The results "both support and extend the conclusion from the U.S. Food and Drug Administration that BPA is safe as currently used," says Daniel Doerge, a research chemist with the FDA's National Center for Toxicological Research.
Scientists agree that in large doses, BPA can act a bit like the hormone estrogen. But there's been a lot of debate about whether the tiny amounts found in people have the potential to cause problems.
BPA has received a lot of attention because the chemical leaches out of many products, including polycarbonate water bottles and the lining of metal food containers. As a result, "Nearly everyone in the U.S. will have traces of BPA in their urine," Doerge says.
So Doerge and his colleagues have been working with scientists from the National Toxicology Program at the National Institutes of Health to see if there are any effects from this low-level exposure.
In their most recent study, the researchers exposed rats to BPA starting a few days after conception and continuing through sexual maturity. Doses ranged from about 70 times the amount that Americans typically get through their diet to millions of times that amount.
And even when rats got more than 70,000 times what a typical American ingests, there was no change in body weight, reproductive organs or hormone levels, the scientists reported. "In the low-dose range, there really were no biologically significant changes observed at all," Doerge says.
It was only when exposures were millions of times higher than what people typically get that the scientists saw changes like those caused by the body's own sex hormones.
To double-check the results, the scientists also looked at how BPA was interacting with estrogen receptors — the part of a cell that usually responds to estrogen. And once again it was only the highest doses that produced interactions.
The results bolster previous studies by government researchers showing that people's exposure to BPA is lower than previously estimated and that the human body is really good at inactivating and eliminating BPA. But they are at odds with some smaller and less rigorous academic studies.
Some of the academic scientists who did those studies have already called the new government study flawed. They say it failed to look at things like brain development. They also say the results were compromised because even the "control" animals in the study had trace amounts of BPA in their bodies.
That sort of response is pretty typical in the debate over BPA and other hormonelike chemicals known as endocrine disruptors, says David Ropeik, a Harvard instructor and author of the book How Risky is it, Really? "The endocrine disruption issue has evoked some of the most visceral and ugly attacks among scientists of any scientific issue recently," he says.
For example, when the European Food Safety Authority concluded a few weeks ago that BPA is far less risky than some advocacy groups had suggested, "the endocrine disruption movement said, 'Oh my God, they're all corrupt. They're all taking corporate money,' " Ropeik says.
Lively debate is a natural part of science playing out in the public realm. But this sort of allegation may help undermine trust in regulatory agencies and their scientists, Ropeik says.
And it may leave consumers perplexed about what chemicals like BPA are actually doing in the body. In that case, Ropeik recommends referring back to the best science available.
Copyright 2014 NPR.