VOA标准英语2013--Common Chemical May Damage Teeth（在线收听）

Common Chemical May Damage Teeth

A chemical compound that’s been linked to a number of health problems in animal studies may also damage tooth enamel in humans. BPA is found in many resins and plastics that people use everyday, such as water and baby bottles and food containers.

BPA, or Bisphenol A, can leach from the plastic and into food, water or snacks – and from there into us. A U.S. Centers for Disease Control survey in 2003/2004 found detectable levels of the chemical in 93 percent of more than 2,500 urine samples tested. It can also contaminate the environment, with countless plastic bottles littering many landscapes and waterways.

The NIH, the National Institutes of Health, says, “Animal studies indicate BPA may cause adverse effects, such as obesity, behavioral changes, diabetes, early onset puberty, asthma, cardiovascular diseases, reproductive disorders and development of prostate, breast and uterine cancer.”

It adds there is “reason for concern, especially for parents, because some animal studies report effects in fetuses and newborns exposed to BPA.” There’s ongoing research on whether BPA does indeed affect people the way it can animals.

French researcher Sylvie Babajko is the lead author of an article on BPA appearing in the American Journal of Pathology. She said that BPA is an endocrine disruptor.

“An endocrine disruptor is a substance that disturbs the endocrine system. That means hormones in humans, as well as in progeny.”

The endocrine system is a series of glands, such as the thyroid pituitary and adrenal, which release hormones affecting sexual development, growth and metabolism. And these hormones go everywhere in the body. Some chemicals can make their levels go up and down.

Babajko and fellow researchers are now trying to confirm that BPA can damage tooth enamel. She said they were notified about the possible link by others studying the effects of endocrine disruptors on lab animals’ reproductive systems.

“They found that the rats exposed to low doses of endocrine disruptors presented white spots on incisors. They called us and we studied these white spots and found that there was an enamel hypomineralization due to endocrine disruptors exposure,” she said.

In other words, BPA, circulating in the body, can adversely affect cells that produce tooth enamel, making it fragile or brittle. The question is: Are those white marks now showing up on human teeth as well?

“It is probably a problem,” she said, “because things and food contain BPA and we are probably all exposed to BPA. And it has been shown, at least with experiments on animals, that BPA can cause a lot of defects and teeth are one additional target of BPA.”

Analysis of the rats’ teeth show similar characteristics found in about 18 percent of children between the ages six and eight. These kids may have teeth that are extra sensitive to pain or more liable to get cavities. It’s believed humans are most sensitive to BPA in the first years of life. Further study is needed, but those white streaks may be an indication of early exposure to the chemical.

Since BPA can disrupt estrogen levels in animals, there’s concern that could affect men’s reproductive health. Men do produce estrogen, but usually in much lower levels than women. However, Babajko said that’s not been confirmed and is difficult to prove.

“It is possible, but not demonstrated in humans, of course, because we are all subjected to many endocrine disruptors. And it is difficult to be sure that BPA is the only one that is responsible for the reproductive defects. It is difficult to know precisely if BPA is the only one or if it is acting in combination with other molecules,” she said.

Concerns about BPA have led to the production of BPA-free plastic products. Europe banned baby bottles containing the chemical in January 2011. The U.S. took similar action in July of last year. While the Food and Drug Administration began voicing concerns about BPA in 2010, it has not officially reversed its 2008 decision declaring BPA safe.

France intends to extend the BPA ban to all food containers in July 2015.