I’ve written before about how hyperthyroidism is of special concern to me since I saw an 80% rate of the disease in my previous generation of cats, much higher than the “over 10%” prevalence rate in the general population. When new research came out last week about a potential link between hyperthyroidism and cat food ingredients, it really caught my attention.
Setting the Stage: What is Hyperthyroidism?
Hyperthyroidism is a hormonal disorder in cats where the cat’s thyroid gland 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 there is no definitive answer to the question of what causes it in cats.
Previous Theories about Feline Hyperthyroidism Causes
In the past, a few strong theories about what causes feline hyperthyroidism have been discussed in scientific literature.
BPA
One theory was that hyperthyroidism was caused by the chemical bisphenol A (BPA). As with human canned foods and beverages, BPA was added as a lining to the inside of cat pop top lids to prevent corrosion and extend shelf life. The chemical then absorbed into the food in the container, which was of eaten by cats.
A study showed that cats eating canned food with pop top lids were at a higher risk of developing hyperthyroidism. The study itself didn’t implicate BPA, but at the time, BPA was used to line cat food pop top lids. BPA has been found to be a thyroid receptor agonist, which could lead to hyperthyroidism. The pet food industry has since phased out BPA from lining can lids.
Flame Retardants
Another theory was that flame retardants used in household goods leach out of our sofas, carpets, and plastics and combine with household dust to deposit in a cat’s fur. Those chemicals are then ingested during grooming.
A study in Sweden showed that cats with hyperthyroidism had elevated levels of polybrominated diphenyl ethers (PBDEs), which are flame retardants. PBDEs were removed from the market in the US in 2005, but household goods purchased before then would still contain them.
A New Theory: Fish Ingredients
A new study looks at PBDEs and polychlorinated biphenyls (PCBs) levels in both pets and pet foods. Like PBDEs, PCBs are now banned in the US due to a variety of health impacts including disrupting thyroid hormone levels.
Researchers noted that both environmental pollutants also have been seen in fish, which is a common ingredient in commercial cat food recipes. They tested levels of both chemicals levels in dog and cat foods. They found that PCB levels are significantly higher in cat food than in dog food and that levels were higher in kibble than in canned foods. Fish is a more common ingredient in cat than dog food, and canned foods with fish were higher in PBDEs. In fact, in the study, “chicken and tuna” food for cats had higher PBDE levels than “chicken and tuna” food for dogs.
The researchers did blood tests on cats who ate the foods and found that cats retain a much larger load of byproducts from PCBs and PBDEs than dogs. They pointed out that hyperthyroidism in dogs is very rare, and that a cat having a much lower capacity to metabolize chemicals that are common in fish may be a reason that we see a higher number of cases of hyperthyroidism in cats.
What this Means for Cat Food Consumers
As anyone who has already tried to limit fish in their cat’s diet because of allergies or out of concerns about mercury, phosphorous, or magnesium levels can tell you, it’s hard to do. Fish is found in more foods than you expect, and the labeling requirements for cat food allow it to be used in recipes that don’t include it in the product name. It isn’t unusual to read the ingredient panel of “chicken entree” and discover it also contains fish. This is especially true of bargain-priced foods.
Additionally, cats are often seen as convenience pets, and they are frequently fed dry food because that’s convenient, too. The concerns raised in this study about the thyroid-disrupting chemicals being much higher in dry foods are one more argument against the popular kibble diets.
My previous generation of cats were fed primarily kibble, and I wasn’t much of a label reader for much of their lives, so it’s likely they ate more fish than I realized. Perhaps this contributed to the higher-than-average hyperthyroidism level I saw in my household. I’ll never know for sure, but anything I can do to keep from having to face giving pills to the three worst pill-taking cats in the world is something I’ll keep in mind whenever I feed them.
Research and further reading:
Journal of the American Veterinary Association, Epidemiologic study of relationships between consumption of commercial canned food and risk of hyperthyroidism in cats
Endocrinology, Bisphenol-A, an environmental contaminant that acts as a thyroid hormone receptor antagonist in vitro, increases serum thyroxine, and alters RC3/neurogranin expression in the developing rat brain. http://www.ncbi.nlm.nih.gov/pubmed/15498886
Environmental Science and Technology, Higher PBDE Serum Concentrations May Be Associated with Feline Hyperthyroidism in Swedish Cats
Environmental Health Perspectives, Blocking Brain Development, How PCBs Disrupt Thyroid Hormone
Environmental Science and Technology, Organohalogen Compounds in Pet Dog and Cat: Do Pets Biotransform Natural Brominated Products in Food to Harmful Hydroxlated Substances?
Photos courtesy
sorsillo on depositphotos
Autumn Barnes on flickr creative commons
RasulovS on depositphotos
Tom Woodward on flickr creative commons
Raven says
Very interesting information. Unfortunately, they may never determine the cause (or causes) since most pet cats’ lives are highly variable. The best we can do is try to avoid the things that may be problematic and hope we’re doing the right thing.
We were very lucky in that our one cat who developed hyperthyroidism loved getting his tapazole-cheese-ball twice daily! He didn’t mind his twice daily insulin injections either. But I would not want to tempt fate again and paws crossed Raven does not develop hyperthyroidism (or diabetes).
Summer says
My human has been avoiding cat food containing fish for a long time now! It’s not always possible – even premium poultry, lamb or rabbit-based cat foods sometimes reveal that they contain fish, once you read the ingredient list. But I’m pretty sure we eat a lot less fish than your average kitties!
