Should you take iodine if you have an underactive thyroid?

One the first things I learned when I was diagnosed with an underactive thyroid, is that the thyroid gland needs the mineral iodine to make thyroid hormones.  So the “logical” conclusion is that if you take a supplement with iodine in, surely your thyroid gland will make more thyroid hormones.  

But unfortunately, this is not necessarily how it works.  In fact, you could actually do more harm than good by taking an iodine supplement, especially if you have the autoimmune thyroid disease, Hashimoto’s Thyroiditis.  

So here is what you need to know about iodine before you start supplementing with it.  

The thyroid needs iodine

Iodine is like a special ingredient that the thyroid gland needs to make the thyroid hormones that help regulate your body’s processes and keep everything running smoothly.  The two main thyroid hormones are T4 (also known as thyroxine, and it is 4 iodine molecules) and T3 (also known as triiodothyronine, and it has 3 iodine molecules).

It gets iodine from the food we eat, as the body cannot produce iodine.

The thyroid gland then takes the iodine from the food we have eaten and combines it with an amino acid (a protein called tyrosine) to make the thyroid hormones. There is an enzyme called TPO (thyroid peroxidase) which plays an important role in this process.

This is where it is believed that iodine can be beneficial, as iodine stimulates the production of the TPO enzyme, which should then increase the levels of thyroid hormones.  Right?  Maybe not. 


The thyroid gland needs just the right amount of iodine

In his book The Thyroid Reset Diet, Dr Alan Christianson stated that the thyroid only needs a tiny amount of iodine, and the safe range (the range between low and high levels) is very narrow for iodine.  

When I think of iodine, I think of the story of Goldilocks.  Iodine mustn’t be too low, it mustn’t be too high, it needs to be just right!

If you don’t have enough iodine, then your thyroid cannot produce thyroid hormones.

But, if you have too much iodine, that is also not good.   So what is the issue here?  As Dr Christianson stated, “your thyroid can get rid of excess iodine only by producing thyroid hormones.  Yet, at the same time, excess iodine slows down the production of those thyroid hormones” (1).  

So, you want just the right amount, not too much, not too little.  

Could an iodine-deficiency be the cause of your hypothyrodism?

Iodine-deficiency could be the cause of your hypothyroid symptoms.  But before you reach out for the iodine and kelp supplements, let’s have a look at the latest status of iodine levels per country.  

In 1990 the World Health Organization categorised 112 countries as being “severely iodine-deficient.  Action was taken by global organisations, and in particular, iodized salt programs where done on a global level.  So what has happened since then?

A study published in 2021 in the European Journal of Endocrinology (2), showed that the number of countries with adequate iodine intake was 118, with 13 countries having “excessive intakes”.   However, 21 countries remained iodine deficient – countries such as Madagascar, Vietnam, Cambodia, Sudan, Iraq and Burkina, to name a few.  Interestingly, there were a few countries with very strong health systems  and otherwise successful public health programs where the iodine intake was also found to be inadequate, namely Norway, Germany and Finland.  

Some of the 13 countries with excessive iodine intake were Cameroon, Trinidad and Tobago, Costa Rica and Nepal, to name a few.  

So, unless you live in one of the countries with an “inadequate intake of iodine”, I would be careful before supplementing with iodine and recommend you speak with your licensed medical doctor first to see if it is the right supplement for you. 

It is more likely that there are other causes for your hypothyroid symptoms, such as the autoimmune disease Hashimoto’s Thyroiditis.  

What happens if you take iodine when you have Hashimoto's?

When you have the autoimmune disease Hashimoto’s Thyroiditis, it means that you have antibodies present in your blood.  TPO antibodies are antibodies to the enzyme TPO, which is needed in the process of making thyroid hormones.  

In his book “Why do I still have thyroid symptoms when my lab tests are normal?”, Dr Datis Kharrazian stated that supplementing with iodine when you have Hashimoto’s “is like throwing gasoline onto a fire.  Because iodine stimulates production of TPO, this in turn increases the levels of TPO antibodies dramatically, indicating an autoimmune flare-up.” (3)


A warning against excess iodine ingestion

The American Thyroid Association issued a statement in 2013 advising against the ingestion of iodine and kelp supplements in excess of 500 mcg iodine daily (4).  While iodine is required for normal thyroid function, excess iodine intake is not recommended and “may cause thyroid dysfunction.

The ATA stated that for most people, their “diet generally contains enough iodine to meet nutritional needs, with common sources being iodized salt, dairy products, breads, and seafood“.

In closing

Your thyroid needs iodine to make thyroid hormones.  We have to remember that it actually needs just a tiny amount, and the range for safe iodine levels is actually very small.  

Too little iodine is a problem, and so is too much iodine.  There are still a few countries where iodine deficiency is a problem, but 118 countries have more than adequate or even excess levels of iodine intake.

So before you start taking any supplements that includes iodine and kelp, I recommended that you speak with your licensed medical doctor first.  You may just need to make some dietary adjustments first to get the optimal level of iodine right.  


  1. The Thyroid Reset Diet, Alan Christianson,2021. Introduction.
  2. GLOBAL ENDOCRINOLOGY: Global perspectives in endocrinology: coverage of iodized salt programs and iodine status in 2020.  Zimmerman MB, Anderson M. , accessed 25 May 2023.
  3. Why do I still have thyroid symptoms when my lab tests are normal?”. Dr Datis Kharrazian, p 27.
  4. American Thyroid Association (ATA) Issues Statement On The Potential Risks Of Excess Iodine Ingestion And Exposure, 5 June 2023.  Accessed 25 May 2023.
Adele du Rand

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