Urine levels of the chemical bisphenol A, found in many plastics, are strongly linked to type 2 diabetes, heart disease and liver enzyme problems, a new study suggests. The study, which examined a representative sample of the adult U.S population, appears in the Sept. 17 Journal of the American Medical Association.
“This is good news and bad news,” comments Richard Stahlhut, an environmental health research fellow at the University of Rochester. “The good news is these are man-made exposures. If the findings hold up, we could get rid of BPA and hopefully people get better. The bad news is it would mean that our system by which we determine risk is really flawed. It’s evidence that the regulatory system is inadequate in very important ways.”
In August, the Food and Drug Administration issued a draft assessment of bisphenol A that decrees the chemical safe at current exposure levels. The FDA’s bisphenol A subcommittee discussed that draft assessment at a public briefing in Rockville, Md., on September 16, the same day as the new study’s release.
The study is based on the National Health and Nutrition Examination Survey, or NHANES, conducted by the Centers for Disease Control and Prevention. NHANES uses physical examinations, clinical and lab tests and personal interviews to get a snapshot of the health and nutritional status of the U.S. population. The recently released 2003–2004 NHANES provided scientists with the first large-scale data set on human urinary bisphenol A concentrations.
“This is CDC government data — it’s done with very, very strict criteria,” says Frederick vom Saal of the University of Missouri in Columbia, coauthor of an editorial accompanying the new study.
Bisphenol A is the starter material for many plastics, including those used in baby bottles, some dental sealants and the lining of aluminum cans. Production of the chemical worldwide has reached nearly 7 billion pounds per year.
Years of studies on laboratory animals have linked the chemical, which mimics the hormone estrogen, to liver damage, obesity, insulin resistance and a suite of reproductive problems. In April the U.S. government’s interagency National Toxicology Program issued a report acknowledging that “the possibility that bisphenol A may alter human development cannot be dismissed.”
“The FDA is now looking and they have decided BPA is not a problem, in spite of the evidence for harm gathered in animal studies. I think this paper argues otherwise,” says Ana M. Soto, an endocrinologist at Tufts University School of Medicine in Boston.
The new study gauged bisphenol A levels in the urine of 1,455 adults, aged 18 to 74. Data were adjusted for age, sex, smoking, education and other factors. People with the highest bisphenol A levels (in the top one-fourth of the study population) were more than twice as likely to have diabetes and heart disease as those with lower levels. Higher bisphenol A levels were also associated with abnormal liver enzyme concentrations.
“In one sense it is all a surprise — this is evidence from a survey,” says David Melzer, a public health physician and epidemiologist at the University of Exeter in England, who led the new study. While the links to diabetes and liver abnormalities are in line with animal studies, the link with heart disease is new, he says.
Based on the urine samples, the researchers estimate that the quarter of participants with the highest bisphenol A levels were probably exposed to an average of 50 micrograms a day, versus 10 micrograms a day in the lowest group. Those levels are far below those currently considered to be safe. In the United States and Europe, an exposure of 50 micrograms a day per kilogram of body weight is acceptable — thus a 143-pound adult could consume about 3,250 micrograms per day.
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Studies that find correlations cannot be interpreted as cause and effect, caution the researchers. “These are clues that now need to be followed up on,” says Stahlhut.
In the scope of human history, it is only recently that people have gotten so good at making chemicals, says Stahlhut. “It makes perfect sense that we would eventually stumble on a chemical that causes a lot of problems at low doses. BPA might turn out to be a big offender.”
At the FDA’s subcommittee meeting, FDA toxicologist Michelle Twaroski outlined the agency’s draft assessment, released in August, that decreed current bisphenol A exposure levels safe. The panel then heard comments from more than two dozen critics and supporters of the draft’s conclusions.
John Van Miller, a representative of a group of bisphenol A producers, called the FDA assessment “thorough, objective, transparent and strongly supported by scientific data.”
Diana Zuckerman, a doctor representing the National Research Center for Women and Families, voiced concern about the FDA’s estimates of how much bisphenol A might leach into canned baby formula. “There’s plenty of reason for concern,” Zuckerman said. “The FDA draws concern about safety from industry’s rose-colored glasses.
The subcommittee devoted the final hour and a half of the meeting to questioning an invited panel of scientists about which avenues of inquiry should be pursued to learn more about bisphenol A’s health effects.