Published by: Ingrid King. Last Updated on: February 1, 2023 by Crystal Uys


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.

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.

Photo Credit: Kevin N. Murphy, Flickr Creative Commons

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49 Comments on Feline Hyperthyroidism and Cat Food: Exploring a Possible Connection

  1. Yes… I believe that all the food has too much iodine and kelp in it and that is what’s causing hyperthyroid in cats

  2. My cat Rudy has thyroid problems.the vet said get thr hills cat food.can I boil organic chicken for him
    And can I give him are fresh liver once a week
    And where do I get raw cat food

    • I’m assuming the Hill’s diet your vet recommended is the y/d diet, here’s more information:

      Organic chicken and fresh liver is not a complete and balanced diet. You can get commercially prepared raw diets at most pet stores. You can find our recommendations here: or you can make your own properly formulated raw diet, here’s more information:

      You will still need to treat the thyroid issue with either medication or the I-131 treatment. Here’s a comprehensive article about feline thyroid disease:

  3. One of my girls has been diagnosed with hyperthyroidism a few years ago. Although her T4 levels were slightly above the range, the vet put her on a low dose of Tapazole (gel). Maybe we caught it early? Nevertheless, I’m trying to eliminate fish from their diets (i just recently discovered that fish contributes to hyperthyroidism) and researching new wet food. But it looks like all of them contain some form of iodine – in order to meet AAFCO “balanced diet” standards, i guess. The most popular are iodine, calcium iodate, potassium iodide, and kelp (sometimes, both ingredients are used, like in Ziwipeak – kelp AND calcium iodate). My question is how dangerous it is for hyperthyroid cats? To my understanding, there’s no such wet food with low iodine levels (I’m not even considering feeding my cats Hill’s “prescription” junk). But I’d rather feed my kitty a quality ingredients balanced diet with standard levels of iodine than low-level iodine low-level quality “prescription” garbage. Are the levels of these iodine supplements something to be concerned about? Is one preferable over the others (natural, better-digestible, etc.)?? Any other recommendations? Thanks.

    • I don’t think anyone has established “safe” iodine levels for hyperthyroid cats. You probably already came across this article by Dr. Mark Peterson during your research, it’s a few years old but probably still accurate:

  4. In my experience with cats of which I’ve had many, the only cats of mine that ever got hyperthyroidism were the ones who ate dry food not canned.

    Now that I only feed canned or raw food my cats have never been healthier. I even cured cat’s of obesity, diabetes and a food allergies because many dry foods use a flavoring spray that is addictive to some cats and dry foods contain too many carbs as our cats are obligate carnivores. This causes overeating and obesity and disease.

    The best info on diet for our obligate carnivores diets can be found right here:

    • Did the dry food contain kelp or potassium iodide or any other source of iodine? Just curious…I’m exploring a new theory…

    • Re dry food – you are partially correct. According to one of many studies quoted in the incredibly comprehensive blog – felinecrf (dot) org, dry food is more likely to do damage to cats BUT the canned food and recently highlighted problems with food with fish and BPA liners plus sub-par ingredients resulted in nearly four times the number of thyroid problems. I just replied to a Marie above and unfortunately know the topic too well. My 17 year old boy has thyroid disease and renal as well. I basically brought him back from the dead, pushed back on the knee jerk reaction from the vet to simply up his thyroid med (which in days nearly killed him) and found a way to nourish him with even better food, no dry and added more healthy fat than even before. Still – dry is not good. Wet, however, is not better and can lead to a hell of a lot of problems. Tanya’s Renal blog is also a wealth of info. Glad that Jennifer in Aug 10 ’13 brought up potassium iodide. That is problematic. In fact – a traditional vet may often suggest that a thyroid cat has to switch to the (hills, may be?) lowest iodide food or whatever that next prescription food is. PUSH BACK IMMEDIATELY. Once your cat begins to eat this it can NEVER eat anything else. NEVER. It is one of the latest additions to the suite of prescription foods and is an absolute travesty. My almost dead pet is now thriving on frozen and rehydrated raw, gets extra raw protein (not less), he gets extra enzymes, two doses of Aventi (for renal support w/vit B), pollock or wild salmon oil (Grizzly brand) and a 40K capsule of serrapeptase at least once a day. No fish, no cans, no grains, no soy. He’s 17 now and I almost lost him six months ago. Now, I expect a couple of more years at this rate. If I only knew then what I know now.

      • You are correct about BPA also being implicated in thyroid disease. Many premium cat food manufacturers now use BPA-free brands. Unfortunately, this is not usually disclosed on the label, so you’ll have to contact the manufacturer to find out.

