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