Breastfeeding, Brain Development and Chemical Poisons: Neuroscientist Michael Merzenich

Photo of Michael Merzenich

Michael Merzenich

In late April 2007, the results of a scientific study conducted on newborn rats at UCSF were announced online in the early edition of the Proceedings of the National Academy of Sciences.

UCSF press release.

There's nothing unusual in that, of course. UCSF scientists generate hundreds of articles every year. But there was something critically important in this study that every parent needs to consider. In short, should some women with a genetic history that includes family developmental disorders such as language impairment or dyslexia — or with male partners who have a similar genetic background — breastfeed their babies?

Senior author of the study Michael Merzenich, PhD, UCSF Francis A. Sooy, M.D., Chair in Otolaryngology, member of UCSF's W.M. Keck Foundation Center for Integrative Neuroscience and a scientist who pioneered the concept of brain plasticity, is quick to state that this study was only in rats.

But he is equally quick to suggest that the results should add to our worry about how chemical poisons such as PCBs and PCBEs (the latter are used primarily as fire retardants) in our environment can scramble a developing brain — and how the varying cognitive deficits we know as autism and Asperger's syndrome might be a consequence.

Merzenich understands that he is treading on very thin ice. The value and benefits of breastfeeding are well-known. And for a scientist to inject a disruptive theory into a maternal bonding experience is, he admits, presumptuous.

Yet he is alarmed. And he is not alone. The Department of Health and Human Services has posted lengthy documents here and here on its website about the harmful effects of PCBs and PCBEs.

So has Merzenich himself.

With hundreds of thousands of tons of PBDEs — chemical cousins of PCBs — accumulating in the environment every year and with levels rising in human fat tissue, it is very worrying to think that the levels of PCBs to which the laboratory rats were exposed proportionately equal the levels now being found in the breast milk of women all over the country. Again, studies in rats do not always correlate to effects in humans. That is why Merzenich is urging the government and disease-focused organizations to push harder for human studies.

Because the breastfeeding question is so important, we have created a 13-minute recording of Merzenich's Science Café interview and made it available through our podcast download site. Other portions of the interview, which covered everything from the aging brain to neural prostheses, will be made available in the coming weeks.

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Related Links

PNAS research pape
PNAS, April 25, 2007
Class of PCBs Causes Developmental Abnormalities in Rats
UCSF News Services, April 23, 2007
HH&S on PCBs
What underlies the documented increase in autism incidence? Results of a new study
Posit Science, April 26, 2007
Harnessing the Brain's Plasticity Key to Treating Neurological Damage
UCSF News Services, February 15, 2007
Grasping Autism
UCSF Magazine, December 2004



Podcast transcript

Jeff Miller: We've talked many times before about the impact of your work on the understanding of autism. Now that we have that very scary result PCB study in rats I'm wondering, should we be doing anything different? Should women stop breast feeding for example? What are the implications of that work?

Michael Merzenich: First of all the study is in rats. I've been trying to encourage the Autism Foundation and others to pursue correlative studies in humans. The Centers for Disease Control have been worried about these chemicals and their potential effects in the development of babies for a long time and since about 1999 or 2000 they have been issuing warnings about them both about PCBs and PBDEs. Their concern has been primarily about women exposed to these chemicals in areas where they are known to be in relatively high concentrations but, in general our study adds to the worry and it really indicates that it's in the great public interest to determine quickly whether or not these chemical poisons which are very widespread in the American environment, in the world environments, are adding to the risk of onset of these developmental disorders. Because if they are this is a big thing. Actually especially in the case of PBDEs: I should say that the PCB is a double ring organic compound and C stands for chlorine. It's a chlorinated compound and there is another family of closely related compounds in which the ring structures are brominated and not chlorinated. Those are the PBDEs. They are still being produced in the hundreds of thousands of tons as fire retardant chemicals and we know that the PBDEs have been growing and increasing in concentration in American females and in their milk ,doubling every two to five years. So they are still very rapidly increasing in concentration and actually the concentration is equal or past the level of concentration of PCBs.

Miller: Now PCBs if I remember correctly have been banned since the late 70s.

Merzenich: Right.

Miller: And the PBDEs continue to be produced as you just mentioned

Merzenich: Even though the PCBs were banned there was a large quantity produced and it's out there in the environment and its very very slowly degraded. And it actually accumulates in animal tissue and its basically lipidophilic so it's concentrated in animal fat and it basically has been growing in concentration. Concentration has increased up until recently even though it was banned a long time ago because it gradually accumulates and in mammals it's very, very difficult to get rid of it. It's not broken down effectively in the body so it accumulates slowly, increasing in concentration across the life span in humans...only relatively recently levels of PCBs recorded in human tissue in the US have been going down but, at the same time as they go down the PBDEs go up...

Miller: Do they work in tandem in some fashion?

Mrezenich: Well we don't really know too much about the biological impacts of the brominated family of compounds. They have been very little studied. Chemically and structurally, they are very, very similar to a sub family of the PCBEs and it's reasonable to believe that they have similar effects. Again the Centers for Disease Control have been worried about them for a while because there has been evidence growing that they have effects in child development. So we chose the particular PCB for study in part, because they are very structurally similar to these PBDEs, even though there is also a relatively high concentration in the environment as well.

