Research overview: environmental hypotheses for feline hyperthyroidism

The apparent emergence and rise of feline hyperthyroidism since around 1980 has prompted investigation of environmental risk factors, including flame-retardant chemicals such as polybrominated diphenyl ethers (PBDEs) found in household dust and some cat foods, as well as dietary iodine variability and goitrogenic compounds. Cats, with their grooming behavior and indoor lifestyles, may have distinctive exposure patterns. This overview synthesizes the epidemiologic and toxicologic literature rather than one citation, describing the leading environmental and dietary hypotheses, why establishing causation has been difficult, and how studies of these exposures attempt to explain a disease that seemed to arise in modern times. It matters because identifying modifiable causes could enable prevention of a now-common and burdensome disease of older cats.