Thursday, September 23, 2010

Study: Human Exposure to BPA 'Grossly Underestimated'

Americans are likely to be exposed at higher levels than previously
thought to bisphenol A, a compound that mimics hormones important to
human development and is found in more than 90 percent of people in
the United States, according to new research.

U.S. EPA says it is OK for humans to take in up to 50 micrograms of
BPA per kilogram of body weight each day. The new study, published in
the journal Environmental Health Perspectives, suggests that we are
exposed to at least eight times that amount every day.

"Our data raise grave concern that regulatory agencies have grossly
underestimated current human exposure levels," states the study.

The study also gives the first experimental support that some BPA is
likely cleared at similar rates in mice, monkeys and humans, making it
possible to extrapolate health studies in mice to humans.

Despite decades of research, questions about BPA have lingered and
recently become politicized. Sen. Dianne Feinstein (D-Calif.) hopes to
add an amendment to the "FDA Food Safety Modernization Act," currently
under consideration in the Senate, banning the chemical from
children's food and drink packaging. Republicans and industry
representatives have been averse, saying that research has not shown
conclusively that the chemical is harmful.

Hormones are essential during development and can determine, among
other things, a child's gender. BPA, since it mimics estrogen, is an
"endocrine disrupter," according to Thomas Zoeller, a biology
professor at the University of Massachusetts, Amherst. And amazingly,
BPA has the ability to bind to not one, but three receptors -- the
estrogen, the male hormone and the thyroid hormone receptors, Zoeller

Controversy over method

Some scientists question whether the ability of BPA to bind receptors
translates to a health effect. Detractors say that most of the
chemical does not circulate in blood long enough to have health
effects. All scientists agree that BPA resembles estrogen, and indeed,
it was first synthesized as a man-made estrogen substitute before
being used widely in the linings of canned goods and polycarbonate

Within the scientific world, the controversy hinges on the seemingly
obscure question: Does the liver detox the chemical completely enough
to secrete most of it out in urine, or does BPA get into human blood
where it can mimic important hormones?

Feeding human volunteers a fixed dose of BPA and sampling their blood
to check for the chemical would answer some of these questions,
according to Zoeller. But such an experiment throws up ethical issues.
The only human study of this nature was conducted in 2002 by the
German researcher Wolfgang Völkel at the University of Würzburg.

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.

It is at this point that science breaks down into controversy. Some
researchers say the method Völkel used to measure BPA in the blood was
not sensitive enough and that he likely overestimated the ability of
the chemical to pass through without causing harm.

The new study, led by Julia Taylor, a biologist at the University of
Missouri, uses a more sensitive test for measuring the compound. She
fed mice and monkeys a fixed amount of BPA daily. She took blood
samples and found that the animals had "biologically active" amounts
of the estrogen-like chemical, according to the study.

The study suggests that BPA is not completely removed by the liver and
does circulate in the blood and in amounts that are cause for concern,
according to Taylor.

"For those of us who work with BPA, no one has actually directly
compared mice and monkeys before, and monkeys and humans before,"
Taylor said. "For those of us who work with it in an academic sense at
least, this is confirmation of what we believe."

This study suggests that all the possible ways in which humans are
exposed to BPA are not yet known, Taylor said. It also makes it
possible to compare studies of BPA in mice and extrapolate it to
monkeys and humans since they all clear BPA at similar rates, she

"These data should make us reconsider some previously held hypotheses
about BPA, such as how quickly it is cleared from the body and the
differences in metabolism between species," said Linda Birnbaum,
director of the National Institute of Environmental Health Sciences.
"The paper emphasizes the need to better understand all the potential
sources of human exposure."


While some scientists found Taylor's method elegant, others such as
industry-associated scientists Julie Goodman and Lorenz Rhomberg, both
principals at Gradient, were not convinced. Rhomberg pointed out that
Taylor had not measured blood samples in humans herself.

He also said the human blood values that she used come from studies
where the samples were contaminated.

Taylor countered that she did not feel it ethically correct to conduct
experiments on humans, and Völkel had in fact removed any background
noise due to contamination from his results.

Gary Ginsberg, professor at the University of Connecticut and the Yale
School of Medicine, said that the study was a good first step that
addressed some of the controversy surrounding BPA degradation.

"It is a good exposition of data in primates that shows
pharmacokinetics in administered and controlled situations," Ginsberg
said. He said that more studies and an even more refined method of
measuring BPA in blood would be better.

Zoeller at the University of Massachusetts, Amherst, said that this
study provides some evidence that the liver allows some BPA to get
into blood and that our exposure to the chemical is greater than
previously thought.

"The body evolved to handle stuff that gets into our system -- the
liver is designed to detoxify," he said. "There are a range of
molecules that are natural, and some are incredible toxins. But when
we start to make molecules that are not known to nature, we need to
think a little more carefully about how they are going to interact
with biological systems."


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