An epidemic of thyroid disease among pet cats could be caused by toxic flame retardants that are widely found in household dust and some pet food, government scientists reported Wednesday.
The often-lethal disease was rare in cats until the 1980s, when it began appearing widely, particularly in California cats. That was at the same time industry started using large volumes of brominated flame retardants in consumer products, including furniture cushions, electronics, mattresses and carpet padding.
Scientists from the Environmental Protection Agency noted a possible connection between hyperthyroidism and flame retardants. The chemicals -- known as polybrominated diphenyl ethers, or PBDEs -- mimic thyroid hormones, so experts have theorized that high exposure in cats could cause overactive thyroids.
Cats that remain indoors and eat fish-flavored canned food were found to be the most highly contaminated.
"We know there is an association between indoor living for cats and hyperthyroidism," said Linda Birnbaum, a senior author of the study and the EPA's director of experimental toxicology. "Our paper does show cats are highly exposed and hyperthyroidism may be due to the high PBDEs. More studies are needed to fully determine this."
A major unanswered question is whether cats are the proverbial canaries in the coal mine, signaling health dangers for their owners. Cats and human beings are the only mammals with a high rate of hyperthyroidism.
So far, no link has been established between human endocrine disorders and exposure to flame retardants. However, "there is growing concern," the scientists wrote.
"It is clear that house cats may be able to serve as sentinels for indoor exposure to PBDEs for humans who share their houses," said Birnbaum, one of the world's leading experts on hormone-altering chemicals.
Brominated flame retardants are ubiquitous outdoors and inside homes. The chemicals have been building up in people and wildlife over the last two decades, particularly in the United States, where human concentrations have doubled every few years.
People in the United States have the highest PBDE levels in humans worldwide, but U.S. cats are even more exposed -- some with levels 100 times greater, according to the study.
Twenty-three cats were tested in the EPA's study, including 11 with hyperthyroidism. The researchers found that the cats with hyperthyroidism had substantially higher levels of a PBDE compound. Symptoms of the disease, which is a leading cause of cat death, include weight loss, rapid heartbeat and irritability.
