Here is an interesting article I came across in the New York Times Magazine regarding feline hyperthyroidism. ~ Amy Johnstone, DVM

“Forty years ago, feline hyperthyroidism
was virtually nonexistent. Now it’s an
epidemic — and some scientists think a class
of everyday chemicals might be to blame.”

https://www.nytimes.com/2017/05/16/magazine/the-mystery-of-the-wasting-house-cats.html