Single Dose Lab Tests Underestimate Bisphenol A Exposure
COLUMBIA, Missouri, June 20, 2011 (ENS) – Exposure to the chemical bisphenol A through diet has been underestimated by previous lab tests, finds new research from the University of Missouri.
BPA, a chemical used in plastics and in the lining of food cans, is pervasive in the environment and has been found in most water sources worldwide.
Studies have established that BPA mimics the female hormone estrogen, and in so doing it disrupts the bodys endocrine processes. BPA is suspected of involvement in prostate cancer, breast cancer, and autism.
Research conducted by Bond Life Sciences Center investigator Cheryl Rosenfeld challenges the accepted method of administering bisphenol A in research studies by means of a single oral dose. Hers is the first study to examine concentrations of BPA in the blood of any research animal after being exposed through a daily diet.
Rosenfeld says single dose studies do not accurately reflect exposure to BPA in real life situations, so the research results are likely underestimating the amount of BPA that might accumulate in the body.
Rosenfeld, an associate professor in biomedical sciences, conducted the first study to examine concentrations of BPA in animals after exposure through a regular, daily diet, which she says is a better method to mirror the chronic and continuous exposure to BPA that occurs in animals and humans.
“People are primarily and unknowingly exposed to BPA through the diet because of the various plastic and paper containers used to store our food are formulated with BPA,” Rosenfeld said.
“We know that the active form of BPA binds to our steroid receptors, meaning it can affect estrogen, thyroid and testosterone function. It might also cause genetic mutations,” she said. “This chemical can hinder our ability to reproduce and possibly cause behavioral abnormalities that we are just beginning to understand.”
Mice fed BPA in their diet had higher blood concentrations than those given a single dose. (Photo credit unknown)
In the study, published in the June 6 issue of the journal “Environmental Health Perspectives,” Rosenfeld and her team continuously exposed mice to BPA through their feed, which is considered the primary route of exposure to this chemical in animals and humans.
As a result, more of the active form of BPA was absorbed and accumulated by the animals, the study showed. The active form of the chemical poses the greatest threat as it is the form that can bind to sex steroid receptors and exert adverse effects, Rosenfeld said.
The study notes that more than eight billion pounds of BPA are produced every year, and more than 90 percent of people in the United States have measurable amounts of BPA in their bodies.
“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 toxic substance,” said Rosenfeld.
“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.
“We need to study this further to determine where the ingested BPA becomes concentrated and subsequently released back into the bloodstream to be distributed throughout the body,” she said.
Specifically, Rosenfeld’s research is challenging the dosing method used in an often-cited 2002 study of BPA exposure and blood concentrations in human subjects.
Conducted by German researcher Wolfgang Völkel at the University of Würzburg, this study is considered a cornerstone for current U.S. Food and Drug Administration guidelines on acceptable BPA exposure for humans.
Völkel found the liver removes more than 99 percent of BPA from the blood, and humans excrete it within six hours. He did find some BPA in the blood of his volunteers but found this level to be insignificant.
But Völkel gave his research subjects a one-time dose of BPA, in the form of a hard gelatin capsule taken orally.
In her research, Rosenfeld measured BPA blood concentrations in mice exposed with the traditional method, a one-time oral dose. She then compared the blood concentrations of mice which were exposed to BPA continuously through a diet supplemented with this chemical.
The experiment was designed so that both sets of mice would receive the same concentration of BPA per body weight. However, in reality, Rosenfeld said, those exposed to a single oral dose ended up receiving a higher concentration than those exposed through diet.
Mice were tested at one hour, four hours, six hours, 11 hours, 24 hours and at seven days after beginning to consume the BPA-supplemented diet.
For the mice consuming the single oral dose, Rosenfeld’s findings were consistent with the 2002 findings and with other studies that have used this method of exposure. By 24 hours, the mice had excreted most of the BPA.
Not so in the case of the mice continuously consuming BPA in their food. At the end of 24 hours, Rosenfeld’s results were on par with the 2002 study, with most of the BPA being metabolized and excreted.
But seven days later this group of mice had higher BPA concentrations than they did at the 24-hour timepoint. This concentration was higher than in the mice consuming the single oral dose, even though the oral dose group ended up being exposed to a higher overall concentration per body weight than was the diet-only group.
This finding suggests that continuous and chronic dietary exposure to BPA results in accumulation of unconjugated BPA in the body, Rosenfeld said.
For Gail Prins, a professor in the departments of urology and physiology at the University of Illinois at Chicago, Rosenfeld’s result served as inspiration to revise her own BPA research.
Prins conducts research on effects of BPA on the prostate gland. Within the last year, she has published a paper comparing one-time oral dosing of BPA to placing the chemical in subcutaneous tissue.
Prins said, she was interested to learn that blood concentrations of the bioavailable form of BPA became higher when daily diet was the source, even though total BPA consumption was a bit lower in the mice dosed in food versus those given a single oral dose.
“I found that to be utterly fascinating,” Prins said. “Maybe what is bioavailable is being underestimated.”
BPA is primarily used to harden plastics, and is found in products such as eye glasses, gasoline containers, computer CDs, water supply pipes, and a variety of food packaging. It adds durability, clarity, and impact-resistance to plastic products. Recycling symbol “7” indicates BPA content.
Several studies show that BPA easily breaks down when heated, and small quantities are nearly ubiquitous in streams and in drinking water supplies in and near developed areas.
Tests by the Centers for Disease Control in 2004 showed traces of BPA in the urine of some 95 percent of Americans.
Food and drink containers such as hard plastic water bottles, baby bottles, and thin plastic film liners for steel food cans and aluminum soda cans are under the greatest scrutiny as BPA sources.
Also considered to be possible sources of human exposure are household dust and cigarette smoke, Rosenfeld said. BPA also might enter the body by way of dental sealants, water supply pipes, liners for water storage tanks, and thermal carbonless paper, which is used for cash register receipts.