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Chemicals May Play Role in Rise in Obesity

"Exposure to bisphenol A is continuous," said Frederick vom Saal, professor of biological sciences at the University of Missouri at Columbia. Bisphenol A is an ingredient in polycarbonate plastics used in many products, including refillable water containers and baby bottles, and in epoxy resins that line the inside of food cans and are used as dental sealants. In 2003, U.S. industry consumed about 2 billion pounds of bisphenol A.

Researchers have studied bisphenol A's effects on estrogen function for more than a decade. Vom Saal's research indicates that developmental exposure to low doses of bisphenol A activates genetic mechanisms that promote fat-cell activity. "These in-utero effects are lifetime effects, and they occur at phenomenally small levels" of exposure, vom Saal said.

Steven Hentges of the American Chemistry Council said his organization's review of the scientific literature found that a preponderance of the bisphenol A studies have shown no adverse effects, including no increased body weight. "Our conclusion is that there is no risk to human health," said Hentges.

But many scientists disagree, including vom Saal, who called the ACC's statements a "blatant lie."

Research into the impact of endocrine-disrupting chemicals on obesity has been done only in laboratory animals, but the genetic receptors that control fat cell activity are functionally identical across species. "They work virtually the same way in fish as they do in rodents and humans," Blumberg said. "Fat cells are an endocrine organ."

Ongoing studies are monitoring human levels of bisphenol A, but none have been done of tributyltin, which has been used since the 1960s and is persistent in the marine food web. "Tributyltin is the only endocrine disrupting chemical that has been shown without substantial argument to have an effect at levels at which it's found in the environment," Blumberg said.

Concern over tributyltin's reproductive effects on marine animals has resulted in an international agreement discontinuing its use in anti-fouling paints used on ships. The EPA has said it plans next year to assess its other applications, including as an antimicrobial agent in livestock operations, fish hatcheries and hospitals.

Bisphenol A is approved by the Food and Drug Administration for use in consumer products, and the agency says the amount of bisphenol A or tributyltin that might leach from products is too low to be of concern. But the National Toxicology Program, part of the National Institutes of Health, is reviewing bisphenol A, and concerns about its estrogenic effects prompted California legislators to propose banning it from certain products sold in-state, a move industry has fought vigorously.

Researchers said the next step is to learn if these apparent animal "obesogens" are affecting people.

"Our job is to follow the science, and based on these animal studies, this is worth taking a look at," said Heindel of the NIEHS.


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