Environmental Risk Factors for Feline Hyperthyroidism: Pet Cats as Potential Sentinels for Public Health

Edinboro C.H., Scott-Moncrieff J.C. and Glickman L.T.

Thyroid, 2004. 14: p.759.


Cats now live in approximately 34% of American households. With an average of two cats per home, this represents about 73 million cats that share the household environment with humans. Since it was first described in 1979, the incidence of clinical hyperthyroidism in cats has risen at an epidemic rate to become the most commonly diagnosed endocrine disease in older cats. The specific etiology is unknown, but it is most probably multifactorial in nature, involving host (age, gender, breed), environmental, and nutritional factors. Clinical hy- perthyroidism in cats resembles toxic nodular goiter in humans, a disease of the elderly seen more often in iodine-deficient areas. In two earlier epidemiologic studies of feline hyperthyroidism, an association was found with exposure to lawn chemicals and treatment with flea control products. In our recent case-control study of feline lifetime nutrition and health, we found that female cats were twice as likely as males to develop hyperthyroidism. Here we report that significant environmental risk factors for hyperthyroidism varied by sex. After adjusting for age, hyperthyroidism among male cats was associated with each additional year of well water consumption (odds ratio [OR] = 1.11, 95% confidence interval [CI] = 1.02, 1.21) and each additional year of exposure to gas fireplaces (OR = 1.26, 95% CI = 1.03, 1.54). For female cats, the association was with carpet cleaning more than twice per year (OR = 6.98, 95% CI = 1.20, 40.55). Most of these risk factors are or contain goitrogenic substances found in the households shared by humans and cats. The remaining associations should be examined in greater detail to determine their applicability to human health. Thus, cats as companion animals may be sentinels of public health issues.