Canary in the Coal Mine: Breasts, Lactation, and the Environment
“Breasts: A Natural and Unnatural History” by Florence Williams was released this week by Norton Publishing. I am generally a sucker for non-fiction books about science and medicine, and obviously mammary glands are my stock and trade, so I went into the book with high expectations and no little amount of fear. As Aimee Ploudre cautioned during grad school “Expectations are disappointment under construction.”
Well no caution was necessary; this book is superb.
Early in the introduction, once Williams reminds us that breasts “turn babies and grown men into lunkheads,” she goes directly to the heart of the matter – “Its remarkable how little we know about their basic biology. We know some things: they appear out of nowhere at puberty, they get bigger in pregnancy, they’re capable of producing prodigious amounts of milk, and sometimes they get sick.” And thus begins a detailed and engaging journey through their evolutionary origins, their role in cultural constructs, and their status as "canary in the coal mine" for environmental toxins.
Williams gets a standing ovation* just for stating that although all mammals have mammary glands, “only humans have breasts the way we do, with our pleasant orbs sprouting out of puberty and sticking around regardless of our reproductive status.” It kills me every time I review a manuscript about non-human primates in which the authors uses the term “breasts.” Even better, she effectively explores the two perspectives in the scientific community about the evolutionary process that favored the human breasts: sexual selection or natural selection.
This measured, balanced approach to understanding breasts is a key feature of the book, weaving together alternative hypotheses, strengths and weaknesses of empirical data, theoretical foundations, and implications for women, babies, and men.
Yes men. In one of the more poignant chapters of the book, Williams discusses the breast cancer cluster among Marine servicemen and sons of marines stationed aboard Camp Lejeune in North Carolina. A number of environmental toxins such as the industrial chlorinated solvents trichloroethylene (TCE) and perchloroethylene (PCE) permeated some of the water supply exposing service-persons and their families. The causes of breast cancer in women, other than radiation, are very difficult to determine. How old a woman was when she got her first period, reproductive history, and underlying genetic predispositions interact in complex ways to affect a woman’s risk of developing breast cancer. Therefore identifying how environmental toxins contribute to breast cancer in women is confounded by contributing factors deriving from motherhood. For this reason, Marine servicemen provide some of the most compelling evidence that environmental exposure to toxins increases breast cancer risk.
He was diagnosed with breast cancer in 1998.
And many of those toxins *heart* your body fat, especially in the mammary fat pad full of those lovely estrogen receptors toxins can bind to. Toxins make their way to your breasts, set up shop, and hang out for decades. On the plus side, when you lactate you can mobilize those toxins into breast-milk and shed them from your body. But the really crappy downside is that toxins are transferred directly into your developing infant’s body. Ruh roh.
Moving up the food chain, toxin concentrations increase in biomaterial. Mammalian babies exist one trophic level above their adult parents because the complex biofluid that is milk is composed, in part, of maternal tissues. Babies basically eat their moms. Populations that consume foods from high on the food chain, or lots of food packaged in plastics, have some of the highest levels of toxins in their milk. Human milk, were it to be sold in a grocery store, would “exceed the federal safety levels for some chemicals in food.”
For these reasons, Williams posits “Breasts are our sentinel organ. They offer us a window into our rapidly transforming world and the excuse to steward it better.” Personally, I would have gone a couple steps further and substituted ‘mandate’ for ‘excuse’ in that sentence. A lot of our food is grown, fed, or packaged in persistent organic pollutants, the consequences of which are barely understood. Research studies are needed to compel legislation to make our food safer.
In fact, just this week, a paper came out in PNAS that reports how exposure to environmental toxins affects mammary gland development in the rhesus monkey! Pregnant rhesus monkeys were fed bisphenol A (BPA) during the third trimester to attain levels comparable to those found among women living in the US. At birth, the “density of mammary buds was significantly increased in BPA-exposed monkeys, and the overall development of their mammary gland was more advanced compared with unexposed monkeys.” These changes in mammary development are likely to lead to changes in milk synthesis and potentially increases in breast cancer risk, as has been previously found in rodent models. Dr. Patricia Hunt, a co-author on this study, has done pioneering work on understanding how BPA is a hormonal disrupter, and is featured prominently in “Breasts.”
To momentarily digress, primate models in this type of research are going to be critically important, and not just to replicate and validate research in rodent models. Environmental toxins are likely to have unique consequences in the developing human and non-human primate that may not be able to be detected in a mouse. Monkeys, like humans, have long life spans so they have a longer time to accumulate and retain environmental toxins than do rodents. Most humans and non-human primates have very expanded neurodevelopment during infancy and environmental toxins impair cognition and possibly psychological development. Primates usually produce a single infant at a time so toxins transferred from mothers via the placenta and breast-milk are concentrated in one infant rather than distributed among a litter of pups. Lastly humans, not even considering the modern obesity epidemic, have more body fat that stores toxins than do rodents so our toxic "load" is potentially higher per unit body mass.
Many other topics are covered in “Breasts” – the Texan advent of breast augmentation, the nuts and bolts of milk synthesis, and how mother’s milk promotes a healthy intestinal microbiota long before we get the memo from Jamie Lee Curtis about Activia. And an important take home message is that despite the toxins in breast-milk, other beneficial factors in breast milk compensate. This book covered so much I didn’t know about breasts, even after years of conducting milk research, reading lactation articles, and talking with awesome colleagues- some of whom are featured in this book! (Aside, Williams does a phenomenal job of capturing the joie de science of both Olav Oftedal and Bruce German).
Florence Williams has delivered a Breast “Silent Spring” if you will, one that will be of substantial value and information to scientists and policy-makers as well as our mothers and daughters… and fathers and sons.
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*Turns out my lactation biology hat out-ranks my primatologist cap because I was so overjoyed by the breast/mammary distinction I magnanimously forgave her referring to the potto as “a monkey” instead of the strepsirhine it is.
Florence Williams’s book tour may bring her to your neck of the woods: Boston, New York, Washington DC, Boulder, Denver, Seattle, San Francisco, Salt Lake City.
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Florence Williams. 2012. Breasts: A Natural and Unnatural History. Norton.
Andrew P. Tharp, Maricel V. Maffini, Patricia A. Hunt, Catherine A. VandeVoort, Carlos Sonnenschein, and Ana M. Soto. 2012 Bisphenol A alters the development of the rhesus monkey mammary gland. PNAS. Early ViewDOI:10.1073/pnas.1120488109
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