappearing Male”, which mixes endocrine disruption science with overheated rhetoric to raise the question of the decline of the human species.
The post represents informed advocacy, and can scarcely be considered a full characterization of potential endocrine disruptor risks. While I have some minor disagreements with a few of its sources, overall it needs to be acknowledged as a welcome counterpoint in the endocrine disruption debate.
Science-Based Medicine: “The Disappearing Male – a Pinch of Science, a Pound of Speculation”.
[Note: this a series of posts stimulated by this recently-published research on breast cancer risks from multiple environmental contaminants. A previous post is here.]
I have been aware of initiatives to address endocrine disrupting chemicals, early-life exposure to environmental contaminants, and cumulative risk assessment but over the past few years hadn’t paid that much attention to them. While all of these topics had public health importance, and were beginning to turn into risk assessment guidance, regulatory agencies just haven’t been requiring them to be used for making decisions about the kinds of problems affecting my clients. So, they were more of an intellectual curiosity.
That might be changing. In 2005, EPA published guidelines for assessing susceptibility from early life exposure to carcinogens. In 2008, EPA updated the screening levels used for evaluating contaminant data at Superfund sites and incorporated the early life exposure guidelines for selected carcinogenic chemicals. Guidance on how to conduct cumulative risk assessments is steadily becoming more specific, and all of this represents a sea-change in how to perform risk assessments which the National Academy of Sciences says is overdue.
A recent review article argues there is substantial evidence that hormonal perturbations early in life (either in utero or during early development) are associated with increased disease susceptibility later in life, with two examples being prostate and breast cancer. The Endocrine Society has recently issued a scientific policy statement (news items here and here; link to the report here) identifying endocrine disruptors as a significant public health concern. The thrust of these stories is that professional societies are becoming involved not in just generating the science but in encouraging that it be used in policy making.
BPA, which was mentioned in the previous post, gets its own chapter in the Endocrine Society’s report. Low-dose exposure in rat fetuses to has resulted in alterations in mammary tissue. Higher dose prenatal exposures (i.e. where the pregnant females are dosed with BPA) increase the numbers of precancerous lesions in next-generation rats later in life. BPA increased mammary tumor incidence in animals when administered along with rodent carcinogens such as nitrosomethylurea and dimethylbenzanthracene. The Endocrine Society’s summary statement is:
These results indicate that perinatal exposure to environmentally relevant doses of BPA results in persistent alterations in mammary gland morphogenesis, development of precancerous lesions, and carcinoma in situ.
Or, exposure to levels of BPA, which you might normally encounter through your daily routine, might, if you’re pregnant, predispose your female child to an increased breast cancer risk. The Endocrine Society speculates that the increased incidence of breast cancer observed over the last 50 years might have been caused in part by exposure of women to endocrine-mimicking chemicals.
Of course, it’s risky to let yourself get tunnel-vision and focus on only one answer. In 2002, reports that post-menopausal hormone therapy posed an increased breast cancer risk resulted in a rapid decline in this kind of hormone use in women. The decline in hormone use is suspected to be a contributor to the subsequent decline in breast cancer rates. Would reducing BPA exposure in a systematic manner, also result in a decline in breast cancer rates? It would be hard to say – an epidemiological investigation of post-menopausal hormone therapy is a good deal simpler than investigating BPA; 93% of Americans have detectable levels of BPA in their bodies – where do you find a control population?
Not done yet. . . .
Bisphenol-a, used to manufacture polycarbonate including plastics for food and beverage containers, has been found to leach from those containers, is consumed by us and can be detected at trace levels in nearly everyone’s blood and urine. Bisphenol-a is hormonally active (otherwise known as an endocrine disruptor), and produces reproductive and developmental abnormalities in laboratory animals including changes in mammary glands. The kinds of changes observed in mammary tissue leads some to be concerned that bisphenol-a might pose some level of risk for breast cancer.
By itself, maybe the breast cancer risk from bisphenol-a (or BPA) by itself isn’t something a woman ordinarily needs to be concerned about. There isn’t any certainty about it, and the effects observed in lab animals are pretty subtle. But we’re not exposed to BPA by itself, but as mixtures of contaminants. Other chemicals that we’re commonly exposed to that are possible human carcinogens are polycyclic aromatic hydrocarbons (PAHs). PAHs are found in tobacco smoke, air pollutants, motor vehicle exhaust, particularly diesel, and some fried or smoked foods. One PAH, dimethylbenzanthracene (DMBA) reliably causes mammary cancer in a selected strain of rat, so that DMBA-rat system is used as an animal model for breast cancer research.
A study published a few months ago in Environmental Health Perspectives explored the hypothesis that exposure to BPA early in life would produce changes in mammary tissue, creating a predisposition for breast cancer. This study investigated the interaction between BPA and breast cancer risks by exposing newborn rats to BPA through lactation, then giving the young female rats oral doses of DMBA.
Those tending to be skeptical about environmental contaminant-disease trend relationships might be inclined to note that breast cancer incidence and mortality rates have declined over the past several years. When you browse the SEER statistics directly (breast, Figure 4.2), mortality hovers a little over 50 per 100,000, while incidence hovers around 300-350 per 100,000. While a decreasing trend is good news, a worthwhile question then is how many cases are too many? Note: yes, I know zero would be nice, but let’s stay in the real world for now. . . . The CDC reports that in 2005, about 186,000 women were diagnosed with breast cancer and 41,000 died from it. Aside from the financial and human costs, there is the issue that a substantial fraction of those cases may still be avoidable.
To be continued. . . .