Iodine, raw feeding & feline hyperthyroidism
In the article about the supplements that I use in Néline and Praline’s diet, I mentioned that I add kelp as a source of iodine. In today’s article, I’m going to go into more detail about iodine, as it’s one of the essential nutrients for cats. ‘Essential’ means that cats cannot synthesize it by themselves and so it must be provided in their diet.
In this article, I will explain what iodine is, how much iodine your cat needs, in which foods you can find it, and more!
What is iodine?
Iodine is a mineral (an inorganic element) or, more precisely, a micromineral or trace element because it’s present in the body in very small amounts. While it’s present in small quantities, it doesn’t, of course, mean that iodine is useless. On the contrary, iodine participates in the synthesis by the thyroid gland of two hormones: thyroxine (T4) and triiodothyronine (T3). These hormones play a role in the regulation of the metabolism, in thermoregulation, in growth, in reproduction, in neuromuscular functioning, as well as in the integrity of the fur. [1][2][3]
An iodine deficiency can cause a rough coat, apathy, and goiter, which is an enlargement of the thyroid. In kittens, a deficiency in iodine can cause a failure to grow, skeletal deformities, skin lesions, and dysfunctions of the nervous system. Feline hyperthyroidism may be caused by an iodine deficiency.
It is important to note that an iodine excess can also cause a goiter, rough coat, as well as feline hyperthyroidism.
Feline hyperthyroidism is an important concern as it’s a relatively common disease in cats: around 10% of cats older than 10 years old are affected. It’s the most common endocrine disorder in cats. [5-11]
The symptoms of feline hyperthyroidism are increased hunger, excess drinking, increased urination, weight loss, hyperactivity, and an enlargement of the thyroid.
Since the late ’70s, the disease became more prevalent. Its causes are not well understood yet, but there are some theories on diets that are deficient or excessively rich in iodine, or on diets that have large variations in their iodine content. For all these reasons, I recommend being careful with the iodine content in the diet.
How much iodine does my cat need?
Now that we understand what iodine is, let’s look at how much our cats need. Here is where things start getting complicated. In fact, there are few studies on the feline iodine requirements and there is some debate on if the requirements defined by the NRC and the AAFCO are under- or over-estimations.
The latest study, published in 2009, determined the iodine requirement as 115μg per 1000kcal of diet. [4]
The current NRC recommendation for iodine, which was published in 2006 (before the 2009 study), is 350μg per 1000kcal.
The AAFCO, before the 2009 study, recommended 88μg and then adjusted the recommendation to 150μg to take into account the latest results (plus a safety margin).
A recent review recommended staying in the range of 125-500μg per 1000kcal. [7] I would be more conservative and I would recommend a range of 125-350μg. You will find a calculator at the end of the article if you want to determine how much daily iodine your cat requires.
The maximum iodine amount often recommended is 1000μg per 1000kcal, with some adverse effects that may start appearing at 2200μg per 1000kcal. [7]
The minimum seems to be 45μg per 1000kcal which has been fed to cats for up to 2 years without adverse effects. [4][12]
As we have seen before, both a deficiency or an excess in the iodine amount in a diet may cause thyroid issues in the long term, so it’s better to stay in the recommended range.
However, when analyzed, the range of iodine in industrial pet food varies dramatically, going from below the requirements to far above the safe upper limit. These variations could be one of the factors of the epidemic of feline hyperthyroidism, combined with other environmental factors. In one study, the range of iodine in industrial pet food varied from 50 to 38640μg per 1000kcal. [8]
Because a big variation in the iodine intake could be one of the causes of feline hyperthyroidism, I recommend feeding a regular quantity of iodine and avoiding feeding a big quantity once a week or even less often.
Where is iodine found?
Most of the iodine on earth is found in the seas: it is present in high quantities in fish, algae, mollusks, and seafood in general. It’s also present in eggs and milk. The amount of iodine in meat, vegetables, fruits, grains, and seeds is quite low, but there is some variation depending on the geographical area. If the soil is closer to the sea, the food will be richer in iodine when compared to the inland.
You can find iodine amounts in food in some nutritional databases such as the ones from France, Norway, Finland, Estonia.
I made some calculations of the amount of iodine in three different diets to give you an idea of how much iodine is present on average in a raw diet.
Example 1
I calculated the amount of iodine in the example of the NRC-balanced diet that I described in this blog article, minus the kelp as it is an iodine supplement as we will see later on.
The amount of iodine in the diet is 10μg, of which 8μg comes from the sprat and mussel. The daily requirement of iodine for my cat Praline (3.7kg) is 30μg. So, without the supplement and despite containing fish, only 33% of her requirements are covered by the diet. If it didn’t contain any fish or seafood, only 7% of the requirement would be covered.
Example 2
Let’s consider a PMR recipe with a daily ration of 120g, which is approximately 3% of Praline’s weight:
20g chicken necks, 20g beef hearts, 6g beef liver, 6g pork kidney, 12g mackerel, and 56g chicken breast.
