Published by: Ingrid King. Last Updated on: June 28, 2023 by Crystal Uys

bowl of wet food on the floor near cat looking up

Hyperthyroidism is a common disease that typically affects middle-aged and older cats.  It is caused by an excess production of thyroid hormones, which are produced by the thyroid gland, located inside the cat’s neck.  Thyroid hormones affect nearly all organs, which is why thyroid disease can sometimes cause secondary problems such as hypertension, heart and kidney disease. There has been much speculation about what causes hyperthyrodism in cats. One of the culprits may be your cat’s food.

University of Georgia study looks at whether cat food ingredients play a role in disease development

Researchers at the University of Georgia are examining whether cat food ingredients play a role in disease development. In a study funded by the Morris Animal Foundation, researchers treated feline thyroid cell cultures with various cat food ingredients to determine whether these ingredients stimulate normal thyroid cells. From the foundation website:

Researchers learned that flavonoids—plant proteins found in commercially available cat food—activate cultured feline thyroid cells as effectively as a cat’s normal thyroid-stimulating hormone. This suggests that flavonoids may interfere with normal thyroid function and be a contributing factor in the development of feline hyperthyroidism. Researchers have to confirm these results by repeating the necessary experiments. Final analysis and results are expected by summer 2013.

If the researchers identify nutritional causes of hyperthyroidism, it is hoped that these compounds can be reduced or avoided in cat food, thus reducing the incidence of disease and improving the lives of cats.

Editor’s note: Soy is a common source of flavanoids, and is also a common ingredient in lesser quality pet foods. Soy protein is cheaper than meat protein, which is why manufacturers often use it to boost the protein content in pet foods. Unfortunately, cats lack the enzyme to properly metabolize plant-based proteins.

domestic tabby cat looks at a bowl of food that the owner is holding in his hand
Image Credit: Valeri Vatel, Shutterstock

Is there a relationship between canned foods and an increase in feline hyperthyrodism?

In a 2004 study at Purdue University, researchers investigated the medical records of 169,576 cats, including 3,570 cats with hyperthyroidism, evaluated at 9 veterinary school hospitals during a 20-year period. The study concluded that the increasing prevalence of feline  hyperthyroidism is not solely the result of aging of the cat population, and that canned foods may play a role.

A much smaller 2000 EPA study of 100 cats with hyperthyroidism and 163 control cats identified a chemical called bisphenol-A (BPA) which is used to coat the inside of cat food cans, as a possible culprit. Interestingly, cats in the study that preferred fish or liver and giblets flavors of canned cat food had an increased risk.

What role do PBDE’s play?

Another chemical that may play a role in the increase in hyperthyroidism may be polybrominated diphenyl ethers (PBDEs). PBDEs are flame retardants used in building materials, furniture, carpeting, and textiles. Intestingly, PBDEs are also found in particularly high concentrations in fish that are high up the food chain, such as tuna and mackerel, two fish proteins widely used in fish flavored cat food.

What do these findings mean to you and your cat?

Clearly, more research is needed to definitively identify a connection between feline hyperthyroidism and cat food, but the research that has been done so far is enough to convince me to err on the side of caution when it comes to choosing cat food. Avoid foods containing soy protein, make sure the brand you feed uses BPA-free cans, and limit fish flavored foods to an occasional treat.

Man shopping in supermarket reading cat food label product information
Image Credit: LADO, Shutterstock

Featured Image Credit: Nils Jacobi, Shutterstock

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