TABLE 1.

Risk factors for feline hyperthyroidism identified in case-control studies

Study location	Numbers of cases (controls)	Study dates	Diet studied	Reported risk factors
New York State College of Veterinary Medicine, USA 19	56 (117)	1982–85	Diet for past 5 years	Non-Siamese breed. >50% canned food. Partial or complete indoor housing. Exposure to lawn or flea control products
University of California, Davis and Animal Medical Center, New York, USA 20	379 (351)	1996	Current and one previous diet	Non-Siamese or Himalayan breeds. >50% canned food. Exposure to cat litter
Seattle, WA, USA 21	100 (163)	1996–97	Diet for past 5 years	Increasing age. Preference for certain canned food flavors
New Zealand 22	125 (250)	1996–98	Current diet∗	Increasing age. Female sex. Domestic shorthair. Canned food of multiple flavors. Sleeping on the floor. Contact with flea and fly control products. Drinking puddle water and exposure to organic fertilizers
Purdue University, IN, USA 9,23,24	109 (173)	1998–200	Lifetime diet until 1 year before presentation	Increasing age. Female sex. >50% canned food. Food from pop-top cans. Baby food in regular kitten diet or as a treat. Lack of iodine supplement in label ingredients. Increasing frequency of carpet cleaning. Increasing years of exposure to well water. Increasing years of exposure to gas fireplaces
Hong Kong 8	12 (293)	2006–07	Not stated	Increasing age. Non-domestic shorthair breed
United Kingdom 25	109 (196)	2006–07	Diet for past 5 years	Increasing age. Non-purebred. Litter box use. >50% wet (canned/pouched) food. Canned foods. Fish in diet. Lack of deworming medication

^∗This was not explicitly reported but apparent from the context