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 study published in February 2012.
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 we’ve seen a rise in childhood obesity. But he was quick to point out that there are “definitely limits to how much you can say to that.”
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 has developed, 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.”