Excess Iodine implicated in Thyroid disease: RDA's for Iodine in Dogs ...are they too high?

[Iceburg]

I raise this important topic for 4 reasons:

1) I recently proved that one of my dogs had suffered needlessly for more than 2 years due to a diet induced case of hypothyroidism(documented here at OurDogsOnline.com). This was the second dog (different breeds) of mine in the last 5 years that had been diagnosed with autoimmune thyroid disease.

2) I have noticed that thyroid disease (and associated symptomatic conditions) is one of the most common ailments reported on-line.

3) The National Research Council's RDA with respect to iodine (approx 300 mcg for a 50 lb adult dog) is more than triple the human RDA (approx 100 mcg) for an adult human weighing 3 times as much ... so potentially 9 times greater on the basis of weight alone.

4) Lastly, I have noticed that many commercial dog foods include kelp or seaweed as a key ingredient, often in unspecified quantities. One gram of kelp of the species Laminaria digitata contains approximately 5mg of iodine. The iodine content in 17 different kelp supplements studied by one group of researchers varied from 45 to 57,000 mcg per tablet or capsule!(1) Further many home-made dog food recipes seem to include kelp as a necessary dietary component of well-being ...why else would they call it "healthy powder"?

With the increasing number of both dogs being diagnosed with hypothyroidism, and the hype around the benefits of kelp, I feel it necessary to ask the question -- are we putting too much iodine in their diet?

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Some facts and scientfic studies that suggest yes -- we may be ingesting too much iodine in both our own and in our pets' diet...

In humans, the RDA for iodine is approx 40 to 200 mcg per day . Most nutrtional experts use 100 mcg of iodine per day as a target RDA.

One gram of kelp of the species Laminaria digitata contains approximately 5mg (5000 mcg) of iodine -- ie. 50x the upper limit RDA.

In Canada and the US table salt is iodized at a rate of 100 ppm. So 1 gram of salt contains 100 mcg of iodine (approx. the RDA for most adults). One teaspoon of iodized salt contains 400 mcg of iodine.

Iodine is considered to be an important environmental agent known to increase the risk of thyroid autoimmunity. Too much iodine or too little iodine can have very consequential effects on thyroid function. Several studies support a role for iodine in the initiation and promotion of auto-immune thyroid disease.The well known side effects of iodine include iodine induced hyperthyroidism and hypothyroidism. It has been shown that the introduction of iodine in a previously iodine deficient population may precipitate the emergence of thyroid autoimmunity. Thus, epidemiological studies have shown that appearance of thyroid autoantibodies has been associated with salt iodination in iodine-deficient regions. In addition, animal studies have confirmed that high iodine intake accelerates autoimmune thyroiditis in autoimmune-prone animal models. See Medical Journal Ref's (2), (3), (4).

The American Thyroid Association recommends that the low-iodine diet (used in the treatment of thyroid cancer patients) include less than 50 mcg of iodine per day. (Source 2) Besides iodized salt, the following food items contain copious amounts of iodine: seafood products, dairy products, egg yolks, baked products, red dye#3, molasses, soy products, some beans (red kidney beans, lima beans, navy beans, pinto beans, and cowpeas), fresh meat, and some rices.

I'm very interested to hear your thoughts, opinions and experiences with iodine, and of course your experiences with any thyroid problems in your pets.

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Medical Journal References (MJR's)

(1)Human intake of arsenic and iodine from seaweed-based food supplements and health foods available in the UK. Norman JA, Pickford CJ, Sanders TW, et al. , Food Addit Contam . 1988;5:103–109.

(2)Effect of Iodine Restriction on Thyroid Function in Patients With Primary Hypothyroidism.
Kanji Kasagi, Masahiro Iwata, Takashi Misaki, Junji Konishi
Thyroid 13(6):561-567, 2003. © 2003 Mary Ann Liebert, Inc.
Posted 09/04/2003
http://www.medscape.com/viewarticle/459924_print

(3) Control of efficiency and results, and adverse effects of excess iodine administration on thyroid function. Koutras A. , Ann Endocrinol (Paris) 57: 463-469, 1996.

(4)Chronic autoimmune thyroiditis. Dayan CM, Daniels GH., N Engl J Med 335: 99-107, 1996.

Other Reading
Kelp is a good source of bioavailable iodine. One gram of kelp of the species Laminaria digitata contains approximately 5mg of iodine.

