Iodine and your thyroid – when too much is not good for you
Your thyroid needs iodine to make thyroid hormones. When you have an issue with your thyroid, you may think that taking a supplement focused on supporting your health may be a great idea, right? Supplements like Metagenics’ Thyrosol, Solal’s Thyroplex, Thyrovive, and supplements that contain kelp.
Iodine is a tricky little thing. Think of it like Goldilocks: too little iodine, and you don’t feel well. Too much iodine? Well, you may trigger thyroid autoimmunity.
Here’s the research.
The Impact of Excess Iodine
Research shows that getting too much iodine can trigger autoimmune thyroid diseases, such as Hashimoto’s thyroiditis. Here’s what the studies have found:
- Higher Autoantibody Levels: In areas where people consume a lot of iodine, there’s a noticeable increase in thyroid autoantibodies—these markers indicate the immune system is attacking the thyroid. For instance, about 25% of people in regions with excessive iodine showed these markers compared to just 13% in iodine-deficient areas.
- Increased Risk After Iodine Supplementation: In some studies, when people who previously had low iodine intake suddenly increased their iodine levels (like through iodized salt), the prevalence of thyroid autoantibodies jumped significantly. One study found that 20% of healthy individuals developed signs of thyroid autoimmunity after taking a high dose of iodine.
- Animal Studies Support This: Research with animals has shown that adding extra iodine to their diet can worsen thyroid autoimmunity. This suggests that the same might happen in humans.
Countries with high and low levels of iodine intake
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, 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.
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. 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“.
The RDA (recommended daily allowance) for iodine is 15o mcg for adults (male and female). So check all your supplements and add up the iodine. Are you within the range, or are you moving towards 500 mcg?
So what should you do?
Be careful of not accidentally taking too much iodine, which may happen if you take thyroid support or kelp supplements. Salt is often iodized, so consider switching to non-iodized salt if you suspect your iodine-intake may be too high. Lastly, include food that naturally contain iodine, such as cod, shrimp, dairy, eggs, prunes and lima beans.
References:
- https://pmc.ncbi.nlm.nih.gov/articles/PMC3271310/
- https://www.healthline.com/nutrition/iodine-rich-foods
- https://pubmed.ncbi.nlm.nih.gov/33989173/
https://ods.od.nih.gov/factsheets/Iodine-HealthProfessional/
https://pmc.ncbi.nlm.nih.gov/articles/PMC8240726/