Effects of Increased Iodine Intake on Thyroid Disorders

Effects of Increased Iodine Intake on Thyroid Disorders

Many of the most persistent questions here, and in many other places that thyroid is discussed, concern iodine. Should I take an iodine supplement? Is it OK to take Lugol's solution? Someone said avoid all iodine, is that right? Is amiodarone the cause of my thyroid problem? Are only Hashimoto's sufferers supposed to avoid iodine? And many, many more.

Not for one minute do I blame the people asking the questions. If you don't know, ask! But when it comes to iodine it isn't just the new patients who don't know, it seems to be almost everyone! (I definitely include myself here.) So when a paper comes out expressly looking at the what happens when iodine intake increases, as happens with any form of supplementation, it seems worth a look.

As always, you can make your own judgements, and then post your opinions and comments.

Endocrinol Metab. 2014 Sep;29(3):240-247. English.

Published online Sep 25, 2014. dx.doi.org/10.3803/EnM.2014...

Copyright © 2014 Korean Endocrine Society

Effects of Increased Iodine Intake on Thyroid Disorders

Xin Sun, Zhongyan Shan and Weiping Teng

Department of Endocrinology and Metabolism, Institute of Endocrinology, Liaoning Provincial Key Laboratory of Endocrine Diseases, The First Affiliated Hospital of China Medical University, Shenyang, China.

Corresponding author: Weiping Teng. Department of Endocrinology and Metabolism, Institute of Endocrinology, Liaoning Provincial Key Laboratory of Endocrine Diseases, The First Affiliated Hospital of China Medical University, No.155 Nanjing North St, Shenyang 110001, China. Tel: +86-24-8328-3294, Fax: +86-24-8328-3294, Email: twp@vip.163.com

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.


Iodine is a micronutrient essential for the production of thyroid hormones. Iodine deficiency is the most common cause of preventable mental impairment worldwide. Universal salt iodization (USI) has been introduced in many countries as a cost-effective and sustainable way to eliminate iodine deficiency disorders for more than 25 years. Currently, the relationship between USI and iodine excess has attracted more attention. Iodine excess can lead to hypothyroidism and autoimmune thyroiditis, especially for susceptible populations with recurring thyroid disease, the elderly, fetuses, and neonates. Nationwide USI was introduced in China in 1996. This review focused on the effects of iodine excess worldwide and particularly in China.

Keywords: Iodine excess, Universal salt iodization, Thyroid diseases.


The full paper is available on-line, including tables. Please go off and read it.


17 Replies

  • Looks like a very big no no to iodine supplementation, Rod. Not good for a disordered thyroid and it may disorder an otherwise healthy thyroid.

  • Certainly does, but there are plenty who disagree and take phenomenal amounts of iodine!

    Like everything else, the truth is probably much more complicated.

  • There is evidence from other studies that increasing iodine in a selenium poor situation will create problems. Selenium was not mentioned in this study.

  • And a very recent one which mentions cobalt in a similar vein.

  • Rod, interesting that TSH levels are increasing in the Chinese people. The Western style diet has also increased in China. As gabkad said I wish they would have looked at selenium levels also. The U shaped curve seems to be the prevalent model. PR

  • I have been doing alot of reading on this lately and I think I am slowly getting to grips with it in the hope of being able to offer advice on iodine supplementation in pregnancy.

    Ok so what I have found so far leads me to the conclusion similar to the evidence such as the study above. The situation in China was that it was classed as severely iodine deficient which in itself causes thyroid problems such as hypo and hyper. To then introduce high concentrations of iodine through iodised salt is obviously going to cause an already damaged thyroid population  problems ( I'm thinking similarly to severely hyper/hypothyroid person then taking a high dose of levo/NDT)

    There appears to be a thin line between deficiency and excess (a bit like balancing TSH etc) and therefore we can't advise for or against....or can we?

    Looking at it logically the U.K. is classed as mildly iodine deficient (Bath et al, 2013) with a study of U.K. schoolgirls in Surrey showing over 50% deficient (Vanderpump, 2011) even a mild deficiency can alter the function of the thyroid (Zimmerman, 2009)

    The main source of iodine in the U.K. is milk/yoghurt via fortified cattle feed (increased iodine secretion  during lactation in all mammals) although not so much in organic milk! The other main source is fish if someone does not consume sufficient of either of these then they may need supplementation.