This diet contains 14μg of iodine which is 46% of Praline’s requirement. Similarly, 10μg of the iodine in the diet comes from the fish. Without it, the diet would only cover 13% of her requirements.
Example 3
In this last example, let’s consider a PMR diet supplemented with iodine-rich food: oyster, mussel, fish, and egg.
27g chicken wings, 10g veal heart, 6g chicken liver, 6g lamb brain, 12g sardine, 5g mussel, 5g oysters, 10g quail egg, and 39g of pork.
The diet contains 20μg of iodine, which is 67% of Praline’s iodine requirement. Again, 17μg of iodine in the diet is coming from the seafood and quail egg. Without these, only 10% of her requirements would be covered.
To summarize, raw diets must be supplemented with iodine: as a rule of thumb, you can consider that the food will already cover 30% of the iodine requirement. The other 70% of the requirement will need to be covered with a supplement.
How to supplement the diet with iodine?
There are mainly 3 different options, often used in the raw feeding community: kelp, iodine drops, iodized salt.
While iodized salt isn't harmful, I do not recommend it as both sodium and chloride are already covered in a PMR raw diet.
Let’s talk about the two other options: kelp and iodine drops.
Kelp
Kelp designates a family of brown algae and not a specific species. As we have seen, algae are rich in iodine, and kelp in particular is extremely rich in it. Feeding dried powdered kelp (or in tablets) is an easy way to supplement iodine using whole food.
As we've seen in the previous paragraphs, it’s important not to supplement an excessive amount of iodine: as kelp is very concentrated, be careful with the amount you introduce in your cat's diet. Always choose a brand of kelp that indicates the amount of iodine and, if possible, that is standardized.
Finally, like most products of the sea, kelp can contain heavy metals, so try to select a brand that tests its products for heavy metals and, in particular, arsenic.
Iodine drops
A simple way to cover the iodine requirement is to just use an iodine supplement. The most common form of an iodine supplement is potassium iodide. It’s generally in a liquid form.
The advantage in comparison to the kelp is that it’s more standardized and there is no risk of the presence of heavy metals.
Thyroid gland and hyperthyroidism
You may have heard that raw diets cause hyperthyroidism. Or you may have heard about the recommendation of not giving too many chicken necks, as I wrote in my article about raw meaty bones.
Let’s take a closer look at these two claims.
Several reports were made, starting in 2012, of dogs eating a raw diet that caused hyperthyroidism. After a change of diet, the symptoms disappeared. However, similar subsequent cases were reported in dogs consuming canned food, as well as dogs consuming dry diets and treats. [15-20]
The common factor in all these cases is that the diet contained beef gullet. Some raw diets were made predominantly of minced beef gullet or neck and head parts. It was the same thing for the canned food. In several cases, the dogs were fed daily or regularly dried beef esophagus as treats.
In fact, all these parts are susceptible to contain thyroid tissue and, therefore, elevated levels of thyroid hormones T4 and T3, as well as iodine.
What we can learn from these cases is that raw feeding does not cause hyperthyroidism per se (as the same problems arose with canned food too), and that thyroid hormones are resistant to heat treatments. We should be careful about feeding tissue that contains thyroid, especially tissue from beef.
However, there was no report about cats: maybe because hyperthyroidism is so common in cats (contrary to dogs), so such incidents were not identified, or because cats are less likely to be fed a diet containing gullets.
Additionally, all the reports were about diets containing beef: this is probably due to beef being much bigger than chicken or pork and, therefore, containing more thyroid hormones. But there is no reason to believe that an excess of thyroid hormone from chicken neck wouldn’t be as harmful.
I didn’t find any information on the amount of hormones or iodine in chicken necks, and it’s difficult to evaluate what would be “too much”. I would highly suggest not giving chicken necks every day and not feeding beef meat from the neck, especially if the thyroid gland is not removed.
To conclude, iodine is almost always deficient in a raw diet, and a deficiency can have consequences on our cat's health. I recommend supplementing iodine using either kelp or an iodine supplement. However, the quantity needs to be relatively precise as an excess of iodine can be as detrimental as a deficiency. You can use the calculator below to determine how much you should add to the diet.
Finally, chicken necks are susceptible to contain a high amount of thyroid hormones and, for this reason, I would recommend not feeding them every day.
Supplement calculator
This calculator is made using the metabolic weight formula:
The inferior optimum is 12.5μg per kg/BW^0.67 equivalent to 125μg per 1000kcal
The superior optimum is 35μg per kg/BW^0.67 equivalent to 350μg per 1000kcal
Notes: 1μg = 1mcg = 0.001mg
1mg = 1000μg = 1000mcg
Other readings
Two articles from Linda Case on the issue with beef gullet : Got Gullet? and Give Up the Gullet
Can raw diets cause hyperthyroidism?
Sources
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