MONDAY, May 2, 2005 (HealthDay News) -- Even very low levels of a chemical found in plastic containers and tin cans boosts risks for prostate abnormalities in mice, and may do so in humans as well, researchers report.
They say fetal blood levels of bisphenol A "far below" thresholds deemed safe by the U.S. Environmental Protection Agency are associated with malformations in the prostates of developing mice -- malformations that could predispose these mice to cancer as adults.
"We've got to be concerned about exposure to this amount of bisphenol A, an amount that's actually below the EPA level. In fact, if you have a baby today, your baby is going to have more bisphenol A than levels used in this study," said senior researcher Fred vom Saal, a professor of biology at the University of Missouri.
In addition to helping lead this study, vom Saal presented data earlier this year to a special legislative committee in California that was considering the passage of a state bill banning bisphenol A in all products used by children aged 3 and under, such as baby bottles and plastic toys. The committee has since passed the bill, which is slated for a vote in the state's Legislature, he said.
According to vom Saal, bisphenol A is used to form a type of long-chain chemical used in great quantities by the plastics industry and in tin cans over the past 30 or 40 years.
"This chemical is inherently unstable, however, particularly if it's heated or there's any kind of alkaline or acidic contact," he said.
"What's interesting about bisphenol A is that it was also developed many years ago as a synthetic estrogen," added lead researcher Barry Timms, a professor of biomedical sciences at the University of South Dakota School of Medicine.
In fact, this same molecule is a key ingredient in many oral contraceptives, he said, creating another potential source for fetal exposure in women who may not realize they are pregnant and continue to take the Pill.
Diethylstilbestrol (DES), an estrogenic compound very similar in structure to bisphenol A, has long been connected to increased risks for uterine and other reproductive-tract cancers in young women, the researchers said. Timms said he and vom Saal "also started realizing that very small physiologic levels of these synthetic estrogens had an impact on prostate development," so they decided to take a closer look at bisphenol A.
In their study, which was published Monday in the online edition of the Proceedings of the National Academy of Sciences, the researchers fed pregnant mice doses of bisphenol A "below the range of exposure [found in] pregnant women."
They report that male mouse fetuses obtained from these pregnant mice showed significant malformations of the urethra, as well as abnormally large prostate ducts. According to Timms, bisphenol A appears to overstimulate certain prostate cells, increasing cell growth.
That could mean that, even at these very low exposures, newborn mice "will end up with larger prostates when they age than their [unexposed] counterparts," Timms said.
But while enlarged prostate is a relatively benign condition, prostate cancer is not, vom Saal noted.
"All these female sex hormones do the same thing -- they elevate receptors, priming the response system to male hormones in the prostate," he said. "So what you have is an organ that's hypersensitive to male sex hormones, and that's a risk factor for prostate cancer." In fact, therapies that suppress male hormones are a first-line treatment for prostate cancer patients.
Steve Hentges, executive director of the Polycarbonate Business Unit at the American Plastics Council, which represents the industry, said the study has a few important flaws.
First of all, he said, vom Saal's and Timms' characterization of the dosage the mice received as very low is "factually incorrect."
"The one dose that was tested in this study was 10 micrograms per kilogram of body weight," Hentges said. He added that a recent federal study measuring levels of bisphenol A in human urine found that "actual human exposure is down in the range of 20-30 nanograms per kilograms -- that's almost 1,000 times lower than what was tested in this study."
Hentges also contended that the mouse model used in the study "hasn't been validated as being relevant for human health," and said that malformations observed in exposed fetal mice may not be relevant to their health as adults.
Timms agreed that the dose used in the study was higher than that measured by the investigators for the U.S. Centers for Disease Control and Prevention. But he said "it's still much lower than the 'safe' level that has been determined for humans by the EPA. So irrespective of that, we're still seeing an effect at what we consider a very low level -- that's why we deliberately chose that dose range."
Based on this study and previous findings, vom Saal believes initiatives such as the California bill should be replicated in the other 49 states.
"The scientific community isn't debating this anymore," he said.
The Missouri expert stressed he's not advocating an industry-wide ban on bisphenol A, which previous animal studies have also linked to neuro-developmental problems, lowered age for puberty, and increased risks for breast cancer and polycystic ovary disease.
"I don't mind it being used in airplane wings and computers, things like that," he said. "But the idea that we need this in food storage items -- we just don't. We certainly don't need it in baby bottles, there are alternatives like polyethylene, polypropylene, glass."
One big problem is that it's tough right now for consumers to detect which plastics contain bisphenol A, and which don't, he added.
"Bisphenol A is typically in the clear, hard plastic," vom Saal said, "not the softer, non-clear containers. But until there's a right-to-know law, where the kind of labeling we have on food is demanded to be put on these products, you can't tell safe from dangerous plastic."
In the meantime, Americans -- especially pregnant women and those caring for small children -- might want to take some simple precautions, Timms said.
When it comes to plastics, tin cans and oral contraceptives containing this chemical, "the warning would be 'be careful, be aware,' " Timms said. "There are alternatives; you do have a choice."
For more on prenatal care, visit the March of Dimes.