Web edition: October 6, 2009
Print edition: November 7, 2009; Vol.176 #10 (p. 12)
Researchers have just linked prenatal exposure to bisphenol-A – a near-ubiquitous industrial chemical – with subtle, gender-specific alterations in behavior among two year olds. Girls whose mothers had encountered the most BPA early in pregnancy tended to become somewhat more aggressive than normal, boys became more anxious and withdrawn.
This is the first study to link human behavioral impacts with BPA, a common ingredient in hard polycarbonate plastics and the resins used in food-can linings. Emerging data from an unrelated research group points to another especially rich newfound source of BPA to which people unwittingly may be exposed: thermally printed cash-register receipts (see next blog).
At present, there’s no way to know whether the apparent behavioral impact of BPA exposures early in development will persist or disappear, says Bruce Lanphear of Simon Fraser University in Burnaby, British Columbia. But this epidemiologist, an author of the new study, says his worry is that if the kids don’t grow out of these behaviors – and indeed, the changes are expressed widely across a population – they could greatly increase the number of teens at risk for delinquency, say, or for one day needing medical treatment of depression or anxiety.
Further prompting concern that the associations are real, his team points out, are rodent studies showing aggression and hyperactivity in pups prenatally exposed to BPA.
Lanphear and his colleagues at Cincinnati Children’s Hospital Medical Center have been conducting a Health Outcomes and Measures of the Environment – or HOME – Study for several years. A primary focus has been the investigation of neurobehavioral risks posed by lead exposures early in a child’s development. For the study, moms were recruited early in pregnancy and then followed through their babies’ births. The children – now three to five years old – will continue to be followed into school age.
Joe Braun of the University of North Carolina in Chapel Hill, Lanphear and their colleagues (from Cincinnati and the Centers for Disease Control and Prevention) decided to also scout for signs of any BPA impacts within a subset of HOME participants: 249 randomly selected mother-infant pairs. The recruits tended to be middle class and well educated, Braun notes.
More than 99 percent of the pregnant women tested positive for BPA during at least one of three urine tests during pregnancy. Ninety percent of the samples overall contained detectable concentrations of the estrogen-mimicking pollutant. Those concentrations proved quite variable, but usually turned up in the low parts per million range. For unknown reasons, one mom’s values were off the charts at 1,250 ppm, Braun notes.
In a paper out today in Environmental Health Perspectives, Braun’s team reports that the higher a mom’s BPA levels were during her first 16 weeks of pregnancy, the more likely her child was to later show behavior somewhat atypical of its gender. Urinary BPA values later in pregnancy showed no link to behavior, Braun says, suggesting that the window of vulnerability to BPA’s neurological impacts may be very early. Perhaps even before some women recognize they’re pregnant.
The girls appeared somewhat masculinized, the boys a bit feminized. Then again, Braun points out, it’s possible the girls’ behavior reflected a defeminization or the boys a demasculinization. In other words, the production or action of their gender-establishing sex hormones.might have been blocked.
Girls whose mothers had the highest BPA exposures in early pregnancy tended to score high on the “externalizing” component of a test known as BASC-2, for Behavioral Assessment System for Children-2. It’s geared to young children and evaluates their tendency towards aggression and hyperactivity. Boys with the highest womb exposures to BPA tended to exhibit an increased “internalizing” BASC score. They were more likely to “be withdrawn or show depressive symptoms, or maybe complain about aches and pains – which is often a manifestation of anxiety,” Braun explains.
The trend towards a behavioral deviation from the norm in all of these kids was small, Braun says, perhaps 2 to 6 points (as measured on about a 100-point scale) for each 10-fold increase in mom’s urinary BPA.
That’s a magnitude of change similar to the subtle IQ drops attributable to environmental lead exposures in U.S. children, notes Lanphear. Yet when extrapolated across a population, the societal cost of those tiny IQ losses becomes staggering, his calculations indicate.
Measures of a mom’s exposure to cigarettes or lead at any time point did not correlate with her toddler’s later behavior, the researchers found.
And Braun cautions, it’s possible that the behavioral scores his team measured in kids most exposed prenatally to BPA actually reflect current exposures to toxic substances, including BPA. To test that, the research team collected urine from each youngster at ages one and two. Those samples are only now undergoing testing, Braun says.
NEXT: Concerned about BPA: Check your receipts
Braun, J., . . . and B. Lanphear. 2009. Prenatal Bisphenol A Exposure and Early Childhood Behavior. Environmental Health Perspectives (in press).