    Contra-indications are obviously auto-immune thyroid disorders and thyroid cancer where the balance is far more volatile. However iodine is still required for T4-T3 conversion if my understanding is correct? Although still trying to get my head around the chemistry of it.

    I know levels of iodine can interfere with thyroid function therefore in my opinion should be treated with the same caution as thyroid replacement medication?

    The W.H.O. recommends intake 150mcg/day rising to 250mcg/day for pregnant women. The best sources being dietary. If sufficient milk, yoghurt and fish (jaffa cakes are rich in iodine too) consumption, supplementation should not be needed. If it is not then supplementation may be needed to support thyroid function.

    There are many more factors that I'm still delving into.

  • Iodine and selenium can both be very patchy across China. A British Geological Survey study into both factors a number of years ago produced a complicated and somewhat non-obvious picture.

    Is that all makes of Jaffa cake? :-)

    Not sure about the iodine needed for conversion - the process of conversion releases iodine.


  • What about chocolate generally? I'd love to have a good reason to eat chocolate! :-)

  • I believe there were similar results in other countries deemed as severely iodine deficient in fact I believe one of the south Americas had a more severe curve because they had huge doses added to the salt and use quite alot in their cooking, but I need to go back to that research when I find it.....that was a great brain fog day!

    Possibly depends on the jaffa cake orangey bit (I believe its in the colourant they use......not the chocolate sorry

  • Still looking at the selenium vs iodine and interaction within the cells it's all very complicated and molecular.....not my best area

  • Have a look at this paper:



  • Perfect thank you!

    I think Brazil was the location of the study I was talking about yesterday where they put too much iodine in the salt and it was left unmonitored with an increase in auto-immune thyroid disorders!

    2003 sounds about the right time....I really need to find it!!

    I'm trying of collate all evidence found so if you come across anymore please link me in!!

  • I have been reading David Brownstein, Iodine -why your body needs it. I agree one should be cautious with supplementing Iodine. What I have read is that Selenium levels are very important. The western diet is generally low in selenium. The book also gives plenty of research references about why the modern diet is low in Iodine. I am hypothyroid on levo 100mcg and had high TPO antibodies diagnosed. I have got rid of the antibodies by eating a gluten and lactofree diet. A recent urine test showed that my Iodine levels are at 20 compared to a normal level of 150-199! At the moment I am using sea salt and B vits to help rid my body of halides/heavy metals which I know are a problem for me. In a couple of weeks I will try using Lugol's Iodine to increase my Iodine levels. I will continue to have private tests to check Iodine levels in urine.

    There is no help from NHS for those of us that have Hashi's and as for checking patient's Iodine levels, I think most NHS docs would think you were mad if you requested it. Iodine is the most important element for the thyroid to function properly. I have learned a lot from this site including ensuring that vitamin and mineral levels are important and should be supplemented if necessary. As far as I am concerned, the Iodine is the missing factor in my health and I shall be giving it a cautious trial.

  • My experience with iodine was similar to this. I've been wary of iodine ever since.

    Very interesting article, Rod. Thank you for posting.

  • Interesting article - thanks for posting. Personally I have never supplemented iodine and do not consume a lot of dairy or fish. My autoimmune thyroiditis is more likely to have been caused by other factors including soya consumption if reports that this is murder for the thyroid can be substantiated.

  • From what I have read so far its a bit complicated........ Soy is a goitregenic namely soy isoflavone genistein a compound which in effect inhibits/binds with iodine and interferes with the TPO process. By making the iodine useless and the thyroid work harder to produce T4/T3 and therefore needing more iodine..... in some cases the body responds by increasing in size by producing more follicles and swelling in size i.e. goitre. So therefore if you were iodine deficient.......you would still be iodine deficient..... (I think this may trigger an immune response.... Although this is just a theory I haven't found any evidence......)

    I'm still trying to put the pieces of this puzzle together. Links to studies if anyone has any.... I have some but need more!!

  • Thanks for this yodasbabe1. Complicated indeed!

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