TUESDAY, Oct. 6 (HealthDay News) -- In the latest study to suggest an association between the plastics chemical bisphenol A (BPA) and adverse effects on humans, researchers report that BPA may affect the behavior of little girls.
Girls exposed to higher levels of BPA displayed more "externalizing" behaviors, such as aggression and hyperactivity, according to the study, which is published in the Oct. 6 online edition of Environmental Health Perspectives.
"We found almost all of the women [in the study] had detectable levels of bisphenol A in at least one of the tests, and elevated concentrations were associated with externalizing behaviors in female children," said study author Joe Braun, a graduate student and research assistant in epidemiology at the Gillings School of Global Public Health at the University of North Carolina at Chapel Hill.
Not everyone agreed with the study's conclusions, however.
"This type of study has no capability to establish cause and effect, only associations. At the end of the study, the authors even point out that the results 'should be viewed cautiously,'" noted Steven Hentges, executive director of the polycarbonate/BPA global group at the American Chemistry Council, which represents the chemicals industry.
BPA is a commonly used chemical that's found in hard plastics and epoxy resins. The chemical is used in water bottles, food containers, infant bottles and medical devices. BPA may also be found in the lining of canned foods. Most human exposure comes through diet when the chemical leaches into food and beverages from the containers, according to the U.S. National Institute of Environmental Health Sciences. Previous studies suggest that more than 90 percent of people in the United States have detectable levels of BPA in their urine.
Animal studies of the chemical have found an association between BPA and adverse neurodevelopmental effects on fetuses and newborns, according to background information in the study.
The current study included 249 pregnant women from Cincinnati, Ohio, who were part of another study that was evaluating interventions to reduce lead levels. Urine samples were collected when the mothers were 16 and 26 weeks pregnant, as well as within 24 hours of birth.
Ninety-nine percent of the women had at least one urine sample with detectable levels of BPA, according to the study.
The children's behavior was reported by the parents using a standardized questionnaire when the children were 2 years old.
After controlling the data to account for numerous possible confounding factors, such as maternal age, race, education and income levels, the researchers didn't find an association between BPA and externalizing behaviors. However, when they split the data by sex, they noted an association between higher BPA levels and more externalizing behaviors in girls.
Braun said that the researchers don't know why there was a difference in the findings by sex, nor did they know what the potential biological mechanism might be that could cause an increase in aggressive behaviors after BPA exposure.
The researchers did not adjust the data in this study to account for lead exposure, diet or after-birth exposure to BPA. Braun said that the researchers did test additional statistical models to account for lead exposure that weren't included in the paper, and he said that when this was done lead levels didn't change their findings.
However, "once you consider the limitations of the study, as the authors carefully do, there's significant potential for false positives," contended Hentges.
Braun said that parents who are worried about the potential for harm can look for products that specify that they're "BPA-free." He said the chemical is found in many different consumer products and there are no requirements that it be listed on a label, so if a product doesn't clearly state that it doesn't contain BPA, it may be made with the chemical. One known source of BPA is plastics with the number 7 in the recycling symbol.
Learn more about bisphenol A from the U.S. National Institute of Environmental Health Sciences.
SOURCES: Joe Braun, M.S.P.H., graduate student, research assistant, department of epidemiology, Gillings School of Global Public Health, University of North Carolina, Chapel Hill, N.C.; Steven Hentges, executive director, polycarbonate/BPA global group, American Chemistry Council, Arlington, Va.; Oct. 6, 2009, Environmental Health Perspectives, online