        And I completely agree with you on the Hill’s y/d prescription diet. Here’s my take on it:

      • hey Victoria, I was just wondering how your kitty was doing on is diet? I was also wondering how you make his food and with what ingredients. My 16 year old cat was just diagnosed with hyperthyroid and I’m thinking of switching over to a raw diet but don’t know how or what to give for a healthy diet for a hyperthyroid kitty. Any info would be greatly appreciated! Thanks!

    • Keli, my cat Armand is 12 and now he has it and never ever has he eaten dry kibble. I have been supplementing with raw chicken and turkey. There is a conspiracy going on in this country to keep us and our pets sick whether you believe it or not. The drug corporations and the food ones own our government. We pay more for health care than any other country and have the worst health. We are all low in iodine because they replaced it with bromine in the bread in the 70’s. Look that bromine up – it’s just lush. Look at how much iodine the Japanese consume daily and then compare it to our RIA and look at their incidences of say breast cancer. I am going to find an Holistic vet and Dr. for me.

      • Working with a holistic veterinarian who understand both conventional and alternative medicine gives you the best of both worlds.

  5. It’s just so confusing these days! My Kasha will be turning 16 July 1st and was diagnosed with Hyperthyroidism in January.(I also have it, which is ironic) I give her the Med’s she needs twice a day and is doing well. Thank goodness it was caught before it caused more problems.
    I also have 2 rescues and 1 stray and I’m lost with all the different information. One rescue only eats Fancy Feast Flaked Tuna and Shrimp maybe 1/2 ounce everyday, but she refuses to eat anything else, trust me I’ve tried them all one at a time. They are all on Grain Free dry food and all get wet food twice a day. I’ve done so much reading that my mind is spinning.
    I think as being Loving Cat Caretakers we always feel guilty if something happens with our Babies and most of the time it’s out of our control.
    So I keep straining my eyes hoping someday I’ll find the truth!

    • You’re right, most of us always feel like we’re not doing enough, and we somehow should have known better.

  6. I am the mom of 5 cats. My 15 year old Tabitha was diagnosed with hyperthyroidism about 8 years ago. In December ’12, we were told she was in kidney failure and said she may have 6 months; less if she didn’t eat. She is on medication. She is still with us. It’s very difficult to get her to eat. I have 4 other cats that I want to feed good, quality food. If I can prevent or reduce the chances of them getting it, that would be great. One of my 5 is a rescue, Tigger. At 8 months old he was diagnosed with feline leukemia. He stays separate from the other cats. He is 5 years old TODAY!!! He will only eat friskies indoor delights. Believe me I’ve tried everything I know to switch him to a higher quality food. I don’t have children. These cats are my children. So the more information I can get to help my children would be fantastic.

    • Marie, if you look around the Feline Nutrition section on this site, you’ll find lots of information on how to transition cats to a healthier diet.

    • Marie, if you are still checking back about this I have things to share with you which might be of help here. If your pets who are refusing to eat do not have diabetes, consider looking into Aventi. It is designed for cats with renal disease BUT many cats treated for thyroid problems often discover that the excessive metabolism hid other issues like renal disease. Many are elder and stop eating. Cats need vitamin B and many do NOT get enough through food. It helps them get their appetites back. The other thing is slippery elm bark slurry but I’ve had such good outcome with Aventi that I will continue to add that to my ‘kid’s’ rehydrated raw food. I also make a wholesome bone broth (from non-hormonal chickens – see Dr Karen Becker’s instructions on line if not sure) and he really enjoys drinking it. Here is our story – My 17 year old boy was diagnosed with hyper thyroid disease about a year ago. He might have had it for up to a year longer but we blamed other issues on his renal disease. He was put on the regular meds (2.5 mg metamizole once daily). We went on for some time but his weight continued to drop along with his appetite – anorexia is often a side effect of the med and older cats not only need x2 more nutrition than a cat but more fat. Most vets (traditional ones) want to reduce protein but it’s all about cooked not raw. Many new studies now have shown just how wrong that path of thought is. There is another piece to that puzzle – he has renal disease since 2009 when bacteria from his mouth traveled to his kidneys and we almost lost him. This also gave him a stage 1-2 heart murmur. So now a cat of 11 lbs gradually got to 9, then 8 and then barely 6.5. My vets suggested increasing his thyroid meds to help him retain weight and tried to force him into eating his prescription lower fat food (expensive, he hated it). W/in the week as I weighted him in early Oct ’13 as we waited for the last round of blood tests – he was barely aware of his surroundings, stopped eating, was shutting down. I swore not to drag out his suffering for my sake, found a wealth of information on vitamin deficiency and co-existing conditions on www felinecrf org i.e. Tanya’s renal log (IT IS AMAZING), found Aventi powder and started to add to his food – it’s inexpensive on Amazon. IT WORKS! The other brand available has to be refrigirated and fed unbroken in a pill. Good luck with that plus it’s expensive to buy and ship. I also went all raw, returned to his original med amount, removed all canned and fish-flavored food from his diet, boiled broth and gradually saw him – each day, grow more aware and functional. When we did blood tests again his vet commented that he gained two lbs, his renal reading got better (!) and thyroid stayed where it was. The big change was Aventi – it has extra vitamin B with enzymes which neutralize the bad stuff in the kidneys and help flush it out. Yes, there is a diuretic and the cat does pee but it flushes out the stuff you don’t want. It’s flavorless but there is some sweetener of sorts that is not good for diabetic cats. It is not uncommon for hyperthyroid cats to get a renal failure or issues once on meds – it’s not because of the med, but rather – once thyroid is a bit under control it exposes other problems by slowing down. At any rate – I hope this helps. If I had a cat w/o renal issues I would still sprinkle some of the stuff on or at the very least give it a bit extra vitamin B. I promise the appetites will go up. Good luck to you!

