“Doc, my cat eats constantly but still keeps losing weight!”

While there can be any number of causes for this, in a middle-aged or older cat an overactive thyroid is always one of the potential reasons atop our list.

Thyroid glands produce hormones that regulate metabolism. But when they are enlarged and producing too much thyroid hormone, they rapidly increase a cat’s metabolic rate. This causes, among other things, a dramatic increase in heart rate and blood pressure, and an increased demand for nutrients. These kitties literally cannot consume enough calories to meet their bodies’ increasing demands.

Untreated hyperthyroidism can cause heart failure or organ failure, but many cats just waste away. I have seen adult cats weighing less than 4 pounds, caused by uncontrolled hyperthyroidism. Many owners mistakenly believe that as long as their cat has a healthy appetite, it is OK, but this kind of weight loss can be fatal.

Hyperthyroidism can easily be diagnosed by your veterinarian through simple blood tests. With an exam and additional blood work, your vet can also tell what organs may be affected and what treatment option would be best for your cat. Today’s treatments can involve daily medication, surgery to remove the enlarged gland, or radioactive iodine treatment to destroy the abnormal thyroid tissue. Each treatment has its pros and cons – so only you and your vet can decide which option is best for your pet.

What causes hyperthyroidism?

Thirty years ago, hyperthyroidism was unknown in cats. Now it is their most commonly diagnosed hormone abnormality. Why? What has changed? These are questions that have plagued veterinarians for years. A new study from the Environmental Protection Agency may provide some insight.

The EPA analyzed normal and hyperthyroid cats. The hyperthyroid cats had blood levels of a chemical called PBDE (polybrominated diphenyl ethers) three times higher than normal cats – and 20 to 100 times higher than the average person. According to the EPA, PBDE is known to disrupt the endocrine system, which releases hormones.

Looking back, PBDE was first introduced in the 1970s, and the first feline hyperthyroidism cases started to appear roughly a decade later; it usually takes cats eight years or more to show signs of the disease.

PBDE is used in flame retardants found in fabric, furniture, carpet, mattresses, electronic equipment, TVs and cell phones.  According to Heather Stapleton, an environmental chemist from Duke University, PBDE leaks out of these products in the form of dust; it doesn’t break down very easily, and accumulates in the body’s tissue when ingested.

Cats may ingest higher levels of these compounds because they are lower to the ground, in constant contact with these chemicals – and, ironically, because of their impeccable grooming behavior. They ingest more household dust.

Higher levels of PBDE also have been found in canned cat food, specifically salmon, whitefish and chicken liver. This may be because PBDE dust leaks into the food chain, and larger fish such as salmon are higher on the food chain, therefore accumulating more PBDE.

A side note: EPA researchers, fearing cats may be “the canary in the coal mine,” have called for more study about PBDE and humans. PBDE has been found in human breast milk, and researchers are concerned about small children, who, like cats, are close to the ground and put everything in their mouths.

What can you do?  Watch for more studies about PBDE.  Limit the use of canned food with salmon, whitefish or chicken liver. Take your pets to your vet for their yearly exams – and remember, increased appetite and weight loss are never normal in any pet, of any age.