Is There a Link Between Fish Oil and Hyperthyroidism in Cats?

A rumor about a possible link between iodine toxicity, fish oils, and and feline hyperthyroidism is flying around on the Internet. So what's the real deal? The short answer is--excellent quality, purified fish oils are not a problem--but many commercial products could be implicated. Read on for more in

Iodine, a basic chemical element and a necessary nutrient, is stored in animals' bodies in the thyroid gland. Pet foods or products that use fish, fish meal, or fish oils that are derived from processing or pressing the whole fish (including the thyroid) will contain that iodine. Cod liver oil is pressed from fish livers after they are removed from the fish, and is not a significant source of iodine. The best fish and cod liver oils are also molecularly distilled, which further removes virtually all solids and other impurities. The purest Omega-3 fish oils contain, at most, a tiny trace of iodine. Good quality, fresh Omega-3 fish and cod liver oils are not the problem when it comes to iodine.

Most of the iodine consumed by our pet cats comes from commercial cat foods, primarily from the mineral pre-mixes used in these foods. Minerals, including iodine, are often included in great excess. Iodine is difficult and expensive to test for, so it's cheaper and easier for pet food makers and suppliers to add way more than necessary to make sure the food is not deficient. They don't care if too much gets into cat food. One study of adult and growth dog and cat foods found 10-100 times the recommended amount for many minerals. There are few maximum limits set (12 for dog food, 4 for cat food). Iodine has a maximum limit for dog food, but no similar maximum in cat food. This approach makes the food cheap, but it can cause a host of physical problems for our cats.

In addition, you may recall that a study out of Purdue University found an association between certain flavors and types of cat food and hyperthyroidism pointed out that pop-top cans (most of which contain BPA in their linings), giblets (by-products), and fish had the highest associations. Again, the fish going into these products are whole feeder fish, damaged or spoiled fish, or fish parts (heads, tails, internal organs) not wanted for human consumption. Iodine levels in fish meal made from these products is likely to be quite high. Fish meal is a common ingredient in cat food and on many labels is credited as the source of Omega-3 fatty acids. In reality, it is a very minor source of Omega 3's and is used in cat food mainly for flavoring. Fish oil derived from similar sources could be similarly contaminated, which is why we stress choosing a distilled, pharmaceutical grade fish oil for your cat (I personally use and recommend Nordic Naturals).

Further studies have also suggested a link between fire-retardant chemicals and feline hyperthyroidism. It turns out that cheap pet food ingredients--particularly fish and by-products--are the most likely to be contaminated with these chemicals. This could not only account for the Purdue findings, but it could also be creating a "double-whammy" for our cats in terms of exposure to these toxins.

Pure, properly processed fish and cod liver oils contain (at most) trace levels or zero iodine, and certainly are not implicated in any situation of iodine overdose. The fact remains that Omega-3's are seriously deficient in virtually every pet food, raw food, and even homemade food for pets, because livestock and poultry raised in North America are fed on grains, which shifts the natural fatty acids to mostly Omega-6s. Omega-3 fatty acids are an essential component of your cat's diet, and must be supplemented for optimal levels to be reached.

Dr. Jean Hofve is a retired holistic veterinarian with a special interest in nutrition and behavior. Her informational website, http://www.littlebigcat.com, features an extensive free article library on feline health and pet nutrition (including articles on Omega-3 fatty acids, cat foods, and feline hyperthyroidism), as well as a free e-newsletter. She is a certified Medicine Woman within the Nemenhah Native American Traditional Organization who uses holistic remedies as a part of body-mind-spiritual healing.

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