Researchers say unhealthy diets and lack of exercise aren’t the only culprits in obesity. BPA may share some of the blame.
In the latest study involving the plastic additive bisphenol A, or BPA, scientists found that children harboring higher levels of the endocrine-disrupting chemical in their bodies were more likely to be obese compared to youngsters with lower levels of BPA.
The report, published in the Journal of the American Medical Association’s theme issue on obesity, was led by Dr. Leonardo Trasande, an associate professor of pediatrics and environmental medicine at New York University School of Medicine. Trasande and his colleagues reviewed data on body mass index (BMI) and BPA exposure (determined by measuring the chemical in urine) in 2,838 children aged 6 through 19, who participated in the government’s National Health and Nutrition Examination Surveys (NHANES) between 2003 and 2008. About 34% of the children were overweight and 18% were obese.
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Those in the highest quartile of BPA exposure also had the highest rate of obesity, at 22.3%, while those with the lowest levels of the chemical in their urine were least likely to be obese, at 10%. That’s more than a doubling of obesity risk among those with the highest BPA exposure.
“It’s a very strong association, surprisingly strong,” says Trasande, “and it cuts across all socioeconomic strata. Unhealthy diet and lack of physical activity are major contributors to childhood obesity in the U.S., but this study shows that we need to consider environmental factors as a third major factor contributing to the epidemic.”
BPA is ubiquitous in our environment, found primarily in plastics used in food packaging and the liners of aluminum cans; it’s also found in dental fillings and sealants and coating thermal receipts used in stores. A government study found that 93% of Americans over age 6 have some detectable amount of BPA in their urine, and according to a comprehensive 2007 study among preschool children in North Carolina and Ohio, about 99% of children’s exposure to BPA comes from the diet. That’s why concerns over BPA leaching from plastics in baby bottles and sippy cups led the Food and Drug Administration to ban the chemical from these products in earlier this year. The agency stopped short of removing BPA from cans and other food packaging, however, citing the lack of definitive evidence of its health harms. (In 2010, Canada not only banned BPA from baby bottles, but also took the additional step of declaring the chemical toxic for human health, which make sit easier to remove the chemical from other food-contact products.)
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Trasande says the current findings question that decision, since it establishes a potential metabolic link between exposure to the chemical and obesity, which can lead to a host of chronic conditions, from heart disease to diabetes and asthma. But while the study establishes a link between the two, it doesn’t make clear in which direction the relationship operates. It’s possible, for example, that rather than BPA exposure contributing to obesity, it may be that obese children are simply consuming more foods high in BPA, such as canned sodas or microwavable products. But Trasande says this scenario is less likely, since he and his colleagues saw the strong correlation between BPA and obesity among children who consumed either more than the average number of calories each day or less. The connection also remained strong after the researchers adjusted for the amount of TV the youngsters watched.
The other explanation might be that exposure to the chemical, which has been shown to disrupt hormone levels, somehow interferes the young body’s still-developing ability to offset calories coming in with those being burned off, leading to an imbalance that favors weight gain. “Either way,” says Trasande, “this association raises further concerns for child health consequences associated with BPA exposure. [In addition to the risk of obesity], we know at least one study in which BPA is associated with impacts on brain development. And BPA may also affect a child’s lung development.”
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Interestingly, the association between BPA and obesity was strongest in whites than in any other racial or ethnic group. Since the NHANES data did not indicate any significant differences in the way participants ate, the researchers believe there may be some gene-based difference that makes Caucasian populations more vulnerable to the chemical.
Although BPA has a half-life of anywhere from 4 to 43 hours — meaning that half of any ingested amount is cleared from the body within that time — recent studies are starting to show that if the chemical is pulled into fat tissue, it may not be removed as quickly. People who have fasted for longer than this time continue to harbor high levels of BPA.
Taken together, the available data suggest that exposure to BPA may be an important contributor to obesity in children, and potentially put them at higher risk of chronic diseases such as diabetes, heart problems and liver failure. Studies in adults have linked higher urinary concentrations of BPA with these conditions. “This study suggests that we need to reconsider the recent choice not to ban BPA in cans,” says Trasande, especially since there are alternatives to making cans safer.
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Alice Park is a writer at TIME. Find her on Twitter at @aliceparkny. You can also continue the discussion on TIME’s Facebook page and on Twitter at @TIME.