A chemical used in everything from food-can linings to store receipts might also pose some risk for infertility and birth defects, a new study suggests.
Exposure to bisphenol A, or BPA, may disrupt the human reproductive process and play a role in about 20 percent of unexplained infertility, said researchers from Harvard University.
In laboratory experiments, they exposed 352 eggs from 121 consenting patients at a fertility clinic to varying levels of BPA.
"Exposure of eggs to BPA decreased the percentage of eggs that matured and increased the percentage of eggs that degenerated," said lead researcher Catherine Racowsky, director of the assisted reproductive technologies laboratory at Brigham and Women's Hospital in Boston.
BPA also increased the number of eggs that underwent an abnormal process called "spontaneous activation" that makes eggs act as if they have been fertilized when in fact they haven't been, Racowsky said.
Moreover, many eggs exposed to BPA that matured did so abnormally, increasing the odds for infertility and birth defects such as Down syndrome, she said.
Eggs exposed to the highest levels of BPA were the most likely to show these ill effects, the researchers found. Their results are similar to earlier research examining the effect of BPA on animal eggs, they said.
Racowsky cautioned that these latest results with human eggs were seen in the laboratory, so whether BPA exposure works the same way in real life isn't known. And the research also found only an association between BPA and infertility and birth defects, not necessarily a cause-and-effect link.
In addition, the eggs used in the experiment were going to be discarded because they didn't respond normally and thus could be considered damaged to begin with, she said.
BPA is known to disrupt the hormonal system, with the chemical acting like an artificial estrogen. "There are many ways it can disrupt the hormonal system," Racowsky said.
The chemical is all throughout the environment, Racowsky said, and it's almost impossible to avoid exposure to it. "People need to be aware of the toxins in the environment and try to lead the healthiest life they can possibly lead," she said.
The report was published online July 31 in the journal Human Reproduction.
Dr. Avner Hershlag, chief of the Center for Human Reproduction at North Shore University Hospital in Manhasset, N.Y., agreed that a laboratory finding does not necessarily mean the same effect will be seen in the real world.
"When you make a leap from the lab to patients you have to examine a whole different model," said Hershlag, who was not involved with the study. "To say from [the results] that this might explain part of unexplained infertility is a bit of a stretch. Unexplained infertility remains unexplained."
One industry group concurred, pointing out that real-world settings often do not mirror lab experiments.
"The physiological relevance of this study is entirely unclear since the BPA concentrations showing effects are vastly higher than the concentration of BPA that could be present in the human body," said Steve Hentges, of the Polycarbonate/BPA Global Group of the American Chemistry Council.
Hentges added that numerous animal studies, "consistently have concluded that BPA does not affect fertility or other reproductive parameters at any dose even remotely close to human exposure levels."
Hershlag also noted that the plastic equipment used with in vitro fertilization (IVF) may contain BPA and could affect the ability of eggs to mature, so it might be better to use glass. That, he suggested, might even improve the success of IVF.
The U.S. Food and Drug Administration has banned the use of BPA in products such as baby bottles and sippy cups, but the chemical continues to be used in many other consumer products.
The most prominent continuing use of BPA is in the lining of aluminum and tin cans, where it prevents corrosion.
BPA also is found in inkless cash register receipts, which are coated with the chemical, and a study has shown increased BPA levels in the urine of people who have touched a receipt.