Food + Chemicals + Dust = Hyperthyroid Kitties?

A serious disease affecting cats’ thyroid glands has risen to epidemic proportions since the first cases were diagnosed in 1979. It is a worldwide phenomenon, though worse in the U.S. than other countries.

The disease itself, called hyperthyroidism (hyper = too much, thyroid = a hormone-making gland), is seen mostly in older cats age 10 or more. Thyroid hormone regulates the body’s basic metabolic rate. Too much of it is like drinking too much coffee—it speeds up every reaction in the body.

Symptoms of hyperthyroidism are related to excess thyroid hormone: excessive hunger, weight loss, restlessness, yowling, vomiting, diarrhea, and heart disease. However, about 20% of cats are “atypical” and do not show these symptoms. (Dogs also develop thyroid disease—but in the opposite direction. They are more prone to hypothyroidism; a deficiency of thyroid hormone.)

Many theories have been proposed to explain the dramatic rise in feline thyroid disease. Because it affects so many cats, the focus has been on widespread, environmental causes.

Studies have found several suspects in cat food:

  • One theory implicates the large excess of iodine found in many cat foods. Humans can develop hyperthyroid disease from too ingesting much iodine; might cats do the same? Iodine is difficult and expensive to test for; instead, pet food makers routinely add extra, just to make sure that minimums are met. But how much is too much? So far, nobody knows; and nobody is really looking.
  • Several studies found an increased likelihood of developing thyroid disease in cats who eat a lot of canned food. Specifically, they found a higher incidence of hyperthyroidism in cats that ate fish or “giblet” canned foods. “Giblet” is another name for organ meats commonly listed on pet food labels as “by-products.” Better-quality, natural cat foods do not contain by-products, although some include specific organ meats like liver.
  • Recent research suggests that the culprit may be a chemical (bisphenol A and similar compounds) found in can linings of pop-top cans that can leach out into the food and cause toxicity (the smaller the can, the more chemical exposure the food has). However, there are at least 25 different types of can linings, and the particular type used by a manufacture may change over time. It is difficult to know which foods may be affected, and to what degree. The FDA, however, has stated that the amount of chemicals that may leach into the food is unlikely to cause disease.

A new study that recently captured media attention suggests that fire-retardant chemicals known as PBDEs may be a factor in feline hyperthyroidism—even though the study itself clearly states “no association was detected between hyperthyroid cats and PBDE levels.” The authors note that PBDEs were introduced at about the same time hyperthyroidism was first described in cats. California was particularly aggressive in promoting these life-saving fabrics, which could explain why the veterinary school at U.C. Davis saw so many early cases of hyperthyroid disease in cats. Additionally, the rate of feline hyperthyroidism has roughly paralleled the use of PBDEs in other countries. This particular study looked at only 23 cats (less than half with hyperthyroid disease; and the case controls were not well-matched in age or gender.

The main route of exposure in cats was hypothesized to be the PBDEs contained in carpets, upholstery, and mattresses—and the dust mites that live in these fabrics. Electronic equipment, which attracts dust, is also a suspect. Since cats often sleep on carpets, sofas, chairs, mattresses, and nice warm TVs and stereos, their exposure could be high and prolonged. Subsequent grooming would then cause the cat to ingest a fairly large amount of dust. This may explain why hyperthyroidism is also more common in indoor cats.

Perhaps the most interesting wrinkle in this recent study is that PBDEs were also found in cat food. For two major types of PBDEs, high levels were found in canned food, especially fish- or seafood-based cat foods. However, high levels of other PBDEs were also found in dry cat food.

The double (or triple) whammy from PBDEs, can liner chemicals, and excess iodine may be too much for many cats to handle. However, outdoor cats who never eat canned food can also develop the disease—so other factors that haven’t yet been discovered are likely to be involved.

What can you do to minimize the risk for your cat? Well, it wouldn’t be smart to push your cat outdoors—the dangers outside are far worse, and most of them will kill your cat long before the age where she’s at risk for thyroid disease. Ripping out all your carpets and throwing away your furniture probably isn’t practical.

However, we also would not recommend feeding only dry food. There are many health risks for cats that eat too much dry food, including obesity, diabetes, arthritis, urinary tract disease, constipation, kidney disease, and inflammatory bowel disease. A variety of high-quality, natural foods—including at least 50% canned food—is your cat’s best bet for a long and healthy life.

4 thoughts on “Food + Chemicals + Dust = Hyperthyroid Kitties?

  1. My female cat (9 years old) has just been diagnosed with hyperthyroidism and we are beginning treatment. She has been eating dry and canned Wellness cat food for about a year and a half. My vet’s handout on the disease says that pop-top canned food may have triggered or accelerated the disease. Should I discontinue the Wellness canned food. I’m so confused as I thought I was doing the best for her with Wellness food.

    1. Excellent question! Most brands of canned cat food use pop-tops for the majority of their foods. There are dozens of types of can liners, and unfortunately, there’s really no way to know which is which.

      The study did not say which brands of cat food were tested. However, it’s a pretty safe guess that the biggest-selling, grocery-type canned foods were the most commonly fed brands. The other clue to brands is the use of the term “giblets” which is more common in the mass-market, less expensive foods; many of them are also fish-based. Many of these foods have white can liners, so those may be the higher risk ones. However, there are many different white liner compositions, so we can’t really say with any certainty that those are worst. Many white liners are probably fine.

      I do think that it’s easier to stay away from the highly implicated ingredients, “giblets” and fish. Fish is typically the most PBDE-contaminated ingredient in cat food.

      The size of the can may also be part of the link. Food in 3 oz. cans has a larger surface area in contact with the liner, so chemicals have more opportunity to leach into the food. It’s a peculiarity of the canning process that different sizes of the same brand and flavor of food may use a different liner for each size. If you decide to buy a bigger size, don’t leave it in the can; it’s best to store leftovers in a glass container in the refrigerator. Larger cans (13 oz) of Wellness and several other natural brands do not have pop-tops, so those may be the safest of all.

      It’s all very confusing, but the take-home message is this: stay away from the smallest cans, avoid fish and giblet flavors, and don’t shop for cat food in grocery and discount stores. The natural brands, due to their source and quality of ingredients, are far less likely to be a problem. Personally, I don’t hesitate to feed my four cats the natural brands from Only Natural Pet Store, including Wellness (a favorite at my house!). I also alternate canned food with homemade raw food.

      If you’d prefer to just stay away from canned foods, consider switching your cat to one of the excellent frozen raw diets such as Raw Advantage, Nature’s Variety, Bravo, or Stella and Chewy’s. Other alternatives include a homemade diet using meat with a complete supplement like Sojos, or a freeze-dried raw diet such as Only Natural, Nature’s Variety, Ziwi Peak, or Wysong Archetype. Remember that dry foods are not a good choice as the sole diet for cats due to their dehydrating effects. If you want to switch your cat to a different food, be aware that it takes time and patience; here are some tips on how to do it:

  2. Hello all,
    I too feed wellness canned and nutromax senior dry to both cats who are 18. Shadow has accelerated hyperthyroidism and am hoping he will live a few years more with tapazole and a cleaner diet.

    If I get another cat, I will likely go with raw and homemeade foods from the beginning.


  3. I have a hyperthyroid cat, and he is now doing quite well, found a natural remedy on a website in liquid form, five drops a day is working for him now, he was losing weight, hair and was way nervous. Now his hair is back and so is his weight. He is much calmer due to a calming collar found at petsmart. if anyone wants more info you can email me at
    his name is Smokie Jo Spunkmeister by the way and he is such a fun cat to live with

Leave a Reply