We hear a lot about the need for iodine especially since billions of people around the world are suffering from this deficiency (World Health Organization estimates). Yet we also find articles about the risks of iodine and iodide ingestion published in many well recognized medical journals. This creates a great deal of confusion in the minds of physicians and the public.
No physician would ever deny the fact that we require iodine and iodide for our health. Yet from the literature iodine and iodide seem to be a double-edged sword with too little as well as too much being the cause of illness. How can we sort through this topic and find the truth?
Soy, Seaweed & Selenium
From The Medical Journal of Australia, 2010, we find several cases of reported thyroid dysfunction in adults associated with the ingestion of a brand of soymilk fortified with kombu (seaweed). This brand was found to contain high levels of iodine (and most likely iodide since kelp contains both).
Here we have their opening statement which just leads to the confusion. “Despite increasing awareness of iodine deficiency the potential for iodine toxicity, particularly from souces such as seaweed, is less well recognized.”
“In November 2008, a 36-year-old woman presented with a mildly elevated serum thyroid stimulating hormone (TSH) level. Her urinary iodine level was measured to exclude iodine deficiency; this level of iodine was markedly elevated at 4445 μg/L with a normal reference range less than 200 μg/L.”
You’ll notice here that this woman had her urinary iodine checked because they were looking for one cause of elevated TSH which is low iodine and low iodide. In this woman’s case the cause of her elevated TSH was from the iodine. I’ll explain this in just a moment.
“Three months later, a 38-year-old man presented with florid thyrotoxicosis (overactivity of thyroid gland). A scan result, in combination with his elevated urinary iodine level (1278 μg/L), indicated that iodine toxicity was the most likely cause of the thyrotoxicosis. He drank brands of soy milk other than Bonsoy, but also drank Bonsoy (includes seaweed) in takeaway coffee. After he ceased drinking all soy milk, his symptoms rapidly abated and his serum TSH level normalised 3 months later.” Was it the soy or was it the iodine, or both?
What most physicians don’t understand is that iodine and iodide increase the production of TSH. Why is this?
Both of these trace minerals are considered by the body to be precious, both elements having to do with survival and reproduction. (Note that the tissue which has the highest concentration of iodine, second only to the thyroid, is the ovary.) So when iodine and iodide are ingested the body has a way to store them. Various tissues including the thyroid, ovaries, breasts, salivary glands, prostate and others have small channels called sodium-iodide symports (NIS) which actively uptake iodide and some believe iodine (debatable).
When iodine and iodide enter the body these channels become activated. It wasn’t until just recently that we came to understand what actually stimulates the activity of these channels. It’s TSH. This hormone not only stimulates them but it also increases the number of them.
Therefore the ingestion of iodine and iodide stimulate TSH production. But elevated levels of TSH have other effects as well. TSH also stimulates thyroid cells to make thyroid hormones. But how?
TSH & Thyroid Hormone Production
Along the assembly line of thyroid hormone production we find the final product has atoms of iodine attached. But if we go back up that assembly line we find that one of the original steps is the formation of iodine from iodide. Thyroid cells do not absorb iodine. They absorb and trap iodide and use it when needed to make thyroid hormones. When a thyroid cell is stimulated to make its hormones this iodide is changed into iodine and the assembly line takes off. How does the thyroid cell change iodide into iodine?
Thyroid cells make hydrogen peroxide which oxidizes iodide to become iodine. And what stimulates thyroid cells to make hydrogen peroxide? Exactly, TSH.
Normally there is a kind of see-sawing between TSH and thyroid hormones. When thyroid hormones in the blood begin to decline, TSH production goes up. As TSH goes up then the thyroid’s production of its hormones increases. And as thyroid hormones enter the blood stream the production of TSH declines.
Yet if we continually ingest iodine and iodide TSH will remain elevated. This is what most physicians do not understand. This elevated TSH will continually stimulate thyroid cells to make more and more hydrogen peroxide which will eventually lead to thyroid cell irritation and inflammation (thyroiditis).
This is the danger or risk of taking too much iodine and iodide.
But this research is very narrow, looking at just one factor for thyroid dysfunction. This has its shortcomings. I would venture a guess that developing thyroid issues from ingesting kelp has a selenium deficiency. Selenium plays a very important role in thyroid hormone metabolism and in helping to reduce thyroid inflammation.
Genistein & Soy
It should also be noted that including soy in this journal study was another factor which wasn’t taken into consider.
Soy is known to produce estrogenic isoflavones with genistein being the primary one.
From the Journal of Neurological Sciences, 2009, “Genistein and diadzein from soy inhibit thyroperoxidase (a thyroid enzyme) that catalyzes (stimulates) iodination (the assembling of iodine to a protein to make the hormone) and thyroid hormone biosynthesis.”
This decrease in the synthesis of thyroid hormones due to soy would also lead to an increase in TSH (the see-saw).
I do not think that ingesting seaweed by itself would have created the severity of symptoms in the subjects of this study yet I am adamant about the use of selenium whenever using an iodine supplement.
Dr. Alexander Haskell, ND
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