Dr. Miaomiao Wang, of the California Environmental Protection Agency has published a study of older cats in Northern California that suggested a link between higher levels of per and polyfluoroalkyl (PFAS) substances in cats with hyperthyroidism.
PFAS is found in chemicals that are used in industrial processes and consumer products. These chemicals are found in many household products such protective coatings for carpets, furniture and apparel, paper coatings, and insecticide formulations, just to name a few products.
More research is needed but it is a good idea to keep this in mind. If there are health issues from this chemical in cats, we have to suspect dogs as well. Dogs are more likely to chew these products than cats are.