Hyperthyroidism is the most common hormonal abnormality in cats. Traditional treatments included radioactive iodine treatment to inactivate the tumor cells that cause excess secretion of thyroid hormone, or medication to suppress hormone secretion. Several years ago, it was found that an iodine deficient diet was just as effective as the traditional treatments for treating hyperthyroidism in cats.


The solution was revolutionary and substantially reduced the costs of treating this condition. Questions arose about this approach in multiple cat households, where it is impossible to successfully segregate food selections and where healthy cats would have access to the iodine restricted diets. Would healthy cats suffer if subjected to an iodine restricted diet? Recent research findings suggest that healthy cats are not affected by iodine deficient diets.


Hyperthyroidism and Iodine Deficient Diets for Cats


The thyroid hormone regulates body metabolism. Older cats with microscopic tumors of the thyroid gland secrete excess thyroid hormone, which increases metabolism. This excess secretion results in an increased appetite with weight loss. They often beg for more food and arouse owners late at night with howls of hunger. These cats also drink lots of water and have increased urination. The increased metabolic rate also causes an increased heart rate and an eventual heart murmur due to heart malfunction. The increased metabolic rate also affects kidney function and these cats are often in secondary kidney failure when the condition is diagnosed.


Thyroid hormone is absolutely dependent on iodine for proper function. Recent research found that depriving hyperthyroid cats adequate iodine in the diet decreased the thyroid hormone production. Like traditional treatments, this reduced the harmful effects of excessive thyroid hormone production. For the hypothyroid cat, this treatment approach was more affordable and as reliable for afflicted cat owners as the traditional treatment methods. But veterinary scientists were concerned about the effects of such diets on normal cats in multi-cat households. In these situations it is sometimes impossible to restrict access of normal cats to iodine deficient food.


New Research Findings on Iodine Restricted Diets for Cats*


At the recent Academy of Veterinary Internal Medicine Symposium I had an opportunity to meet with scientists who had developed the iodine deficient diet and their recent research into the effects of this diet on normal cats. Their findings were extremely encouraging.


Admittedly, their research population was limited, with 15 cats receiving a diet with adequate iodine and 15 receiving iodine amounts found in the hyperthyroid iodine deficient diet. But they did extend the research period to 18 months. This is far longer than most nutritional studies. Their findings concluded that no health problems were noted for healthy cats on an iodine restricted diet.    


The researchers admit that longer studies are necessary to conclusively prove that iodine deficient diets are safe for normal cats. However, this research suggests that owners of a hyperthyroid cat in a multi-cat household do not have to make Herculean efforts to ensure dietary segregation and can even feed the same food for all members of the household. Of course, caution should be taken for kittens exposed to iodine deficient diets. Their sensitivity could certainly result in problems and access to iodine deficient diets should be restricted until research in this group has been conducted.


Dr. Ken Tudor


*This study is not yet published.


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