Miller: Is there any way that we can protect ourselves since these compounds are so ubiquitous?

Merzenich: Well, it's a problem especially in the case of PBDEs because they are still being produced and released into the environment. The governments in the US and more aggressively recently in the rest of the world, especially in Europe and in Japan, have been trying to encourage industry to substitute. In some places in Europe, they have been banned for a while, and now there is a European Union- wide move to eliminate the release of PBDEs. There has been a growing movement to try to replace these fire retardant chemicals the PBDEs with something that is not so likely to be so biologically active. That is occurring slowly in products that have been produced in Japan, in the United States and in Europe. In part it's driven by the fear of the producers of these chemicals for the ultimate consequences of being held accountable for their massive release into human environments.

Miller: And what would be the association between the damage seen in rats and the potential damage seen in embryonic development of humans?

Merzenich: Actually we delivered it in rats. We attempted to simulate the levels that had been recorded in human females in American environments. The consequence of adding the PCB poisoning to simulating what we believed to be the factors that are contributing to the onset of these developmental disorders, autism and related disorders, had devastating additional consequences. So we saw brains that were more degraded in their organization developmentally in these rats than we have ever seen before. The PCBs had a very powerful amplifying effect for these developmental catastrophes that we were producing in these little animal models. It both degraded the normal development of the brain. It basically frustrated the brain so that processes were very abnormal and the brain remained into adulthood in a very primitive underdeveloped state. So there is no question that in these models that there was some powerful, some amplification of what would be contributed by an inherited weakness and that you would expect this, the agency of this poison to contribute to an increased risk in a genetically at risk individual for the onset of something worse and that could be the conversion of somebody that would otherwise be a child that would develop a milder impairment developing something like an autistic syndrome condition. It should be pointed out that it's not just, if there is any validity to this scenario, it's not just the fact that PCBs and PBDEs accumulate in the environment.

There is a second probable contributor to the problem and that's the increased rate of nursing and increased rate of duration of nursing in American populations. So over the past 30 years for very good reasons, for the health of infants, more and more mothers are nursing their babies. We have gone from a nursing rate of about 25 percent roughly a quarter of babies being nursed by their mothers to about 75 percent. The average duration that mothers nurse their infants now is about twice as great as it was 30 years ago. This is a positive and good and healthy thing. The problem is that these chemicals are concentrated in breast milk at a level of about six fold as they are in regular body tissues. Because they are concentrated in fat, in a sense the mother is concentrating these poisons and delivering them in relatively high dose levels to infants.

That is another way of saying that if this really is an agent that's contributing to the increased risk for these catastrophic developmental conditions, then a mother that has inherited weakness probably should think about this possibility when thinking about breastfeeding her infant. So all of the wonderful good and positive reasons for nursing your baby, those are all real, those are all terrific, they are all for the good of the baby unequivocally. It's very hard to speak against that or be discouraging about that but, on the other hand, there is the possibility that in nursing you actually increase the risk of a bad outcome in this respect.

Miller: How would a mother know whether or not she has an inherent weakness?

Merzenich: Well, it's a problem and I think what's going to happen, well first of all you know that you have an inherent weakness, potentially, because there is autism or developmental disorder in your family. So, if your family has a history of language impairment or of dyslexia or of autism itself, those would certainly be indications that you probably have, or the husband, it can come from either side, or both -- it would be an indication that there is some reason for concern. Maybe genetic screening on some level is called for; genetic counseling is called for, for the parents in such a case.

Miller: Have you shared this opinion, have you spoken out about it or written about it and then been confronted by those who feel that this is an attack on breast feeding?

Merzenich: I've tried to be precautious about it but, on the other hand, what do you do when you have a hot potato like this in your hands? I mean on the one hand you don't want to be an alarmist on the level which it can cause or going to result in an exaggerated and ultimately destructive response. Because, we know there is a lot of powerful evidence about the healthful benefits the good and positive benefits of child development for breast feeding not to mention the attachment of the mother with the infant and all these other wonderful and positive things that are associated with it. It is absolutely with great trepidation and with substantial reservation [that I discuss the potential role of breastfeeding]. Remember that this is a rat study, and basically on the basis of the study alone, giving any kind of advice to a mother or a pregnant woman about whether or not they should nurse their baby is very presumptuous. Really what these studies strongly indicate is that they again raise a caution, a red flag, a warning and what we've tried to argue is that we know to little to be sure about it. But, this unequivocally raises a concern, a concern that we hope will be aggressively addressed by other scientists and by the government. Ultimately it might mean that you might not want to just know whether or not you have genetic risk for the origin of something like autism but, you might want to know your PCB and PBDE levels in your blood and in your mouth and it might be of great interest to a young mother.

Miller: And are those tests are readily available?

Merzenich: No they are not readily available and this is one of the problems, I think they will become more readily available and right now it's a scramble and a struggle. It's not that these measurements are so difficult to make. The government in fact is monitoring the concentration of these chemicals in areas in which they believe individuals are at risk. In various ways, looking epidemiologically, trying to get the ultimate consequences in human populations of there being high levels of these concentrations in breast milk and in blood. It's still very piecemeal and fractionated and it's not something that is easily and readily available for the average mom.