Like lead before the 1980s, Bisphenol-A (BPA) is everywhere. BPA is the main building block of polycarbonate plastic, a highly useful hard plastic found in a wide variety of products, such as eye glass lenses, consumer electronics, medical equipment, and bicycle helmets. It’s also found in the lining of metal food and beverage containers, and it’s used to synthesize hard plastic kitchen utensils, food storage containers, baby bottles, and water bottles.
It’s the intersection of BPA with food and beverages that has some researchers concerned. That’s because small amounts of BPA from plastics and linings can leach into our food and drinks. The problem: BPA isn’t just a building block of plastic—it’s also a weak estrogen that acts as an endocrine disruptor in the body.
Like lead, BPA poses particular risks for infants and children. In addition, maternal exposure to BPA can also impact the developing fetus. Those exposed to even low levels of BPA before reaching sexual maturity may experience structural problems with their reproductive organs, infertility, and an increased rate of reproductive cancers like breast and prostate cancer later in life.
Can Plastic Really Be Dangerous?
In November 2006, 38 of the country’s leading BPA researchers gathered to collectively review the copious literature that has been published on BPA. The panel specifically examined the impact of the low-level BPA exposures that are found in most people in the United States.
The panel concluded that there is sufficient evidence from animal and molecular studies to link low-level exposure to BPA with a variety of problems and expressed “great cause for concern” about the potential for similar problems in humans. The problems they identified included reproductive tract abnormalities, increases in reproductive cancers, decreased semen quality, early onset puberty in girls, and insulin-resistant diabetes.
Exposure to environmental estrogens like BPA early in development can permanently alter the way certain organs develop and can create a predisposition for cancer later in life. Most vulnerable are the reproductive organs, which are rich in estrogen receptors. This is not just true for females, but also for males.
“Although estrogen is thought of as a female hormone, it’s found in both males and females, and the prostate gland is rich in estrogen receptors,” says Gail Prins, Professor of Physiology at the University of Illinois at Chicago. “There are also estrogen receptors in other parts of the body, including the cardiovascular system and the brain. That’s why estrogen-mimics like BPA can influence both the reproductive tract and other parts of the body as well.
In addition to binding to estrogen receptors, BPA can also create problems by permanently altering the epigenetic programming of the cells, thereby creating permanent defects in how a person’s genes work.
“If you think of our genes as computer hardware, the epigenome is the software that tells the gene what to do,” says Randy Jirtle, Professor of Radiation Oncology and an epigenetic researcher at Duke University. “BPA can create bugs in the software. Then every time you copy the program, you copy the buggy error into another cell. If those errors get introduced early in development, all of the cells that are later generated have the same problem.”
Epigenetic changes caused by BPA not only cause problems for the exposed individual, they can also be passed on to future generations if they occur in the sperm or egg.
Evidence of Problems in Humans?
“We’ve done this experiment on humans before,” says Patricia Hunt, a geneticist at Washington State University, “only we ran it with diethylstilbestrol (DES) instead of BPA.”
Like BPA, DES is a synthetic estrogen. In fact, DES was discovered in the late 1930s, just a few years after scientists had begun exploring using BPA as an estrogen substitute for women. Scientists chose DES instead of BPA, and by the late 1940s, DES was prescribed for a number of problems, including preventing miscarriages.
Decades later, doctors discovered a rare form of vaginal cancer in girls whose mothers had taken DES while pregnant. Eventually it was found that more than 90 percent of DES daughters (those exposed to DES in utero) have abnormalities of the reproductive tract, says Retha Newbold, a reproductive and developmental biologist for the National Institute of Environmental Health Sciences, which is part of the NIH.
While the rates of problems aren’t reported to be nearly as high in DES sons, Newbold notes that some did suffer from reproductive tract abnormalities, including retained testes that had to be surgically corrected.
Once the problems with DES were discovered, researchers began studying its effects on mice and rats. The conclusion: the problems found in humans also occurred in lab animals.
The animal research also suggested that fetal exposure to DES may be correlated with hormone-sensitive cancers (such as breast and prostate cancer) later in life. As the early DES daughters approach middle age, there are indications that they are at higher risk for breast cancer as well, says Dr. Ana Soto, a professor at Tufts University School of Medicine.
After more than a decade of research on the effects of BPA, scientists are finding that the same patterns of problems associated with DES in animals and humans are also found in animals exposed to BPA.
This gives Soto reason for concern: “It would take several decades to study the correlation between prenatal exposure to BPA in humans and potentially increased rates of reproductive cancers later in life. Do we want to wait another 50 years to see what happens with BPA?”
June 21st, 2008 |