Tuesday, December 08, 2009

Plastic Makes Boy's Brains and Play Less Boyish? What Do Phthalates, Phallic Fears, and the Supreme Court All Have In Common?


Phthalates in pregnancy feminize the developing male brain rendering boys less boyish. 

So says University of Rochester researcher Shanna Swan who found women who had high levels of the chemical in their urine during pregnancy later reported their boys showed less masculine play.  

But who cares...

Let's not waste too much time on that study - it's correlational in nature and riddled with methodological pot holes.  And because I've just read  Randy Olsen's Don't Be Such a Scientist, I'm not gonna bore you with the technical details. 

Not when the back story on researcher Shanna Swan is so much juicier, so much more newsworthy, clearly what we science-minded people need to focus on if we're ever gonna patch up the poor science in the media let alone convince parents their children are not endangered by plastic. 

So the dirt comes from Trevor Butterworth, the editor over at STAT.org, in his regular column at Forbes.com (Can Plastic Change Your Sex?: Another weak claim consumes the media).  Butterwoth blames some of the current plastic panic on a 2005 study by Swan. 

Yes, the original fallacious and phallic phthalate study:  
..Swan claimed that levels of certain phthalate metabolites in pregnant women correlated with a lower anogenital index in their male children (the AGI is a measurement of the distance from the anus to the base of the penis, divided by the weight at the time of measurement). 
There wasn't a consensus as to what a normal range for AGI was in baby boys or whether it is significant, but there was evidence that a shorter AGI correlated with a slower rate of testicular descent in animals. When a National Institutes of Health expert panel later evaluated her study, it didn't find her evidence wholly convincing. All the babies in the study had normal genitalia with no sign of defects.
The lack of penile imperfections didn't stop Swan from publicly declaring phthalates in utero cause genital malformations AND birth defects in boys.  Human boys.  Without any evidence!  Well, in fact, with evidence suggesting the contrary.  But of course that didn't stop the media and environmental activists (nor legislators) from proclaiming phthalates a dangerous toxin.  And now said researcher is pushing more bad science and claiming she's got evidence that phthalates feminize the brain. 

But that's not the end of our story.  Swan also has testified as an expert witness in at least two court cases for plaintiffs claiming harm from toxic substance, one, an anti-nausea drug, the other, silicone breast implants.  In both cases the courts actually invalidated her expert testimony.  In fact, her scientific nonsense not only reached the Supreme Court (yes!) but troubled our Supreme Justices so much they decided to redefine what constituted good scientific testimony.   Now that's impressive.  Offending the Supreme Court with your lousy empirical arugments.

So of course that information went missing from the media coverage of Swan's latest phthalate study:

Why You Need to Avoid Phthalates: Baby Boys Are Found to be Affected by Chemicals in Plastic (Babble.com, Dec. 7, 2009)

Common Chemical Making Boys Soft  ABC News (November 17, 2009)

Phthalates Affect Way Young Boys Play: Boys With High Phthalate Exposure in Womb Show Less Masculine Play (WebMD.com, November 16, 2009)

If only the latest pseudo scientific study were Swan's swan song to parents...

Prenatal phthalate exposure and reduced masculine play in boys.  International Journal of Andrology.  Published online November 16, 2009.   DOI: 10.1111/j.1365-2605.2009.01019.x

2 comments:

rich winkel said...

"normal genitalia with no sign of defects" ... "normal" is a highly subjective measure given the variations in people's private parts. At some (fairly arbitrary) boundary variation becomes defect. But in any case she wasn't claiming the existence of defects, she was using the AGI as a sensitive quantitative measure of an overall shift in the distribution (some of which might reach into the area of defect) which was correlated with exposure to pthalates in other mammals, mammals which share a great deal of hormonal similarities with humans.

Ok, so the study is correlational (I assume the statistics are reasonably convincing). But isn't it true that pthalates mimic estrogen in the body, and estrogen is involved in the development of female sexual characteristics such as the AGI? It's conceivable that estrogen might also affect brain development, and might be largely responsible for the pronounced differences between boy play and girl play. Proof? No, just a correlation between pthalates and AGI in some mammals and a plausible mechanism connecting the AGI with brain development.

So this correlation corroborates what we already knew or could have plausibly argued (not proved) about pthalates and the AGI in humans. The second step, connecting estrogen with brain development is more speculative. Suppose there are no correlates connecting estrogen to human behavior and thus, in all likelihood, brain development (there ARE correlates, but for the sake of argument). So now we have a choice of what to recommend to someone who has no time to even ask such questions, a recommendation which we must make despite what is known (and unknown) about our own level of ignorance. Do we say it's ok to use pthalates in baby bottle nipples (for instance) or not? I would suggest that there's a simple resolution: if you, as an educated person who has time to research such things and who love your children like there's no tomorrow, would not wish to needlessly expose your children to such uncertainties and possible hazards, the same precautionary principle should also apply in your advice to others.

In the face of unavoidable ignorance it should not be necessary to prove harm in order to justify some level of precaution. Reasonable doubt should be sufficient. Otherwise I'd be out sampling random mushrooms on this wet foggy day.

Polly Palumbo, Ph.D. said...

Hi Rich,

I admire your tenacity! You've been busy today. Anyhow, I'm surprised you seem to heed the warning from this study - one of many studies that large numbers of scientists have deem flawed or biased. In your previous comments you point fingers at biased scientists. I would have thought you'd be suspicious of this kind of pseudo-science.

As you'll see from many of my posts, I do think we're overestimating many threats, and there are costs, sometimes significant societal ones, case in point, the increasing number of unvaccinated children.

As for the precautionary principle, I threw away the BPA bottles and less concerned than others about it, at least the media. I am also not convinced on the basis of the large body of science that phthalates are as toxic as the media would have us believe. I think it's perfectly fine to practice precaution while also questioning the science and the experts. I don't see a problem there.