Marg says
That is a very interesting report. Hyperthyroidism is not fun. But it sounds like it would be hard to not feed foods that don;t have fish in them. Great review.
The Island Cats says
We don’t get a lot of fish foods…but as Summer said, lots of foods that say they are poultry based still have some fish in them. We wish the manufacturers didn’t see the need to include it.
Rose the Kitten says
My Giant Lady, does not give us Cat food fish. Only chicken and Turkey.
When we do get fish, its her wild caught human tuna, even then, we only gets a little bite.
Luvs,
Rose ~ the adult Kitten
Random Felines says
that is very interesting….
Melissa & Mudpie says
I’ve only had one cat (so far) with hyperthyroidism and that’s when I became to the godsend known as compounded transdermal meds! I’m thankful Mudpie isn’t a fish fan at all 🙂
Annabelle says
That is very interesting development. Thank you so much for sharing this with all of us.
Andrea and the Celestial Kitties says
Wow, that’s interesting. We’ve been off fish for years here because it can also be a cause of crystal in urine and Leo had an issue. No problems since we removed fish from his diet. And yes, it’s hard to find fish free food. Some stuff that looked really good would have herring oil near the bottom of the list. Luckily we found stuff they like that is fish free, just a touch more expensive than we’d like but we do it anyway so we don’t have any problems.
If you think about it, cats are descended from desert animals, no fish in the desert.
Flynn says
That is interesting to know. Neither Eric nor Flynn would eat any fish menu cat food, however Flynn has developed a liking for Tuna in the last 18 months. This is since he was diagnosed with hyperthyroidism though. He also does eat some meals which come in a pop top can, but the majority comes in sachets. I think it is unlikely that he developed it through his diet, but of course cannot say for sure. I really believe that it could have been triggered, or more like accelerated by stress when Eric died.
Madi says
Ohhh thank you for all this very valuable information…..
I have my mini senior Physical tomorrow..since I’m almost 14 my vet has suggested a mid year blood panel just to check on things.
Hugs madi your bfff
Brian Frum says
That was an amazing and interesting bunch of information on hyperthyroidism! Well done!
da tabbies o trout towne says
uh……guys….thiz ree port doez knot bode well for uz….doez it ~~~~~~
🙁
yet on de other hand…it COULD meen mor…. pizza piez 🙂
thanx for sharin thiz info, we appreciatez it ♥♥♥
Jenna Meow says
We avoid fish for all the reasons above. I was the same as you, previous cats were fed cheap kibble because I didn’t know any better. Knowledge is power. Thanks for sharing!
Caren Gittleman says
Thanks for this info! I used to be upset that Cody HATES fish…(yep, he won’t touch fish!!) Now, I am happy about that!
Connie says
There is also the theory that cats who are fed foods that are high in parts of the animal that hold the thyroid gland have thyroid issues..
Annie says
Thanks for this post! I never fed fish foods until Annie joined our household more than four years ago now. She wouldn’t eat anything unless it was fish. Coincidentally, in just the last week or so, I’ve been thinking about making a strong effort to stop the fish food. I have a few cases still, but plan on just buying chicken (with no fish in the ingredient list). Now, thanks to this article, I have even more incentive.
The Florida Furkids says
Good info. We had no idea about the lining of cat food cans having BPA.
The Florida Furkids
Layla Morgan Wilde says
I wonder if they tested feral cats who live exclusively on fresh caught fish in harbors, have the same results. Thanks for mentioning BPA. As pollution increases, pet owner need to make more careful choices.
Mark's Mews says
We are glad we get mostly good-quality poultry-based Stinkey Goodness!
Ellen Pilch says
Excellent post. I never buy fish flavors, but I am not a label reader so the chicken and turkey I buy must have it which would explain why 3 of my 13 cats are hyperthyroid.
Cathy Keisha says
Nicky hated fish and died at 9 years old. Autumn and Faith ate lots of fish and lived into their mid teens. I could not live without fish. Just like the peeps said when they were told to limit their sweets, why live to be a ripe old age if you can’t enjoy anything you like. I’ll just cross my paws although I don’t eat those cheap store brands.
Fur Everywhere says
This is very interesting, and it kind of makes me glad that Carmine and Milita cannot eat fish. I was surprised when I first started reading cat food labels. It’s very common for companies to sneak fish into their beef recipes. I can’t feed Carmine and Lita many beef brands because it’s so common for them to put fish in these formulas.
Kitty Cat Chronicles says
Great and well-researched article. Very interesting too. Because of the other reasons you mentioned not to feed fish, my cats don’t eat any food that has fish listed as an ingredient, unless it’s in some treats that we won in a giveaway or someone gives us. Now I’m even more relieved to know my cats don’t eat any fish!
Christy Paws says
A very excellent post. Thanks for the info. Since mom makes us raw food, she knows exactly what’s in it. We get some sardines every once in a while and maybe a bite of mom’s salmon.
Maxwell, Faraday & Allie says
Fascinating! Another reason to avoid fish in foods.
Kitties Blue says
Our kitties eat a mix of kibble and canned, and a variety of “flavors” of canned food. Previous generations of our kitties have eaten only kibble. Of the eight current kitties and the nine angels, I have never had a cat with hyperthyroidism and some have lived to be quite old. I think everything in moderation is the best way to go. Hugs, Janet