Hyperthyroidism in Cats and Flame Retardants
The relationship between hyperthyroidism in cats and flame retardants may seem a bit unusual. According to the authors of a new study in Environmental Science & Technology, however, there appears to be a link, while another study had different findings.
Hyperthyroidism is characterized by the overproduction of the thyroid hormones, triiodothyronine (T3) and thyroxine (T4), but mostly the latter. Elevated thyroid hormones raise the metabolism rate, which places a great deal of stress on the organs. Cats who are not treated can die from the disease.
The National Resources Defense Council explains that exposure to toxic flame retardants, which are found in items such as furniture, curtains, carpet, electronics, baby items, and appliances, has been linked to a variety of health problems in people. Some of them include risk of cancer, male infertility, early puberty in females, lower IQs and attention problems, and low birth weight babies.
Cats can be exposed to flame retardants from these and other items in the home. The toxins can accumulate in dust, which in turn can settle on a cat’s fur and be consumed when cats groom themselves.
Several flame retardants are on the market, and one type (polybrominated diphenyl ethers, PBDEs) was removed from the US market in 2005. However, items made before that time may be hazardous. In addition, different countries have different rules about the use of these toxins, and other flame retardants used as alternatives for PBDE could be harmful as well.
Hyperthyroidism in cats studies
In a new study conducted in Sweden, the researchers analyzed blood samples from 37 cats with hyperthyroidism and 23 cats who had normal thyroid function. The cats with hyperthyroidism had elevated levels of polybrominated diphenyl ethers (PBDEs). They also found another flame retardant called BB-209 (discontinued in 2000) in all of the cat blood samples.
The authors noted that while the presence of the flame retardants in the cats’ blood does not prove the chemicals caused the thyroid disease, it does suggest a link.
In an Australian study, the authors came to a different conclusion. Their investigation, which included cats with and without hyperthyroidism, evaluated the cats’ serum and house dust samples for PBDE levels. The results did not support a role for the flame retardant in the development of feline hyperthyroidism.
More about hyperthyroidism in cats
Hyperthyroidism affects more than 10 percent of older cats. The most common symptoms are weight loss and excessive appetite, as well as aggression, hyperactivity, vomiting, rapid heart rate, restlessness at night, increased drinking and urination, nervousness, and poor hair coat.
The vast majority (about 98%) of feline hyperthyroidism is associated with a benign enlargement of the thyroid. Thyroid cancer is the cause in only about 2 percent of cases.
The possibility that flame retardants could be a cause of hyperthyroidism in cats has been raised in the past. According to Lisa Pierson, DVM, development of this thyroid disease in cats may be associated with the following:
- Iodine levels in cat food that are either too high or too low
- Bisphenol A (BPA), which is an endocrine disruptor. BPA can be found in the coating of some pet food cans.
- PBDEs, which can be found in high concentrations in house dust and some fish. Therefore, cat foods high in fish may contribute to this disease as well.
- Soy in cat food, since this food product is known to disrupt the function of the thyroid gland. Many cat foods on the market contain soy and soy products
The exact causes of hyperthyroidism in cats is still not known. If your cat displays the signs and symptoms of this thyroid disease, you should see a veterinarian as soon as possible.
Chow K et al. Evaluation of polybrominated diphenyl ethers (PBDEs) in matched cat sera and house dust samples: investigation of a potential link between PBDEs and spontaneous feline hyperthyroidism. Environmental Research 2015 Jan; 136:173-79
Environmental Working Group
National Resources Defense Council
Norrgran J et al. Higher PBDE serum concentrations may be associated with feline hyperthyroidism in Swedish cats. Environmental Science & Technology 2015 Apr 21; 49(8): 5107-14
Lisa Pierson, DVM