A study, performed at the Royal Veterinary College, London, UK concluded that there is a decreased risk of hyperthyroidism in Tonkinese, Abyssinian, British Shorthair, Burmese, Siamese and Persian cats (Himalayans?). The study was first published: 13 June 2017.
You can see that some of the breeds are pointed cats. It had been thought, therefore, that cats with a pointed coat may have a decreased risk of contracting hyperthyroidism. I think that the argument was that a relatively greater amount of tyrosine is made available for thyroid hormone production in these cats.
Tyrosine is an amino acid. It is associated with the creation of melanin pigment at the extremities and is an essential precursor of thyroid hormone.
The argument is that a temperature-sensitive mutation in the tyrosinase gene prevents tyrosine from converting to melanin except at the cat’s extremities which are cooler. This leaves more tyrosine available for thyroid hormone production. This then protects against the development of hyperthyroidism.
You can read the full report on the study on the Wiley Online Library.
Hyperthyroidism is common in older cats (at 20% of the population in the study). The study also found that there was no connection between the cat’s coat and hyperthyroidism in non-purebred cats. This would seem to undermine the study’s findings. Hyperthyroidism is a multifactorial condition by which is meant that the causes are complex.
It was also concluded that cats with long hair were at a higher risk than cats with short hair. Female cats were at a higher risk than male cats. Neutered cats had a higher risk than intact cats. Cats in the age range 11 to 17 were at a higher risk for hyperthyroidism then were 10-year-old cats.