What causes feline hyperthyroidism?

According to one study over 10% of senior cats suffer from hyperthyroidism (12.3% in felines> 8 years old) (Kohler et al 2016). This means over 1 in 10 elderly cats in a standard population will develop the condition.

However, it is unclear exactly what causes these hormone-producing nodules to occur in the first place.

This condition seems to have become more commonly recognised in recent years, leading some people to think that perhaps a modern change in our pet’s environments could be responsible.

Studies have looked at chemicals, including those used in fire retardant coatings on furniture, and at canned wet cat food, particularly fish or liver flavours. Studies have also explored cats that are kept primarily indoors and those that have regular exposure to flea sprays, fertilizers, pesticides, or insecticides.

As there is currently no proven link or cause between any of these factors, there is nothing that you could have done to prevent this condition from occurring. (Vaske 2014). The fact we are routinely blood testing cats more often may also be part of the reason why we are diagnosing more cases.

However, we do know there are certain risk factors which increase your cat’s chances of developing the condition which include –

Age – Older cats are more likely to develop hyperthyroidism, with cases highest between 14 and 17 years of age (Stephens et al., 2014).

Breed – non-pure breed cats are more likely to develop the condition than pedigree cats

Sex – both males and females can develop the condition, but females are slightly more likely

The exact patient numbers can be seen in this table from a recent study (Stephens et al., 2014).