Hyperthyroidism in Cats

By Dr. Karen Becker

Recent research has revealed that yet another chemical substance found in households may be contributing to feline hyperthyroidism, a disease that affects a significant percentage of cats over the age of 10. The chemicals are called per- and polyfluoroalkyl substances (PFAS), and they are widely used as water and oil repellents. According to ScienceDaily:

“PFAS are a family of more than 3,000 structures of highly fluorinated chemicals used in industrial processes and consumer products, such as protective coatings for carpets, furniture and apparel, paper coatings, insecticide formulations, and other items.”¹

PFAS are used in many industrial applications calling for nonstick or slick surfaces, such as food packaging, stain- and water-resistant fabrics, nonstick cookware and firefighting foam. These chemicals are now ubiquitous in our environment, having migrated into the air, household dust, food, soil, and ground, surface and drinking water.

Study Links PFAS Chemicals to Hyperthyroidism in Cats

For the study, a team of researchers at the California Environmental Protection Agency looked at blood levels of PFAS in two separate groups of Northern California kitties, most of which were at least 10 years old. The first group of 21 was evaluated between 2008 and 2010; the second group of 22 was sampled between 2012 and 2013.²

The researchers observed that the higher the blood levels of PFAS, the more likely the cat was to be hyperthyroid. One type of PFAS in particular, perfluorooctanoic acid (PFOA) was significantly higher in hyperthyroid kitties. These findings “… may indicate a possible link between PFAS levels and cat hyperthyroid, warranting a larger study for further investigation,” according to the research team.

In a bit of good news, the scientists noted a slight decline in PFAS blood levels between the first group of cats tested eight to 10 years ago, and the second group tested more recently. This mirrors recent results in humans as more companies phase out use of these chemicals, and presumably, as people gradually replace PFAS-treated household items.

Reducing Your Family’s and Pet’s Exposure to PFAS

Your best bet is to avoid all products that contain or were manufactured using PFAS, which will typically include products that are stain-resistant, waterproof or nonstick. From the Environmental Working Group:³

Find products that haven’t been pre-treated and skip optional stain-repellent treatment on new carpets and furniture

Cut back on fast food and greasy carryout food, since these foods often come in PFC-treated wrappers

Especially when buying outdoor gear, choose clothing that doesn’t carry Gore-Tex or Teflon tags, and be wary of all fabrics labeled stain- or water-repellent

Avoid nonstick pans and kitchen utensils — opt for stainless steel or cast iron instead

Pop popcorn the old-fashioned way, on the stovetop, since microwaveable popcorn bags are often coated with PFCs on the inside.

Choose personal care products without “PTFE” or “fluoro” ingredients; also avoid Oral-B Glide floss, which is made by Gore-Tex

It’s also important to filter your pet’s drinking water, and yours, to remove contaminants such as fluoride, chlorine, heavy metals and others. Household tap water typically contains enough toxic minerals, metals, chemicals and other unhealthy substances to damage your pet’s health long term.

Flame Retardants: Another Enemy of Indoor Kitties

Polybrominated diphenyl ethers (PBDEs), or flame retardants, are another type of household chemical that has been linked to overactive thyroid in cats, and a 2017 study confirmed the results of earlier studies that prove the high levels of PBDEs measured in indoor kitties are from house dust.⁴

PBDEs have been used since the 1970s in textiles, electronics and furniture to prevent them from burning, but like PFAS, they aren’t chemically bound to the product material, so they drift into the environment and cling to particles in the air such as house dust.

A number of these chemicals have been banned for use in household products, but they are extremely persistent and can leach into the environment for many years. Contaminated household dust can be inhaled as well as ingested, and can have an adverse effect on the health of kitties.

Brominated Flame Retardants Are Known Endocrine Disruptors

Prior studies of PBDE blood levels in cats have focused primarily on potential causes of feline hyperthyroidism, however, the intent of this study was to measure levels in healthy cats to establish their dust exposure.

