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06/09/2008

Plastic bottles impair with memory and learning

Bisphenol A may impair learning and memory

Published on 05-09-2008 Email To Friend Print Version
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Exposure to bisphenol A, the hormonally active chemical used to make the linings of most tin cans and hard plastic bottles, may be able to alter brain function, impairing the ability to learn and remember, according to a new study by researchers from Canada and the United States.

The study, conducted on monkeys, whose brain development is similar to that of humans, raises the possibility that ailments such as depression, Alzheimer's disease and schizophrenia may be linked to the controversial chemical.

Almost all people living in industrialized societies are exposed to BPA as a result of trace amounts leaking from food and beverage containers.

The researchers, from the University of Guelph in Ontario and Yale University in Connecticut, found that low-level exposure to bisphenol A, or BPA, was able to block the formation of some types of synapses in the brain, the tissue that allows brain cells known as neurons to communicate with each other. The proper development of these synapses is considered crucial for remembering thoughts and experiences, and impairments in them are common in sufferers of depression and other brain-related ailments.

The study, to be published this week in the Proceedings of the National Academy of Sciences, is a significant advance over previous rodent-based findings that BPA is able to impair synapses. That research was open to criticism that what happened in the brains of a mouse or a rat was of limited applicability to the more complex brains of humans.

"If bisphenol A at these kind of low doses is able to interfere with [monkey synapses] then there has to be concern that continuous exposure to bisphenol A is probably not a good thing," said Neil MacLusky, a biomedical science professor at the University of Guelph and one of the study authors.

The researchers were able to cause the harmful effects with a daily dose of 50 micrograms per kilogram of body weight - the human-exposure limit currently considered safe by the U.S. Environmental Protection Agency. (A microgram is one millionth of a gram.) Although Health Canada's limit is half that of the EPA, Dr. MacLusky said standards in both countries are too lax and should be reduced.

"If we're getting a complete blockage of the effect" at the U.S. standard, then Canada's standard "is probably not safe," he said, although he cautioned that the doses used in his experiment were much higher than the exposure people would get from food and beverage containers.

Steve Hentges, a spokesman for the American Chemistry Council, which represents BPA manufacturers, criticized the study, saying it isn't applicable to people because the monkeys were exposed to the chemical through injection, while most human exposure is through diet.

Bisphenol A is mired in controversy because the manmade chemical is able to mimic the hormone estrogen in living things, and has been found in dozens of laboratory animal and test tube experiments to be biologically active at small doses. Although estrogen is most often viewed as the primary female sex hormone, it is also needed to ensure the proper development of synapses.

In April, Health Canada proposed adding BPA to Canada's list of toxic substances, which would make the country the first in the world to take such regulatory action.

Health Canada also said it planned to ban its use in baby bottles and have the infant formula industry cut the amount leaking from cans into baby food, based on concerns that current infant exposure didn't provide enough of a safety margin.

In response, most major retailers removed plastic water and baby bottles made with BPA from their shelves.

About three billion kilograms of BPA are produced each year, making it one of the highest volume synthetic chemicals.

A public comment period on Health Canada's proposals ended in June and the government expects to issue a final decision on its proposals on or before Oct. 18.

The new study by the Canadian-U.S. team is one of a growing number of scientific findings raising questions about the chemical.

Last month, researchers at the University of Cincinnati linked BPA to heart attacks and adult onset diabetes through its ability to suppress the production in human fat tissue of a key hormone that protects people against these conditions.

The National Toxicology Program, part of the U.S. Department of Health and Human Services, issued a report yesterday on BPA that raised concerns the chemical may be able to alter the prostate gland and the brain, and cause behavioural changes, particularly in cases of exposure during fetal development and childhood.

"There remains considerable uncertainty whether the changes seen in the animal studies are directly applicable to humans, and whether they would result in clear, adverse health effects," said John Bucher, associate director of the National Toxicology Program, in a statement. "But we have concluded that the possibility that BPA may affect human development cannot be dismissed."

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