Today’s New York Times features an outstanding summary of current debates — political and scientific — regarding the health effects of the chemical bisphenol-A, or BPA.  The article, titled “In Feast of Data on BPA Plastic, No Final Answer,” was written by Denise Grady who writes a lot about science and medicine.  I’ve pasted a few snippets from the article below; you can read the article in its entirety here.
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The research has been going on for more than 10 years. Studies number in the hundreds. Millions of dollars have been spent. But government health officials still cannot decide whether the chemical bisphenol-A, or BPA, a component of some plastics, is safe. The substance lines most food and drink cans, and is used to make hard, clear plastic bottles, containers and countless other products. Nearly everyone is exposed to it.

Concerns about BPA stem from studies in lab animals and cell cultures showing it can mimic the hormone estrogen. It is considered an “endocrine disruptor,” a term applied to chemicals that can act like hormones. But whether it does any harm in people is unclear.

Where science has left a void, politics and marketing have rushed in. A fierce debate has resulted, with one side dismissing the whole idea of endocrine disruptors as junk science and the other regarding BPA as part of a chemical stew that threatens public health.

About half a dozen states have banned BPA in children’s products, and Senator Dianne Feinstein hopes to accomplish the same nationwide, with an amendment to the food safety bill scheduled for a vote in the Senate next week.

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In May, a White House task force on childhood obesity issued a report suggesting that BPA and certain other chemicals might be acting as “obesogens” in children — promoters of obesity — by increasing fat cells in the body and altering metabolism and feelings of hunger and fullness.

Perhaps not surprisingly, the issue of whether BPA is safe has become highly partisan.

Environmental groups and many Democrats want BPA banned, blaming it for an array of ills that includes cancer, obesity, infertility and behavior problems. Environmentalists think the United States should adopt the “precautionary principle,” a better-safe-than-sorry approach favored in the European Union. The principle says, in essence, that if there are plausible health concerns about a chemical, even if they are not proved, people should not be exposed to it until studies show it is safe. The United States takes the opposite approach: chemicals are not banned unless there is proof of harm.

Many Republicans, anti-regulation activists and the food-packaging and chemical industries insist that BPA is harmless and all but indispensable to keeping canned food safe by sealing the cans and preventing corrosion, and to producing many other products at reasonable prices. . . .

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The idea that drugs or chemicals could act like hormones emerged in the 1990s. Such effects can be subtle and delayed. Hormones act on receptors in cells, structures to which they attach — the standard comparison is lock and key — and orchestrate growth, differentiation and all sorts of biochemical activities. Many cells have receptors for estrogen, and BPA can bind to those receptors, though far less strongly than the body’s own estrogen can.

R. Thomas Zoeller, a biology professor at the University of Massachusetts, Amherst, said BPA could also bind to receptors for male hormone and thyroid hormone.

“I don’t know of a single other molecule that does this,” Dr. Zoeller said.

In people, the most notorious example of an endocrine disruptor is the drug diethylstilbestrol, or DES, which was given to pregnant women in the 1950s in the mistaken belief that it could prevent miscarriage. The drug turned out to be a disaster, causing vaginal cancers and reproductive problems in some of the women’s daughters, and abnormalities in the reproductive organs in some sons. But DES is a far stronger estrogen mimic than is BPA, and women were exposed to much higher levels of it.

Animal studies during the past decade or so began raising concerns about BPA, which is used to harden polycarbonate, a clear plastic that makes nice-looking food containers, bottles and sippy cups. It has been widely used since the 1960s and is also in some medical devices, dental sealants, thermal paper for cash register receipts and the epoxy resin that lines most food and drink cans. The United States produces about a million tons of it a year.

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Last year, a scientific group called the Endocrine Society issued a 34-page report expressing serious concerns about endocrine-disrupting compounds, including BPA, dioxins, PCBs, DDT, the plasticizers known as phthalates and DES.

The society has about 14,000 members from more than 100 countries, who work in medicine, biology, genetics, immunology, industry and other areas.

The report said there was strong evidence that endocrine disruptors could harm the reproductive system, causing malformations, infertility and cancer. It noted that the chemicals could affect all endocrine systems, and said there was mounting evidence for effects on the thyroid gland, brain, obesity and metabolism, and the body’s ability to regulate insulin and glucose levels. It also said that fetuses exposed to chemicals in the womb could experience effects later in life, and pass those abnormalities to future generations.

Scientists call such effects “the fetal basis of adult disease,” and say they probably result from epigenetic changes — meaning that the chemicals alter the functioning of genes, turning them on or off, but do not cause mutations, which are changes in the actual structure of the genes. Some scientists said that they had doubted that low doses could cause harm, but changed their minds after seeing the data.

“I was skeptical that there were effects that were repeatable,” said Gail S. Prins, a professor of physiology at the University of Illinois at Chicago, and an author of the Endocrine Society’s report. But in 2001 she was part of a panel that analyzed dozens of BPA studies for the National Toxicology Program. The panel had its own statistician reanalyze raw data from the studies to find out if the claims based on it were valid.

“I could see there was some consistent data,” Dr. Prins said. “I started thinking, ‘Hmm, maybe there could be something there.’ It was still curious to me. This is not a regular toxicant. It’s acting like a hormone, and hormones can act at extremely low doses. If you think the dose makes the poison, it doesn’t make sense. But if you think about it as a hormone — and I’m an endocrinologist — it does make sense.”

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Over the next few years, researchers hope to bring coherence to this confused and troubled field.

“This is a chemical we’re all exposed to, and I think that makes it incumbent upon us to study it,” Dr. Birnbaum said. “We really need to know what it might be doing, if anything.”

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