The researchers took “paired samples” from the homes of each of the cats, meaning they took both dust samples and blood samples at the same time. They found evidence not only of brominated and chlorinated contaminants currently in use, but also chemicals that have been banned for decades. According to study co-author Jana Weiss, Ph.D.:

“By taking paired samples, we have greater insight into the environment that the cats live in. Moreover the cats in the study spent the majority of their time indoors and therefore air and dust in the home is expected to contribute more than the outdoor environment.”⁵

The study results are a heads up not only for cat guardians, but also anyone with small children, because both kitties and kiddos engage in a lot of “hand-to-mouth activities.”

“The brominated flame retardants that have been measured in cats are known endocrine disruptors. It’s particularly serious when small children ingest these substances because exposure during development can have consequences later in life, such as thyroid disease,” said Weiss.

Minimizing PDBE Exposure at Home

Most new foam products are not likely to have PBDEs added. If you have foam items in your home, office or vehicle that were purchased before 2005, however, they probably contain PBDEs. The Environmental Working Group offers the following tips to help limit your family’s and pet’s exposure to PBDE-containing products:⁶

Whenever possible choose PBDE-free electronics and furniture; PBDEs shouldn’t be in mattresses, couches and other foam products sold in 2005 or later, however they’re still put in some new televisions and computer monitors

Avoid contact with decaying or crumbling foam that might contain fire retardants, including older vehicle seats, upholstered furniture, foam mattress pads, carpet padding and kid’s products made of foam

Use a high-efficiency particulate air (HEPA) filter vacuum cleaner, since these vacuums capture the widest range of particles and are also good for reducing lead or allergens in house dust

Replace couches, stuffed chairs, automobile seats and the like that have exposed foam (if you can’t afford to replace them, cover them with sturdy cloth and vacuum around them frequently)

Don’t reupholster your older foam furniture, especially in homes where children or pregnant women live

Be careful when removing or replacing old carpet, since PBDEs are found in the foam padding beneath carpets; isolate the work area with plastics, and avoid tracking construction dust into the rest of your house

The replacement chemicals for PBDEs in foam are not fully tested for their health effects, so buy products made with natural fibers (like cotton and wool) that are naturally fire-resistant and may contain fewer chemicals

Did You Know PBDEs Are Also in Commercial Cat Food?

The same researchers who published the 2017 study I mentioned earlier also measured PBDE levels in cat food (both canned and kibble) matching the diets of the kitties in the study. They found that blood levels of PBDEs in the cats also significantly correlated with concentrations of those chemicals in the cat food.

In addition, another recent study concluded that fish-flavored cat food is a problem.⁷ A team of Japanese scientists evaluated cat food and feline blood samples and discovered that the type of polychlorinated biphenyl (PCB) and PBDE byproducts found in both the food and blood samples are derived from marine organisms.

The researchers were also able to simulate the way in which the bodies of cats convert the type of chemical present in the food into the type of chemical seen in the cats’ blood samples.

Based on their results, the team concluded the byproducts detected at high levels in cats’ blood samples likely came from fish-flavored food and not exposure to PCBs or PBDEs. However, further work is needed to determine the link between the metabolites (byproducts) and hyperthyroidism. If you’re wondering how these chemicals wind up in fish-flavored cat food, Dr. Jean Hofve of Little Big Cat explains it very well:

“There is a link between the feeding of fish-based cat foods and the development of hyperthyroidism, which is now at epidemic levels. New research suggests that cats are especially sensitive to PBDEs … [which are] found at higher levels in both canned and dry cat foods than dog foods; and more in dry than canned cat foods.

Fish-based foods are even worse, because marine organisms produce PDBEs naturally and can bioaccumulate up the food chain to high levels in fish; this compounds the exposure cats get from fabrics and dust.”⁸

5 Tips to Help Prevent Hyperthyroidism in Your Cat

1. Rid your environment of flame-retardant chemicals
2. Provide an organic pet bed
3. Feed a nutritionally balanced, fresh, species-appropriate diet to control iodine levels in your cat’s food, since iodine has also been linked to hyperthyroidism
4. Avoid feeding your cat a fish-based diet, since seafood is a very rich source of iodine, and cats aren’t designed to process a lot of iodine
5. Avoid feeding soy products to your kitty, as they have also been linked to thyroid damage

I also recommend checking your cat’s thyroid levels annually after the age of 7.