Health Canada advises against use of SEAVITE products containing iodine
Health Canada is advising consumers not to use SEAVITE Premium Atlantic Kelp Blend and SEAVITE Premium Atlantic Kelp Tablets. These products, when consumed according to the instructions on the label can provide 25 times the recommended daily allowance (RDA) per day of iodine for adults; and could lead to serious adverse health consequences.
http://www.hc-sc.gc.ca/ahc-asc/media/advisories-avis/2003/2003_27_e.html

5000 mcg of Iodine in Maine Coast Sea Vegetables
Maine Coast Sea Vegetables offers two types of Kelp. Whole leaf kelp (Laminaria longicruris) has approximately 450 mcg. (micrograms or parts per million) iodine per gram. Our milled kelp (Laminaria digitata), sold in bulk and in our Sea Seasonings, has even higher amounts, about 5000 mcg. In comparison, Dulse contains 50 mcg per gram. These amounts are approximations as there is variation depending on season of harvest and the age of plant.
http://www.seaveg.com/faq3.php

[BrklynLiberal]

1. Thanks for this inof. I am looking into the iodine content of my dog's food.

I wonder if this is true of cats as well They seem to suffer from a lot of thyroid problems also.

[Iceburg]

3. Possibly...You might also look at the soy content in the chow

I am currently reviewing a signficant body of literature on the dark side to soybean of which many byproducts are used in pet foods. Soy has been purported to have a role in thyroid-related problems.

This past week a poster (who suffers from hypothyroidism) alerted me to its potential cause/effect relationship. So I did a bit of poking around in the medical journals and sure enough there was some compelling evidence that soy may be implicated in thyroid disfunction and immune disorders.

This general/layperson's article in Mother Jones (2004) encapsulates many of the more recent findings. It is also accompanied by a full set of references.

Wrt to iodine,(and other additives) the biggest problem is that the pet food companies do not disclose how much is alleged to be in the formulas, and even if they did they have an astoundingly bad track record for getting the quantities of food items wrong. Kelp, a huge source of iodine with great variabilty in iodine content, is routinely added to most dog foods now on top of calcium iodate. Check out these dog food comparisons. Most contain both kelp & calcium iodate!

What the hell is going on?? Who's designing this chow?? How many sources of iodine do we need? And who's measuring it?

[Iceburg]

5. Some additional links on iodine, hypothyroidism & testing

Canine Hypothyroidism, An Overview
http://www.vet.uga.edu/vpp/clerk/bell/index.php

Canine Autoimmune Thyroid Disease And Symptoms
http://siriusdog.com/articles/canine-autoimmune-thyroid.htm

Thyroid Testing In Dogs
http://siriusdog.com/articles/thyroid-test-dogs-t3-t4.htm

Total Thyroxine (TT4) and Total Triiodothyronine (TT3) Methods
http://www.medscape.com/viewarticle/452666

Thyrotropin/Thyroid Stimulating Hormone (TSH) Measurement
http://www.medscape.com/viewarticle/452667

Effect of Iodine Restriction on Thyroid Function in Patients With Primary Hypothyroidism
http://www.medscape.com/viewarticle/459924_print

Iodine Induced Hypothyroidism
http://endo.endojournals.org/cgi/rapidpdf/en.2007-0082v1.pdf

Review of iodine
http://www.food.gov.uk/multimedia/pdfs/evm0006p.pdf

Thyrotoxic periodic paralysis
http://www.nlm.nih.gov/medlineplus/ency/article/000319.htm

Miscellaneous
http://www.merckserono.net/servlet/PB/menu/1271740/index.html

[BrklynLiberal]

6. Thank you so much for all the info!

[Holly_Hobby]

2. Yes.

I agree that Kelp is one cause.

I have one dog with hypothyroidism, and buried another with hypothyroidism. They were both fed kibble containing kelp. The dog that is still living was put on a raw diet. Within several months, he had an intolerance to warmth and was panting. A blood draw indicated a lower dose of Soloxine thyroid hormone. He was put on once/day dosing instead of twice/day. The warmth intolerance stopped, as well as the panting.

Can I explain how a thyroid can start working somewhat properly again after changing the diet? No. But it happened. That's all the proof I needed to know that kelp should not be fed. Unfortunately, he was fed that kibble for 6 years, so some of the damage to the thyroid is permanent.

I think once humans intervene in what Nature provides for us and our animals, we're asking for trouble.

[Iceburg]

4. Wow ...thanks for sharing that story

That is more or less the I have had with my little aussie. Sadly, I also had a previous dog (a springer spaniel) that suffered thru years of hypothroidism (I just didn't know enogh at the time) and finally died suddenly of Immune Mediated Hemolytic Anemia -- all brought on by the shit in the commercial feed.

[Holly_Hobby]

7. So sorry to hear about your dogs

I lose lots of sleep due to the guilt of blindly following my vet's advice about what to feed my dogs. Never again!

:hug: