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(USA TODAY) --Kids with higher levels of the widely used substance BPA in their bodies are more likely to be obese, according to the first large-scale, nationally representative study to link an environmental chemical with obesity in children and teens.

Researchers acknowledge that their study's design doesn't allow them to definitely conclude that BPA, or bisphenol A, caused the children's obesity. Rates of obesity have been rising for three decades as Americans have become more sedentary.

But the findings, in today's Journal of the American Medical Association, add to a growing body of research -- in both humans and animals -- questioning BPA's safety, says Philip Landrigan, director of Children's Environmental Health Center at the Mount Sinai School of Medicine in New York.

"It's a credible study and it has to be given some attention," says Landrigan, who was not involved with the study.

In particular, the study adds to the notion that certain chemicals are "obesogens" that alter the body's metabolism, making it harder for people to lose weight, even with diet and exercise, says Linda Birnbaum, director of the National Institute of Environmental Health Sciences, who was not involved in the study.

"Are we programming people to fail?" Birnbaum asks. "That's the question we need to ask, instead of blaming people."

Exposure to BPA -- an estrogen-like chemical used in everything from plastic water bottles to the linings of metal cans and even the coatings on certain paper receipts -- is nearly ubiquitous. More than 92% of Americans over age 6 have detectable levels in their blood, according to the Centers for Disease Control and Prevention.

The new study drew on CDC surveys of 2,838 kids and teens, ages 6 to 19. Researchers found that more than 22% of those with the highest BPA level in their urine were obese, compared to 10% of those with the lowest levels.

A study published last year, also based on CDC data, found similar patterns of obesity among American adults exposed to BPA.

To make sure that their results were reliable, authors of the new study factored a number of important considerations into their calculations -- including the children's race, age, income, sex, exposure to tobacco, number of calories consumed each day, number of hours spent watching TV and their caregiver's educational level.

Their results held up only for white children, says Leonardo Trasande, the study's main author, of the New York University School of Medicine. In black and Hispanics, further analysis showed that the link between BPA and obesity could be due to chance.

The study's design doesn't allow researchers to definitively conclude that BPA made the children gain weight, Trasande says.

It's possible that obese children consume more BPA, such as through canned soda, Trasande says. It's also possible that obese children have higher BPA levels because the chemical is stored, and later released, from fat.

Taken alone, the study might not make much of a case against BPA, Birnbaum says. But it's more powerful in light of the long list of earlier experiments in animals and cells linking BPA to obesity, diabetes, breast and prostate cancers, behavior problems and other issues, especially in animals exposed before birth.

In recent years, evidence has linked BPA to a variety of human ailments:

-- A study published in Pediatrics last year found that girls exposed before birth to high levels of BPA were more likely to be anxious, depressed and hyperactive at age 3.

-- Men with higher levels of BPA were two to four times more likely than others to have problems with sperm quality and quantity, according to a 2010 study in Fertility and Sterility.

-- A 2008 study in JAMA linked high BPA levels in adults to diabetes, heart disease and abnormal liver function.

The Food and Drug Administration banned BPA in baby bottles and sippy cups in July. Environmental groups also have pressured the agency to reduce or eliminate other sources of BPA.

Pediatric endocrinologist Larry Deeb says the new study provides enough evidence for parents to act, in spite of its limitations.

He suggests that parents buy only plastic sports bottles that are BPA-free, and avoid buying canned soups and vegetables.

"The conclusion seems to be to avoid BPA as much as possible," says Deeb, who specializes in treating obesity. "Why do we have to expose ourselves to these things? Fresh or frozen fruits and vegetables are probably better for you, if you can afford them, which is always the rub."

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