      • Thank you for sharing your experience in such detail, Victoria -and thank you for not giving up on your kitty! I was not familiar with Aventi, but will definitely take a closer look at it!

      • Hi Victoria and Ingrid,

        Was wondering Victoria what kind of all raw diet you feed your cat. Because all I can find is raw food with kelp and iodate forms added. Also, what kind of rehydrated raw food do you feed your Cat? Again, I am only finding rehydrated foods that contain kelp. My cat of 15 years was diagnosed with hyperthyroid and trying to find the best diet for her health. Even the honest kitchen prow has potassium iodate in the food. Please Victoria or Ingrid if you of any frozen or rehydrated raw food that contains no iodate or kelp please let me know. Thank You all for posting and Ingrid for having such a Awesome Blog!!! Sincerely,

        Mercedes(cat/child) and Tonya(mommy)

  7. My 18 year old Maine Coon has been fighting this disease since he turned 10. I could not afford irradiation therapy so he had surgery and one of his tyroids were removed. He was fine for 5 years. They told me he was at high risk for a re occurrence of the disease. So now I have a dermagel pen and put the meds on the inside of his ears every day. His cat food has always been dry Hills Science. Then the last 3 years he could not digest dry food anymore so I switched him to Fancy Feast Appetizers, chicken ( a fairly pure protein in a plastic container). We supplement with a vet specialized dry food for his digestion problems. I don’t think anything but nature going array caused his health problems. But this was interesting reading.

  8. My cat was recently diagnosed with diabetes. I was told by the vet and thru online info that it was caused by the food and all the junk in it. There really should be more controls on people and pet food in this country. There are so many chemicals and altered products in the things we eat. I too have many medical problems due to the food I used to eat. What can we do about this?

  9. My 14 y.o. cat was recently diagnosed with hyperthyroidism and related heart murmur. He has been raw fed for most of his life, and all of the last ten years, or so. His raw foods did not include any fish. There are no guarantees that raw feeding prevents disease, and that includes dental problems. Many people make this sort of statement, and I myself have been one of them in the past. I know better now, unfortunately.

  10. I have a genetic disposition for a low thyroid. Could cats also be genetically more likely to have a problem with their thyroid as well? Personally, I think the chemicals put into food for a longer shelf life is harmful for everyone, including our pets. Nothing should last for a few years. I know that I have noticed how chocolate has a waxy flavor now that was not there when I was a child. I wish we could go back in time and get rid of this idea of a long shelf life. I would rather shop more often than eat chemicals mother nature never intended us to eat. And that goes for my cat as well.

    • I’m sure genetics play a role, too, Lisa, as do the chemicals in our food and in our environment. I agree that we would all be healthier if we had fewer toxic substances in our, and our pets’, lives.

  11. Our mom is jumping up & down, pumping her hand in the air, yelling YESSS! (we think she kind of LOVES this article…)

  12. Thank you for posting this. I still wonder if/how I contributed to my mackerel tabby Wellington’s hyperthyroidism. He was diagnosed at about age 9 and died at 14 from congestive heart failure; the enlarged heart was a direct result of the thyroid condition.

  13. Read “Foods Pets Die For” by Ann N Martin. It will open your eyes.

    Cats are ‘true carnivores’ and they are being given a highly processed, cooked diet loaded with additives, chemicals, and inappropriate base ingredients.

    Cats should eat healthy dead animals. Dead animals are a complete, wholesome, appropriate diet for cats.

    But seriously; read that book. The pet food industry will horrify you, shock you, and blow your mind.

    *disclaimer* I do not have any gain by recommending the above mentioned book. I am a dog lover, and want to see America wake up.

    • I agree totally! I have no idea why snakes are fed mice and rats, but cats are not. Cat food should consist of whole mice and small birds. (my apologies to those with mice and birds as pets…it’s a messed up world)

  14. another nail in the coffin of ‘lets feed plants to carnivores”.. first they lack the digestive enzymes to properly break down plant based ingredients, now there is evidence it is actually harmful.. Thank you for sharing!!

