Flame retardant found in upholstered furniture may cause hyperthyroidism in cats
Feline hyperthyroidism was first diagnosed in cats in 1979. One year later, in 1980, 1 in 200 cats were diagnosed with feline hyperthyroidism. Today, an estimated 1 in 10 cats are affected.
Feline hyperthyroidism is the most common endocrine-related disease of older cats, and while the actual cause of feline hyperthyroidism is unknown, scientists have long speculated that it could be environmental—indoor cats and cats who have regular exposure to flea sprays, fertilizers, pesticides, or insecticides have been found to have an increased incidence of hyperthyroidism—but a direct cause and effect has never been demonstrated.
Now, a new study by researchers at Oregon State University (OSU) may provide some answers.
Scientists previously suspected this dramatic increase in cases of feline hyperthyroidism could be linked to household flame retardants that were introduced in the mid-1970s. At this time, manufacturers began to put polybrominated diphenyl ethers (PBDEs) into textiles, polyurethane foam, plastics, and electronics.
But in 2004, US manufacturers started voluntarily phasing out these flame retardants amidst environmental and health concerns and promptly replaced them with a different class of chemicals: organophosphate esters such as tris(1,3-dichloroisopropyl) phosphate (TDCIPP). But recent research suggests these flame retardants, like PBDEs, can act as endocrine disruptors.
Could the new flame retardants that replaced PBDEs be causing this near epidemic of feline hyperthyroidism?
Kim A. Anderson, PhD, corresponding author of the article and environmental chemist in the OSU College of Agricultural Sciences, developed a silicone pet tag to test that theory. Silicone absorbs volatile and semi-volatile organic compounds, and silicone wristbands have been used in previous studies to check exposure to environmental chemicals in humans.
“The tags are porous and chemically very similar to human cells,” Anderson said. “Molecules of contaminants embed themselves in the silicone in the same way they’d go into the cells in your body. The silicone is a pretty good mimic of the types of chemicals that you can absorb—what we call passive sampling.”
Researchers attached the pet tags—similar in appearance to a rabies tag—to the collars of 78 hyperthyroid and non-hyperthyroid cats seven years and older. The cats wore the tags for seven days, after which their owners filled out a questionnaire. Once the tags were collected, the researchers extracted the chemicals they’d absorbed by soaking them in a solvent.
They found more than 20 individual flame retardants in at least one tag. But only levels of TDCIPP differed between tags worn by hyperthyroid and non-hyperthyroid cats.
They found higher levels of TDCIPP in the cats with hyperthyroidism. Higher TDCIPP exposures were found in cats exposed to air fresheners and in cats who prefer to nap on upholstered furniture.
Significantly, TDCIPP is still commonly used as a flame retardant in upholstered furniture and some gel air fresheners.
“The way a cat is diagnosed with feline hyperthyroidism is by extremely elevated concentrations of thyroid hormones,” Anderson said. “Seeing the correlation is suggestive of a connection between thyroid function and exposure to TDCIPP.”
Photo credit: iStock/Nils Jacobi