By Amanda Gardner
WEDNESDAY, June 10 (HealthDay News) -- More potentially harmful health effects have been discovered for the chemical bisphenol A, found in clear plastic bottles and other everyday items, according to several new animal studies.
Not only are humans probably being exposed to generally unsafe levels of BPA, as the chemical is commonly called, but it could be causing arrhythmias, or irregular heartbeats, research shows. That could be especially problematic for women, who may be at higher risk for this type of cardiac threat.
In addition, other researchers say that they have found the mechanism by which BPA, a synthetic hormone with estrogen-like properties, might affect later fertility of babies whose mothers were exposed to the chemical.
These findings are being reported this week at the Endocrine Society's annual meeting, in Washington, D.C.
BPA, a chemical used to harden plastics, is in myriad items, including CDs, sunglasses and dental sealants. It is also in the lining of metal cans and bottle tops. Some studies have linked it to cancer, diabetes, heart disease and developmental problems in children. Health advocates say exposure to the chemical could present a particular problem to developing fetuses.
The U.S. Food and Drug Administration agreed in early June to reconsider its position that BPA is safe at levels found in baby bottles and other common products.
Researchers for one of the studies to be presented this week concluded that estrogen and BPA cause heartbeat irregularities in heart cells isolated from rats and mice.
"Basically, it's very clear that BPA is acting like estrogen," said study co-author Scott Belcher, an associate professor of pharmacology at the University of Cincinnati. "If we give estrogen at physiological concentrations, then add BPA, it's actually a synergistic effect. It's not like adding the two together. It's worse."
Women are more likely to die after a heart attack than men, and Belcher suspects an increased rate of arrhythmia might bear some of the responsibility for that trend.
His team is currently collecting human heart cells from transplant patients to try to replicate the findings.
In another study, researchers report on the mechanism by which BPA affects fertility in the offspring of rodents.
"The genes that are necessary for normal pregnancy are altered," explained study author Dr. Hugh Taylor, director of the division of reproductive endocrinology at Yale University School of Medicine. "It changes the DNA code and the ability of DNA to express these genes."
"A little transient exposure during a brief time period in pregnancy could permanently alter the DNA of the uterus," Taylor added.
For pregnant women, the message is "just try avoiding drinking out of hard water bottles and eating out of cans and perhaps not getting expensive dental work with sealants," Taylor said. "There's nothing wrong with eating fresh vegetables."
In a third study, researchers warned that people may be getting higher-than-recommended exposure to BPA from both known and unknown sources, a conclusion they drew from research involving monkeys. The researchers, from the University of Missouri, had compared the blood level of BPA in monkeys given high doses of the chemical with average levels found in people in the United States and other developed countries.
More than 8 billion pounds of BPA are used in the manufacturing of products each year, they said.
Chemical industry representatives, however, disagree that the findings represent any real threat to human health.
"It is disappointing to see that researchers continue to inject animals with bisphenol A since studies of this type have recently been acknowledged by the National Institute of Environmental Health Sciences to have limited impact on our ability to assess human health effects," said Steve Hentges, executive director of the Polycarbonate/BPA Global Group at the American Chemistry Council.
"Most notably though, a study on rhesus monkeys appears to confirm that bisphenol A is efficiently converted after oral exposure to biologically inactive metabolites, which are then rapidly eliminated from the body without bioaccumulation," Hentges added. "This data supports the conclusions of many government bodies worldwide that bisphenol A is not a significant health concern."