Consider this: Of the more than 100 independently funded experiments on BPA, about 90% have found evidence of adverse health effects at levels similar to human exposure. On the other hand, every single industry-funded study ever conducted -- 14 in all -- has found no such effects.
Surely you've heard about BPA by now. It's everywhere. Some 7 billion pounds of it were produced in 2007. It's in adhesives, dental fillings, and the linings of food and drink cans. It's a building block for polycarbonate, a near-shatterproof plastic used in cell phones, computers, eyeglasses, drinking bottles, medical devices, and CDs and DVDs. It's also in infant-formula cans and many clear plastic baby bottles. Studies have shown that it can leach into food and drink, especially when containers are heated or damaged. More than 90% of Americans have some in their bodies.
BPA is dangerous to human health. Or it is not. That's according to two government reports in recent months that came to opposite conclusions. The National Toxicology Program (NTP), which is part of the National Institutes of Health, reported in September 2008 "some concern" that BPA harms the human brain and reproductive system, especially in babies and fetuses. Yet less than a month earlier, the U.S. Food and Drug Administration declared that "at current levels of exposure" BPA is safe. Even after the FDA's own science board questioned the rigor of this analysis in late October, the agency didn't change its position.
Let's take a moment to ponder this absurd dichotomy. How could our nation's health watchdogs reach such divergent conclusions? Are we being unnecessarily scared by the NTP? Or could the FDA be sugarcoating things? What exactly is going on?
What is in dispute is whether the tiny doses of BPA we're exposed to are enough to trigger such hormonal effects. For decades, the assumption was that they didn't. This was based on traditional toxicology, which holds that "the dose makes the poison." In other words, a threshold exists below which a compound is harmless. This makes intuitive sense. Consider alcohol: The more you drink, the drunker you get; but if you drink just a little -- below the threshold -- you may not feel anything. In the 1970s and 1980s, government scientists used standard toxicology to test BPA. They concluded that, at doses far higher than those found in humans, it may cause organ failure, leukemia, and severe weight loss. Yet as BPA products have made their way into every part of our lives, biologists have discovered evidence that very low doses may have a completely different set of effects -- on the endocrine system, which influences human development, metabolism, and behavior.
At first, these discoveries emerged by accident, when test tubes and petri dishes in laboratories were switched from glass to plastic. A group of Stanford researchers in 1993 found that breast-cancer cells it was studying reacted with a mysterious estrogen, which it traced to polycarbonate lab flasks. A few years later, Patricia Hunt, a geneticist at Case Western Reserve University, discovered abnormalities in the chromosomes of her lab mice. She eventually concluded that damaged polycarbonate cages were at fault.
In 1995, a developmental biologist named Frederick vom Saal stepped into the picture. A tenured professor at the University of Missouri -- Columbia, with funding from the National Institutes of Health, vom Saal tested BPA to see how it interacted with samples of human blood. He found that, because it bypassed mechanisms that control the dose of hormones in the body, its estrogenic effects were magnified. "We said, 'Wow, that's bad. This stuff should be considered a lot more potent than it is,' " vom Saal recalls. He then fed small amounts of BPA -- 25,000 times lower than the EPA's toxic threshold -- to pregnant mice. He discovered that the compound enlarged the prostates of the male offspring, signaling potentially serious developmental disorders. His study was published in 1997 in the peer-reviewed journal Environmental Health Perspectives.
In the years since, more than 100 experiments have shown BPA to cause permanent harm in lab animals at the low exposure levels found in humans.
