Feline Hyperthyroidism Update

Discovery News reported this week that “In a new study that analyzed the blood of 62 domestic cats and 10 feral cats, researchers from the University of Illinois at Urbana-Champaign found that cats living inside homes had higher blood levels of a class of chemicals called PBDEs, compared with their outdoor-living peers.”

Unfortunately, that is not news; that study was originally published in 2009. (Read it here: www.istc.illinois.edu/info/library_docs/RR/RR-115.pdf). That study wasn’t terribly original even then; it’s based on Dr. Larry Glickman’s work at Purdue from 2004.

There are more than 200 different PBDEs, which are relatives of PCBs, although only 9 are of great concern. They are found at different levels in different animals and tissues. These chemicals can disperse far from their sources, and they are strongly persistent in the environment. Even wild animals are contaminated. Fatty animals like ducks have fairly high levels, while pheasants have much less. In animals raised for food, not even organic or vegetarian-fed animals are exempt.

While much of the research has focused on canned cat foods, the issue may actually be what’s in those cans: the ocean is loaded with PBDEs, and foods containing fish also contain high levels of PBDEs. Chickens, too, contain varying amounts of PBDEs. Because the liver is the body’s main detoxifier, this may account for the finding that PBDEs are higher in foods containing “by-products,” which often include liver. PBDEs bio-accumulate in fat, which is higher in whole chicken than in chicken meat, and higher still in l0w-ash chicken by-products, a common cat food ingredient. PBDEs are also high in farmed fish–the source of most salmon used in cat food–probably because there are high levels found in in fish food. Oddly, turkeys are higher in PBDEs; turkey products are included in “poultry by-products.” Dry pet foods also contain PDBEs, but they apparently contain a different set of them than canned cat foods.

California, where the first cases of feline hyperthyroidism occurred, banned PBDEs in 2003. The EU banned them in 2004. The U.S. stopped manufacturing the worst ones in 2004. Levels of PDBEs in food animals have decreased by about 60% since then. However, the incidence of hyperthyroidism in cats has not decreased, suggesting that food is not the major issue. Scientists speculate that there may be other routes of exposure for meat animals, and hence, for cats; most likely dust and other environmental factors.

For more information, see our article on Feline Hyperthyroidism, or watch a video interview with Dr. Jean here:

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