Hyperthyroidism in cats is not caused by cans, according to Dr. Michael Fox's Q-and-A column in the Pocono Record.
Some cat owners believe the condition is caused by the plastic lining in cans of wet cat food and that cats fed only dry food cannot be affected; however there are no reports in veterinary literature that prove this, according to Dr. Fox. The only known problem of endocrine-disrupting chemicals on the inner lining of cans is bisphenol-A (BPA), but other sources of chemicals can cause even more harm. These sources include dioxins and PCBs found in animal fat and bromides used in fire-retardant chemicals. Bromides can be found in the dust on carpets and upholstery in most homes, as well as in seafood. Petfood manufacturers are phasing out the use of cans lined with the epoxy compound containing BPA.