WEDNESDAY, Aug. 15 (HealthDay News) -- A mysterious epidemic of thyroid disease in pet cats in the United States may be due to dust from fire-retardant chemicals used in carpets, furniture, mattresses, electronic products and even pet food, researchers report.

And while the researchers said there's no evidence to suggest a threat to humans posed by the chemicals -- called polybrominated diphenyl ethers (PBDEs) -- they can't rule out the possibility.

"Cats are very highly exposed to these chemicals, and the levels in cats are higher than the levels in people," said researcher Linda S. Birnbaum, director of the Experimental Toxicology Division at the U.S. Environmental Protection Agency. "But cats may be a good indicator of indoor exposure to humans," she added.

Symptoms of hyperthyroidism in cats include weight loss, increased appetite, hair loss and irritability. Hyperthyroid cats could serve as modern-day versions of the canaries in coal mines that alerted miners to poisonous gas, said Birnbaum, who added that hyperthyroidism is treatable in cats as well as people.

Feline hyperthyroidism is one of the most common and deadly diseases in older cats, and indoor pets are thought to be at greatest risk, Birnbaum said. Because of their conscientious grooming, cats ingest large amounts of house dust containing PBDEs.

Concerns about health effects from PDBEs began in the late 1990s, and studies have found that the chemicals cause liver and nerve toxicity in animals. "In addition, a recent study found an association with house dust and the levels of PDBEs in breast milk in women," Birnbaum said.

Many PBDEs, such as penta, which was used in polyurethane foam for furniture cushions and pillows, have been phased out either voluntarily by manufacturers or by bans from states and the U.S. government and governments overseas.

Despite these bans, BBDEs are environmentally persistent compounds, so it will take a long time before they disappear from the environment, Birnbaum said.

She noted that the EPA is looking for safer alternatives to some of the chemicals that will be fire resistant but not pose a potential health threat to animals or humans. So far, 14 alternative flame retardants have been evaluated, and furniture foam manufacturers are using new alternatives, according to the EPA.

In the new study, published in the Aug. 15 online issue of Environmental Science & Technology, Birnbaum and her colleagues took blood samples from 23 cats, 11 of which suffered from hyperthyroidism. They found that the cats with the disease had levels of PDBEs that were three times higher than younger cats and cats without the condition.

PBDEs are also found in canned cat food, particularly in fish/seafood flavors, such as salmon and whitefish. An analysis showed that diets based on canned food could have PBDE levels 12 times higher than dry-food diets. For these reasons, cats could be receiving as much as 100 times greater dietary PBDE exposure than American adults, the researchers said.

The danger of feline hyperthyroidism might be higher in the United States, where people have the highest reported PBDE levels worldwide, according to the report. In addition, by the late 1990s, North America accounted for almost half of the worldwide demand for PBDEs for commercial materials such as furniture and upholstery.

The epidemic of hyperthyroidism in cats began almost 30 years ago, experts say, at the same time that PBDEs were introduced into household materials for fire-prevention. Now the disease has been seen in Canada, Australia, Japan and many parts of Europe.

Hyperthyroidism has also increased in people. For example, former President George H.W. Bush and First Lady Barbara Bush have the condition, as does Millie, their Springer Spaniel.

More information

For more information on PBDEs, visit the Washington State Department on Ecology.

SOURCES: Linda S, Birnbaum, Ph.D., director, Experimental Toxicology Division, U.S. Environmental Protection Agency, Research Triangle Park, N.C.; Aug. 15, 2007, Environmental Science & Technology, online

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