  15. My cat was hyper-t at 7 years old and I was really shocked because he had been eating wellness grain free canned for at least 2 years prior to the diagnosis. I wrote to the company in 2009 to validate that there was no BPA used in the cans and they confirmed. I did however, feed the formulas that included fish and since I live in california all furniture, beds etc have to contain fireproof materials which are also suspected to play a role in developing this condition. He is on commercial raw food now and thankfully is euthyroid at this time.
    This is an all too common feline disease that is difficult to avoid even in the most health conscious households!

    • You’re right, Barb – we can’t avoid all hazards, but we can do the best we know how to by educating ourselves.

    • OMG. I posted above before I read your post. My cat has been eating the same Wellness grain free canned food for several years. She will turn 7 in November. She’s having hyperthyroid symptoms and her TT4 was inside the gray zone and the vet thinks she may be hyperthyroid or will be down the line. This is too much of a coincidence. Maybe it’s not the BPA at all. Maybe it’s the potassium iodide. I recently had been giving my cat a supplement called Nupro Health Nuggets for cats which bragged about containing kelp and lots of iodine….well my cat was worse while I was giving her the nuggets as far as hypterT symptoms. She improved when I stopped giving her the nuggets. Hmmmmm. Iodine.

    • Hi barb, Great to hear you cat is now euthyroid!!!!!!!!!!!!!! What type of commercial raw food are you feeding your cat? My Cat was diagnosed with hyperthyroid and trying to find a healthy diet for her. Most of the raw food I have come across had kelp or some form of iodate. Any answer would be greatly appreciated!!!!

  16. I would love to hear more about cat and cancer. My 13 year old cat died and vet said it was Meow Mix cat food because of food dyes.

    • I’m so sorry about your kitty, Vona. I don’t think there’s ever one single cause for cancer, but foods containing artificial ingredients and dyes certainly could be a contributing factor.

  17. Fascinating post, Ingrid. Thank you. Which cat food brands do not have BPA in the cans, do you know?

    • I’m pretty sure that none of the brands that I recommend have BPA in their cans, Anjali. Click through on the link in the sidebar for a full list.

      • ” link in the sidebar for a full list.” and which of the bazillion links on the sidebar would you be referring to? I linked this on a blog and we all have the same question. I’d love to be able to post a link.

  18. All of this is very interesting for me since Jackie had hyper thyroidism at age 7. The thought that the cat food might have caused her illness just makes me sick and mad.We are sure glad to have Jackie with us still.

    Mary Beth, Tom, and the fur kids who love their canned food now.

    • That’s an awfully young age to be diagnosed with hyperthyroidism, Mary Beth. The more we can find out about what causes it, the better we can prevent future cats from getting this disease, Mary Beth. While I doubt that all pet food manufacturers will make changes to their products, there are brands out there that don’t use flavanoids or BPA’s.

    • My cat is 6 1/2 (will turn 7 in Nov.) and she is having hyperthyroidism symptoms. Her TT4 was just inside the “gray zone” and the vet thinks she may be hyperthyroid. I have been feeding her canned food and kibble soaked in water for years and now I’m wondering if I should only feed her kibble and quit the canned food altogether. The companies say the cans are supposed to be free of BPA and the foods have little or no fish ingredients which I read are also a suspect in hyperthyroidism. But, still, I’m with you…if the food I am giving her is to blame…it just makes me want to cry. I also give her home grown wheat grass everyday for the vitamins and fiber. She loves veggies like lettuce and romaine. They probably have some bioflavanoids in them. I wonder if that could be to blame….? I hate the not knowing. It makes no sense that the more effort I put into her diet to make it healthy, the more it could be making her hyperthyroid.

      • Jennifer, I think you can make yourself crazy trying to figure this one out! 🙂 All we can do is the best we know based on the research we’ve done when it comes to feeding our cats. That’s interesting about the kelp supplement – I suppose it’s possible that it pushed her into hyperthyroidism, especially if she was already predisposed to it.

    • I am so glad that you still have your fur baby, we lost my Newton Kitty at 12 from this disease. I started researching things and at least his loss helped save the rest of my fur babies. It took a lot of trial and error to find the grain free food that they liked and would eat, but they are all worth it

      • Hi Wendy,
        What kind of grain free food are you feeding your cats? My cat 15 years diagnosed with hyperthyroid about a month ago. she has eaten dry food all her life. Switching too wet food slowly at the moment. However, need help with finding cat foods that contain no kelp, iodates, or iodine of any kind. Really want to give her the raw food but don’t know any without kelp. Thank You so much for this blog!!! Please help!!!

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