A new University of Missouri study has found a “significantly greater” increase in the active form of bisphenol A in mice fed a steady diet supplemented with the compound, as compared with mice given a single oral dosage of BPA.
“Not surprisingly they found some differences between dietary and [single] dosing and report that dietary exposure is the better way to do the studies — to better simulate how people are exposed,” said Steve Hentges, executive director of the polycarbonate/BPA global group of the American Chemistry Council in Washington. That is “not exactly earth-shattering news,” he added.
The mice in the study were given a diet with 100 milligrams of BPA-d6 per kilogram feed weight for one week, compared with the 20 mg/kg body weight single dose of BPA-d6 that typically has been given to mice in lab studies.
The study, published online June 6 in Environmental Health Perspectives, a peer-reviewed journal published by the National Institute of “Environmental Health Sciences,” said these new results suggest that previous lab studies underestimate the level of dietary exposure to BPA.
“We believe that these mouse model studies where the BPA exposure is through the diet is a more accurate representation of what happens to BPA as the human body attempts to processes this ... substance,” said the study's lead author, Cheryl Rosenfeld, who is an associate professor in biomedical sciences and a bond life sciences investigator at the University of Missouri in Columbia.
“When BPA is taken through the food, the active form may remain in the body for a longer period of time than when it is provided through a single treatment, which does not reflect the continuous exposure that occurs in animal and human populations,” she said.
However, Hentges said that in order to properly assess the results of the study, it is important to look at the level of “free” BPA in blood, that is, the unmetabolized and biologically active form of BPA.
“With a dietary dose of 13 milligrams/kg body weight, they report a maximum level of free BPA in blood of 18.8 parts per billion,” Hentges said. “As the authors note, the disposition of BPA is linear over a wide range of doses, meaning that the level of free BPA in blood would be proportionally lower with a lower dose.”
Nevertheless, Rosenfeld noted that “the active form of BPA binds to our steroid receptors, meaning it can affect estrogen, thyroid and testosterone function, [which] can hinder our ability to reproduce and possibly cause behavioral abnormalities.”
Various previous studies have linked increased BPA exposure to breast cancer, infertility and early puberty. “People are primarily and unknowingly exposed to BPA through the diet because of the various plastic and paper containers used to store our food [that] are formulated with BPA,” Rosenfeld said.
However, it's Hentges' view that “some of the results are counterintuitive [and] based on very limited data.”
“The authors can only speculate why, but it is not clear these results are significant from an overall safety/risk perspective,” Hentges said. “And, consistent with other studies, they find that BPA is efficiently metabolized to a biologically inactive form and rapidly eliminated from the body with either form of dosing.”
Critically, he said, typical human exposure to BPA is 100,000 to 1 million times lower (less than 50 nanograms/kg body weight) than the dose used in this study.
“The level of free BPA in blood with a realistic dose would thus be less than one part per trillion,” Hentges said. “That level would not even be detectable and it would be hard to argue that it is a health concern. This all highlights how efficiently BPA is metabolized and cleared, which we already know. As a result, the relatively subtle differences found in this study may be scientifically interesting, but do not raise any health concerns.”
Funding for the study was provided by a grant from NIEHS, which is part of the federal Department of Health and Human Services.
Baby bottles that contain BPA already are banned in seven states: New York, Connecticut, Wisconsin, Washington, Maryland, Vermont and Minnesota; four counties in New York: Albany, Schenectady, Suffolk and Rockland; and the city of Chicago.
All major baby-bottle manufacturers that sell into the U.S. market said in 2009 they would stop selling baby bottles that contain BPA.
In addition, a ban on the sale of polycarbonate baby bottles containing BPA went into effect June 1 in the European Union. Canada has had a ban on BPA bottles for two years and last October declared BPA a toxic substance and is developing regulations to manage the risks from BPA. Also on June 1, Beijing began banning the production of BPA-containing baby bottles and will ban the import and sale of such bottles starting Sept. 1.
BPA is used to make PC and epoxy resins. The materials are used to line metal cans and are found in thermal printer paper and some dental composites and sealants.
The number of BPA bans worldwide continues to rise even though an international panel from the World Health Organization said in November it “would be premature” to initiate any measures to manage potential risks to public health from BPA.
“Levels of BPA in the human body … are very low, indicating that BPA is not accumulated in the body and is rapidly eliminated through urine,” said WHO.
Those conclusions were reached by WHO just nine days after a peer-reviewed study published online in the scientific journal Environmental Science and Technology said BPA levels found in canned food — as well as fresh foods wrapped in plastic packaging in the U.S. — are nearly 1,000 times lower than the “tolerable daily intake levels” set by the U.S. Environmental Protection Agency and the European Food Safety Authority.
More than 8 billion pounds of BPA are produced worldwide every year.