Skip to main content

Thyroid disease requires the right balance between iodine and selenium

- and selenium deficiencies are widespread

Thyroid disease requires the right balance between iodine and selenium An estimated 500,000 Danes suffer from some kind of thyroid disorder, the most common of which is Hashimoto’s disease, which slows down your metabolism. The formation and activation of thyroid hormones depend on iodine and selenium, and it is essential that the two nutrients are properly balanced. Having too little or too much iodine increases your risk of Hashimoto’s disease, and the same is the case with selenium, a nutrient that many people lack.
Some of the problems that are seen in people with slow metabolism are extreme fatigue, weight gain, constipation, cold sensitivity, swollen neck, and dry skin. The symptoms can vary, however, and many people still have not been given the proper diagnosis. Medical therapy with thyroid hormones will not necessarily solve the problem. In fact, as many as 20 percent of patients actually feel worse, although their blood tests appear to be normal. It is therefore important to focus more in the role of iodine and selenium in the metabolism.

Iodine is an essential trace element. It has been known for long that it is important for the thyroid gland, metabolism, energy turnover, and child growth. An iodine deficiency may cause goiter (enlarged thyroid gland) and thyroid disorders, just like children may develop cretinism, a special kind of stunted physical and mental development.
Iodine is mainly found in fish, shellfish, and seaweed, but soil conditions may also affect levels of the nutrient in the diet. In the 1920s, the Swiss army observed that men from alpine areas, where iodine levels in the soil were lower, were more prone to get goiter compared with the men from the western regions of the country. This meant that more men from the iodine-depleted alpine areas were unable to perform military service.
In 1922, Switzerland was the first country to introduce iodine-enriched table salt, and this reduced the rate of both goiter and cretinism. In addition, it helped even out the difference in height among people from different parts of the country.
In 1924, the United States also introduced a program with iodine-enriched table salt, which has especially helped reduce the rate of goiter in the iodine-deprived “goiter belt” that is placed in the Northwestern regions of the United States.

The iodine intake in Denmark is still borderline low

Until the 1990s, nobody suspected that there was iodine deficiency in Denmark, not until a high rate of goiter was detected in Jutland. This difference was because the iodine content in groundwater varied from one part of Denmark to another. Since year 2000, table salt manufactured in Denmark (with the exception of salt flakes) has been enriched with iodine to prevent goiter. However, even though the iodine intake has increased slightly, it is still not sufficient, especially among pregnant women.
It seems that iodine deficiency may be contributing to the increased rate of thyroid disorders, but a sudden increase in iodine intake may even be a problem for people who are prone to thyroid disease without knowing it, especially if they also lack selenium. We will address that later.

The thyroid gland needs iodine, but if you suddenly increase your iodine intake, it may cause problems, especially if you do not get enough selenium.

Why the thyroid gland and the thyroid hormones need iodine and selenium

The thyroid gland is located at the front of the neck and is activated by thyroid-stimulating hormone (TSH) that makes the thyroid gland produce hormones to stimulate cellular oxygen uptake. This affects the metabolism directly by enabling cells to metabolize calories into energy. The thyroid gland produces two different thyroid hormones. T4 is the passive hormone that contains four iodine atoms, while T3 is the active hormone that contains three iodine atoms. In order to activate the metabolism in the different cells and tissues of the body, special selenium-containing enzymes (deiodinase 1-3) remove an iodine atom from T4, thereby converting it into active T3 hormone. This process is carried out in accordance with the body’s need for T3.
If too little T3 hormone is produced, your metabolism slows down. An overproduction of T3, on the other hand, speeds your metabolism up. It is important that both iodine and selenium are present in the body to ensure that this regulation works properly.

Did you know that the thyroid gland is the organ in the body with the highest concentration of iodine and selenium?

Hashimoto’s disease (Hashimoto’s thyroiditis)

Hashimoto’s disease, which causes the metabolism to slow down, was described for the first time in 1912 by a Japanese doctor named Hakaru Hashimoto. It is an autoimmune disease where the immune system attacks the thyroid gland, causing inflammation and tissue destruction.
Hashimoto’s disease can be insidious, and it often starts with hyperthyroidism (increased metabolism). As the thyroid gland and its enzymes are gradually attacked by two different antibodies called thyroid peroxidase (TPO) and thyroglobulin (Tg), the production of T3 and T4 decreases. This makes the pituitary gland step up its TSH production in order to increase the production of thyroid hormones. However, because the thyroid gland is destroyed by inflammation caused by the overactive immune defense, it has no effect, and TSH levels continue to be elevated.
The low levels of thyroid hormone often lead to an increasing number of symptoms, depending on which tissues have the energy shortage. It is therefore always vital to get an early diagnosis and therapy, especially if you are pregnant.
Hashimoto’s disease is diagnosed by means of blood tests that look at the presence of the two antibodies, anti-TPO and anti-TG, plus TSH, free T4, free T3, and reverse T3.

