Impact of race

In the study of body mass and BPA data from 2,838 youths aged 6 to 19, only white children were found to have significant increases in obesity prevalence as their BPA levels increased. Those with the highest concentrations in their urine were five times more likely to be obese than children with the lowest levels.

Black children with higher BPA levels were 1.25 times more likely to be obese than those with lower levels, which the scientists said is not statistically significant. Hispanic children had the same rates of obesity at the highest and lowest levels.

"Neither Hispanic (Mexican American and other Hispanic) or non-Hispanic black children had a significantly increased risk of obesity with elevated concentrations of urinary BPA," the authors wrote in the journal article.

It is unclear why BPA levels were so strongly associated with obesity in white children.

"There were no dietary differences specific to whites," said Dr. Leonardo Trasande, an associate professor of pediatrics, environmental medicine and health policy at NYU School of Medicine who was lead author of the paper. "It is possible that there is some genetic interaction that may be specific to the [white] population ... but we don't know."

It's also possible, he said, that higher rates of obesity in the Hispanic and black children – 23 and 24 percent, respectively, compared with 15 percent of white children – made it more difficult to tease out a link between the chemicals and obesity in those groups.

Challenged findings

Representatives from the chemical industry said the study had too many weaknesses to prove any connection.

Steven Hentges, from the American Chemistry Council's Polycarbonate/BPA Global Group, said that attempts "to link our national obesity problem to minute exposures to chemicals found in common, everyday products are a distraction from the real efforts underway to address this important national health issue."

The median BPA urinary concentration for children in the study was 2.8 nanograms per milliliter, slightly higher than the median for U.S. adults, according to a 2008 national survey by the Centers for Disease Control and Prevention. The highest group of children had concentrations at least double that.

Experts suspect that diet is the most frequent route of exposure for children. One study of 257 preschoolers in North Carolina and Ohio found that 99 percent of BPA exposure was through food. But national data is lacking and it is hard to pinpoint exposure since the chemical is in many plastics and other products.

The study adds to the evidence that certain industrial chemicals – called obesogens – may be in part spurring the obesity problem in the U.S.

"People are always told if you just stop eating or exercise more, you will lose weight. But there may be more to it ... and I think there is," said Retha Newbold, a visiting scientist at National Institute of Environmental Health Sciences who specializes in BPA and other endocrine-disrupting chemicals.

A life sentence

Human studies are limited. However, data from 3,967 adult U.S. men and women showed an association between higher BPA levels and obesity, regardless of race or gender, according to a study published in July 2012. The same association was found in Chinese adults in a recent study published in February.

In addition, baby rats exposed to BPA had increased body weight even though they were fed a normal diet, according to an August 2011 study. In the same study, the results of obesity were exacerbated when the rats were fed a high-fat diet and exposed to BPA.

The jury is still out on how a chemical like BPA would spur obesity, Newbold said.

"There are a lot of hypotheses floating around," Newbold said. "It's possible that it (BPA) alters neural development, which has been shown in rodents, and it increases their craving for sugar."

Most research on environmental chemical-induced obesity is focused on altered brain development, Newbold said.

"We're just now really digging into this stuff," she said.

It is difficult to investigate effects such as obesity because BPA doesn't stay in the body long. Since exposure comes from foods, however, BPA is continuously present in most people's bodies, Trasande said.

The new study found that compounds similar to BPA – other phenols, often in products such as sunscreens or soaps – were not linked to obesity in the children. They also controlled for activity level, calorie intake, tobacco exposure, race and education levels of whomever takes care of the child.

About 12.5 million, or 17 percent, of U.S. children are obese, which can lead to high blood pressure, diabetes and breathing problems. Obese children also are more likely to become obese adults.

"When a child becomes obese, it's a life sentence," vom Saal said. "It's not something the medical establishment has found a way to treat."

Trasande pointed out that 1,000 to 3,000 new chemicals have been produced every year since the 1970s, and at the same time a rise in childhood obesity has been observed. But he was quick to point out that there are "definitely limits to how much you can say to that."

Limited research

Chemical industry representatives remain skeptical.

"Due to inherent, fundamental limitations in this study, it is incapable of establishing any meaningful connection between BPA and obesity," said Hentges of the chemical industry group. "In particular, the study measures BPA exposure only after obesity hasdeveloped, which provides no information on what caused obesity to develop," he said.

Jennifer Wolstenhome, a University of Virginia postdoctoral fellow who studies endocrine disruption, said the study was strong, but noted that one limitation is the age range, which "spanned critical windows of development," including puberty.

Since children's bodies undergo many changes during those years, it could skew the results. For example, the chemical may affect children in different ways during or after puberty, when hormones change.

Trasande said he'd like to further this research by doing a longer term, population-based study on BPA looking at exposures even earlier in life and the potential for obesity, since susceptibility for infants is high.

"Poor diet and activity level certainly matter, but we need to be looking at environmental chemicals' role in obesity too," Trasande said. "Our study suggests we should reconsider the uses of BPA in the context of these new findings."

BPA is a main ingredient of polycarbonate, the hard, rigid plastic used in some food and water containers, as well as resins in the liners of some canned food and beverages.

Currently 11 U.S. states have banned BPA in some products, and in July the U.S. Food and Drug Administration banned the chemical from baby bottles and sippy cups.

The FDA rejected a petition from the Natural Resources Defense Council to ban BPA in food containers but says it is awaiting results of government studies into its potential health risks.