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Now, to a new study about the plastic additive BPA. The research suggests a link between BPA and the epidemic of childhood obesity, but as NPR's Jon Hamilton explains, it's too soon to say BPA can cause kids to put on weight.

JON HAMILTON, BYLINE: BPA can act like estrogen in the body. And in recent years, environmental groups have suggested it can cause everything from ADHD to prostate disease. But the science behind those allegations tends to be inconsistent and hard to interpret. And that's the case with this new study from a team at New York University.

The team looked to see whether children and adolescents with higher levels of BPA in their urine were more likely to be obese. Leonardo Trasande says that at least with white kids, they were.

LEONARDO TRASANDE: Among the children with the lowest levels of BPA, 10.3 percent were obese. While among the children with the highest levels of BPA, 22.3 percent were obese.

HAMILTON: But among black and Hispanic children and adolescents, hired BPA levels were not associated with obesity. And in none of the groups was there an association between BPA levels and being just overweight, as opposed to obese.

Trasande says those seemingly contradictory findings make it hard to draw any conclusion.

TRASANDE: When we find an association like this it can often raise more questions than answers. Clearly we need a longer-term study that examines exposure in the earliest parts of life, to see whether BPA exposure then may lead to obesity in a child.

HAMILTON: Trasande says BPA is probably most likely in to cause long-term changes in children when they are still in the womb. But he says despite the caveats surrounding the new study, it may be time to rethink childhood obesity.

TRASANDE: Diet and physical activity are still the leading factors driving the obesity epidemic in the United States. Yet, the study suggests that we need to also consider a third key component to the epidemic: environmental factors that may also contribute.

HAMILTON: Other scientists say it's hard to interpret the results of the study, which is published in the Journal of the American Medical Association. Frederica Perera, who directs the Columbia Center for Children's Environmental Health, says the team has done good research but hasn't shown whether BPA is actually causing obesity.

FREDERICA PERERA: As they point out, obese children may be simply eating and drinking foods that have higher BPA levels.

HAMILTON: So does BPA make kids obese or do obese kids just take in more BPA when they eat and drink? There's no way to know from this study. And Perera says BPA may not be the only chemical that deserves scrutiny.

PERERA: Our center has recently published a study showing that prenatal exposure to another group of endocrine disruptors, polycyclic aromatic hydrocarbons, or PAH, was associated with obesity in the children.

HAMILTON: These hydrocarbons are found in air pollution.

Mike Dedekian runs a pediatric obesity clinic at the Barbara Bush Children's Hospital in Portland, Maine. He says the new study doesn't answer the question parents are probably asking.

MIKE DEDEKIAN: So does BPA cause obesity? We don't know yet. Does this study raise our level of concern? Yes, it does. And it means we need to go further in science to establish whether or not there is more to this than just an association.

HAMILTON: Dedekian says in the meantime, he hopes parents will stay focused on diet and exercise.

DEDEKIAN: For me, we've not reached that point yet where we're starting to across the board make recommendations to patients about which products or chemicals or plastics to avoid.

HAMILTON: Regulatory agencies seem to agree. The FDA did ban BPA from Sippy Cups and baby bottles this summer. But that came after the plastics industry requested the action, as part of an effort to reassure consumers. And the FDA rejected a call by environmental groups to remove BPA from all products that come in contact with food, saying the scientific evidence of harm just wasn't there.

Jon Hamilton, NPR News.

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