Four of the five cats in my previous generation of cats suffered from hyperthyroidism.
They weren’t all related to each other. Louie and Talia were siblings, as were Rhett and Radcliffe, but the siblings pairs weren’t related to each other, or to Cyrano. Knowing that, I always have felt like it must be a very prevalent disease rather than something that just ran in the family. I was surprised to learn that while hyperthyroidism is seen in over ten percent of senior cats. The 80% rate of the disorder among my cats significantly overrepresented the norm! It made me wonder why.
What is Hyperthyroidism?
Hyperthyroidism is a hormonal disorder in cats where the cat’s thyroid hormone overproduces the thyroid hormones. Elevated thyroid hormones can cause weight loss, hyperactivity, vomiting, and even aggression. In humans, hyperthyroidism is linked to Grave’s disease and iodine insufficiency, but it is unknown what causes hyperthyroidism in cats.
The fact that feline hyperthyroidism was first seen in the 1970s and is has grown exponentially since then correlates to the use of flame retardants in household items, especially plastics and fabrics used for furniture. It is possible that the flame retardant leaches out of the materials over time and combines with dust to deposit in a cat’s fur, which they then ingest when grooming.
A recent study of cats in Sweden found that those with hyperthyroidism had elevated levels of the flame retardants known polybrominated diphenyl ethers (PBDEs). The study was not broad enough to prove that the chemicals caused the disorder, but it did show that cats suffering from it have it in their systems, meaning it could be linked to hyperthyriodism.
The study analyzed blood samples from cats with both hyperthyroidism and normal thyroid function. Cats with elevated thyroid function had elevated levels of PBDEs. All of the cat blood samples also contained another flame retardant, BB-209. BB-209 was discontinued in 2000 and PBDEs were removed from the market in the US in 2005, yet many households still have items that were purchased before then.
Links at Home?
While this study couldn’t conclusively identify PBDEs as a cause of hyperthyroidism, the results lead to wonder about to the high incidence of hyperthyroidism in my house. I would love to see this studied on a much wider scale and see if other variables make a difference. My cats were indoor cats. Did that lead them to even more exposure to PBDEs from furniture and carpets than cats who roam outside? Is there any way to avoid these chemicals when they are used to treat so many household items where cats walk, sleep, and play?
The EPA has an action plan to make rules and encourage voluntary phase-out of manufacture and support of these chemicals. Perhaps when PBDEs are removed from the market, the number of hyperthyroidism cases will drop, too. That remains to be soon. For now, I’m glad to be living in a house without carpeting. It seems like a safer option until veterinary science understands more about why cats in my house over-represent this disease.
Update: New research is available. Don’t miss reading Feline Hyperthyroidism Linked to Fish in Cat Food.
References and further reading:
Environmental Science & Technology, Higher PBDE Serum Concentrations May Be Associated with Feline Hyperthyroidism in Swedish Cats.
Journal of Feline Medicine and Surgery, Hyperthyroidism in cats: what’s causing this epidemic of thyroid disease and can we prevent it?
Environmental Protection Agency, Polybrominated Diphenyl Ethers (PBDEs) Action Plan Summary