older-aged feline friends.
Hyperthyroidism, an overactive thyroid gland, has become some-thing of an epidemic in cats in recent years, and scientists from around the world have been trying to figure out why. Now, there's a convincing body of evidence suggesting that feline hyperthyroidism is an environ-mental disease caused by common chemicals lurking in household dust as well as in certain types of pet food.
The good news is that if it is chemicals in the home and food that are causing an overactive thyroid in your cats, then you may be able to protect your pets against this potentially deadly disease.
A burning problem
Vets first noticed a dramatic rise in feline hyperthyroidism in the 1980s, coinciding with the increased use of polybrominated diphenyl ethers (PBDEs) as flame retardants in consumer products. PBDEs are a group of chemicals routinely added to materials to reduce the chances of catching fire in a variety of products-from sofas, curtains and carpets to TVs, toasters and computers. So ubiquitous are these chemicals that they've been turning up in our house dust, food and even our bodies, as they are inadvertently eaten and inhaled (Environ Sci Technol, 2007; 41: 1584-9).
PBDEs are a particular problem for cats as they meticulously groom themselves, licking off dust that is likely to be contaminated with toxic PBDEs. The chemicals have also been found at high levels in cat food, particularly the canned fish-flavoured varieties.
The concern is that once PBDEs get into the body-be it animal or human-they can cause a host of toxic effects, including thyroid problems. In fact, PBDEs are known as 'endocrine disruptors'-chemicals that can interfere with the hormone system, and lead to adverse developmental, repro-ductive, neurological and immune effects.
Several studies have found a link between PBDEs and hyper-thyroidism in cats. In one study by Janice Dye and colleagues from the US Environmental Protection Agency (EPA), average PBDE levels were three times higher in older cats with overactive thyroids than in younger cats without the disorder. Overall, blood concentrations of PBDEs in cats were 20- to 100-fold greater than the PBDE levels usually found in people.
The researchers also analyzed the PBDE content of several cat-food brands, and found that canned fish and seafood flavours, such as salmon and whitefish, contained higher PBDE levels than dry or non-seafood canned items. They estimated that diets based on canned food could have PBDE levels 12 times as high as dry-food diets (Environ Sci Technol, 2007; 41: 6350-6).
Another study looked at PBDE levels in dust from the homes of hyperthyroid cats and those with normal thyroid function. PBDE concentrations were significantly higher in the dust from the homes of cats with thyroid problems. What's more, dust PBDE levels were related to the amounts of thyroid hormone thyroxine (also known as T4) circulating in the blood (J Toxicol Environ Health A, 2012; 75: 201-12).
More research is currently underway, but some scientists are already saying that chronic exposure to PBDEs may partly explain the epidemic of hyper-thyroid disease in older cats. As Janice Dye explains, PBDEs may be interacting with thyroid-binding proteins to displace thyroxine, and chronic exposure could lead to sustained increases in secretion of thyroid-stimulating hormone as well as thyroid gland enlargement. "When that happens," says Dye, "it's pedal to the metal, and the cat's thyroid makes too much thyroxine" (Environ Health Perspect, 2007; 115: A580).
Besides PBDEs, other chemicals commonly found in the home have also been implicated in feline hyperthyroidism. Bisphenol A (BPA), a plastics chemical known to leach from food-can linings into the foodstuffs contained in the can, is another common pollutant that cats may be exposed to and which could be playing havoc with their hormones. A Japanese study confirmed that the chemical is present in canned cat and dog food at detectable levels (Res Vet Sci, 2002; 73: 177-82).
Cats fed food from cans with easy-open lids are more likely to come into contact with BPA, it seems, as these cans have different interior coatings to make them more flexible. One study found that cats eating food from 'pop-top' cans were more likely to develop overactive thyroids compared with cats eating dry food (J Am Vet Med Assoc, 2004; 224: 879-86).
Other studies have also found a link between the consumption of canned cat food and a higher risk of feline hyperthyroidism (J Vet Intern Med, 1999; 13: 323-9).
Although no one appears to have investigated levels of BPA in cats yet or their relationship to hyperthyroidism, research in people shows that eating canned foods can cause urinary levels of BPA to soar. And BPA levels in urine have, in turn, been linked to changes in thyroid hormones (Environ Health Perspect, 2011; 119: 1396-402).
Other plastics chemicals, such as phthalates, are associated with similar effects.
Yet more chemicals that may have a part to play in feline hyper-thyroidism include pesticides and insecticides. A study in New Zea-land revealed that cats whose bedding was regularly treated with anti-flea products had a dramat-ically higher risk of hyper-thyroidism. This was also true of cats living in households where fly sprays were reported to be used often (N Z Vet J, 2005; 53: 53-8). Exposure to lawn herbicides, fertilizers and pesticides also appears to raise the risk of thyroid disorders in cats (Prev Vet Med, 1988; 6: 295-309). Again, these chemicals are known endocrine disruptors and so can have detrimental effects on health.
Protecting your pet
The good news is that it might be possible to prevent feline hyper-thyroidism, to some extent, by minimizing your cat's exposure to these toxic, hormone-disrupting chemicals. Here are some tips to help make your home healthier for your pet.
- Avoid feeding your cat canned food-particularly fish/seafood varieties.
- Choose a non-plastic material for your cat's water bowl.
- Vacuum regularly with a HEPA-filtered vacuum cleaner to limit your pet's exposure to toxic chemicals from house dust. Also, remove your shoes at the door, or use doormats, to avoid tracking pesticides and other contaminants indoors from outside.
- Replace older foam-based pet-bedding, and replace or reupholster any furniture with exposed or crumbling foam fillings, as flame retardants are likely to be found in them.
- Avoid flea collars and topical insecticides and, instead, vacuum often and bathe your pet regularly. Adding a few drops of tea tree oil to a herbal shampoo can help to repel fleas. For pets who don't like taking baths, mix a tea-spoon of tea tree oil in a cup of water and spray the mixture onto the animal's fur. Boosting your pet's immune system can also help to control fleas. Make sure your cat's diet contains adequate amounts of calcium, magnesium, potas-sium, phosphorus and zinc, as well as plenty of B vitamins, which are natural flea and tick repellents. Brewer's yeast and rice bran contain high levels of all the B vitamins. Adding garlic to your pet's diet may also help.
- Care for your garden without herbicides or insecticides. And avoid using pesticides inside the home, too. For non-toxic alternatives, see WDDTY vol 19 no 2.
Factfile: Watch out for these symptoms
- Weight loss
- Increased appetite
- Hair loss
- Increased water-drinking
- Rapid heart rate
- Poor-quality hair coat
Factfile: Homeopathy for hyperthyroidism
If your cat's been diagnosed with hyperthyroidism, your vet may suggest life-long antithyroid drugs or surgery to remove the affected thyroid tissue, both of which come with serious risks. Another option is radioactive iodine treatment, but this can be very costly.
An alternative worth considering is homeopathy. The Animal Medical Center of Watkins Park in Cheltenham, MD, in the USA, recently used individualized homeopathic treatment in four cats with overactive thyroids. All four cats became symptom-free and three saw their thyroid hormone levels return to normal (Homeopathy, 2011; 100: 270-4).
For advice on treating your pet with homeopathy, contact Ainsworths homeopathic pharmacy (tel: 01883 340 332; website: www.ainsworths.com).
WDDTY VOL. 23 NO. 1, APRIL 2012