Symptoms of hypothyroidism

  • Fatigue and poor concentration
  • Cold sensitivity
  • Slow heart rate and possibly tinnitus
  • Weight gain (in spite of reduced appetite)
  • Swollen neck/head
  • Sagging, dry skin, hair loss, and frayed nails
  • Constipation
  • Despair and a tendency to become depressed
  • Irregular periods
  • Goiter (enlarged thyroid gland)

Too little and too much iodine

As mentioned earlier, the thyroid gland needs iodine to make thyroid hormones. Normally, we humans tolerate iodine rather well, but it appears that patients with thyroid disorders such as Hashimoto’s disease should be careful not to get too much iodine, especially if they are selenium deficient. Hashimoto’s patients may feel better, if they take large quantities of iodine for a period, but after a few weeks, their condition may worsen. This was observed in a study that was published in Current Opinion in Endocrinology & Diabetes and Obesity in 2012.
A Chinese study from 2006 showed that a large intake of iodine increases the risk of autoimmune reactions in the thyroid gland, which is what you see in Hashimoto’s disease. Another Chinese study from 2014 that included 146 men and women with sub-clinically low metabolism showed that a lower intake of iodine led to decreased levels of thyroid-stimulating hormone (TSH), which is a sign that the thyroid gland is recovering.
Still, it is not enough to look at iodine intake only, as selenium plays a nearly equally important role in the metabolism, yet this nutrient is often overlooked.

Thyroid patients risk getting too much iodine by consuming large quantities of iodine-enriched salt or seaweed, or if they are exposed to radioactive iodine.

Selenium has different functions in the thyroid gland and metabolism

Selenium supports as many as 35 different selenoproteins, which are essential enzymes with an antioxidant function. Selenium is particularly important for the energy turnover, the cardiovascular system, the immune system, fertility, cancer prevention, and metabolism.
As mentioned before, the body needs the selenium-containing enzymes deiodinase 1-3 to convert the passive T4 hormone to the active T3 hormone in the body’s different tissues.
Other selenium-containing enzymes work as powerful GPX antioxidants (glutathione peroxidase) that protect the thyroid gland against free radical damage and oxidative stress. Free radicals are a byproduct of our natural oxygen turnover, and the free radical load is increased tremendously by infections, tobacco smoke, alcohol, medicine, exposure to mercury and other environmental pollutants, stress and ageing processes.
Because around five liters of blood flush through the thyroid gland every hour, it is particularly vulnerable to free radicals (that are found in the blood). Large quantities of free radicals may cause cellular damage and inflammation. We therefore need different antioxidants, and the GPX antioxidants are especially good at neutralizing free radicals and protecting the thyroid gland.
Selenoprotein S is a third type of selenoprotein that regulates inflammatory processes in the endoplasmic reticulum of the cells, which is important for a variety of cellular metabolic processes.
A Portuguese study from 2014 showed that a selenoprotein S deficiency is associated with increased presence of different cytokines that are involved in inflammation and Hashimoto’s disease.

Selenium appears to protect against too much iodine

It appears that having sufficient amounts of selenium in the body protects against too much iodine and against Hashimoto’s disease. In a Chinese study, scientists compared two geographical areas where people had different selenium intake. In the area where people got enough selenium, the rate of thyroid disorders was significantly lower. The researchers measured selenium levels in the blood and found a link between high selenium status and a lower risk of developing autoimmune diseases like Hashimoto’s.
In both areas, the Chinese had higher intake of iodine, which in itself may predispose to the development of Hashimoto’s disease, but this was not the case among the Chinese who had plenty of selenium in their blood. It appears that iodine and selenium must be in some kind of balance, and it is especially important to get enough selenium.

Selenium’s importance for the thyroid gland and the metabolism

  • Converts passive T4 to active T3 (deiodinase 1-3)
  • Works as an antioxidant by protecting against free radicals (GPX)
  • Controls inflammatory processes (selenoprotein S)

Our diet is low in selenium, but we can correct that problem

The selenium intake from European diets is far lower than what you get from diets in other parts of the world because of the low selenium content in our soils and dietary habits. This may contribute to thyroid disorders such as Hashimoto’s disease. However, by taking 100-200 micrograms of selenium daily as a supplement, it is possible to increase one’s selenium intake to match the high intake levels found in countries like Canada, USA, and Japan. Selenium yeast with a variety of different organic selenium species is the best, as this kind of supplement is very similar to the natural variety of selenium types that you get from eating a balanced diet with many different selenium sources.

Why does hormone therapy not work?

Hypothyroidism (slow metabolism) is normally treated medically with synthetic T4 hormone. If this type of treatment fails to work as expected, it may be a result of having too little selenium in the blood. This prevents a successful conversion of passive T4 hormone to active T3, a process that involves selenium-containing enzymes (deiodinase).

Will selenium become the new standard treatment?

Numerous international studies have demonstrated that daily supplementation with 200 micrograms of selenium has a positive effect on autoimmune thyroid disorders like Hashimoto’s disease (which causes the metabolism to slow down) and Graves’ disease (that speeds it up).
Two large Danish studies are currently investigating the effect of selenium supplements given to thyroid patients. One study (CATALYST) deals with Hashimoto’s patients, while the other study (GRASS) is carried out on Graves’ patients.
The patients receive 200 micrograms of organic selenium yeast daily. If the results of these studies turn out positive, selenium will be included as part of the standard treatment in the future. Doctors will also observe if the need for synthetic T4 decreases because selenium is able to both increase levels of thyroid hormone and lower levels of antibodies.

Other facts and useful tips

  • Iron and zinc are also important for your metabolism. However, iron supplements are only recommended for those who have a diagnosed deficiency
  • Have your metabolism measured by a doctor or endocrinologist if you suspect that it is either too active or too slow
  • If you have Hashimoto’s disease, you should look into whether you get too little or too much iodine
  • If you have Hashimoto’s disease, you should limit your intake of foods with goitrogens that can disrupt the thyroid gland’s ability to utilize iodine. The foods with most goitrogens are soy, tofu, peanuts, cabbage, and other cruciferous vegetables.
  • To prevent and treat Hashimoto’s, it is a good idea to take 100-200 micrograms of selenium yeast daily as a supplement
  • Hashimoto’s patients should also be tested for gluten intolerance (celiac disease), as there is a link between the two things


Greenhill, J.P. Reduction of Deafness and Dumbness in Switzerland as result of Goiter Prophylaxis with Iodized Salt. American Journal of Obstetrics and Gynecology. 1945

James Feyrer et al.. The cognitive Effects of Micronutrient Deficiency: Evidence from Salt Iodization in the United States. (2013)

Quian, M et al. The Effects of Iodine on Intelligence in Children: A Meta-analysis of Studies Conducted in China. Asia Pacific Journal of Clinical Nutrition. 2005

Joung, JY et al. Effect of Iodine Restriction on Thyroid Function in Subclinical Hypothyroid Patients in an Iodine-Replete Ares. A Long Period Observation in an Large Scale Cokort. Thyroid 2014

Weiping Teng et al. Effect of Iodine Intake on Thyroid Diseases in China. New England Journal of medicine 2006

Michael B Zimmermann et al. Iodine Deficiency and Thyroid Disorders. The Lancet Diabetes & Endocrinology 2015

Angela Leung et al. Iodine-induced Thyroid Dysfunction. Current Opinion in Endocrinology & Diabetes and Obesity. 2012

Susan J FairWeather-Tait et al. Selenium in Human Health and Disease. Antioxidant & Redox Signaling 2011

Drutel, A et al: Selenium and the thyroid gland: more good news for clinicians. Clinical Endocrinology 2013

Shomburg, Lutz: Selenium, selenoproteins and the thyroid gland: interactions in health and disease. Nat. Rev. Endocrinol 8, 2012

Liliana R Santos et al. A Polymorphism in the promotor Region of the Selenoprotein S Gene (SEPS1) Contributes to Hashimoto´s Thyroiditis Susceptibility. The Journal of Clinical Endocrinology & metabolism 2014

Qian Wu et al. Low Population Selenium Status is Associated With Increased Prevalence of Thyroid Disease. The Journal of Clinical Endocrinology & metabolism 2015.

Gärtner R et al: Selenium supplementation in patients with autoimmune thyroiditis decreases thyroid peroxidase antibodies concentration. J Clin Endocrinol Metab. 2002

The chronic autoimmune thyroiditis quantity of life serum trial (CATALYST): Study protocol for a randomized controlled trial

Selenium supplementation for patients with Graves’ hyperthyroidism (the GRASS trial): study protocol for a randomized controlled trial

EFSA (Den Europæiske Fødevaresikkerhedsautoritet)

Pernille Lund: Har du problemer med dit stofskifte? Ny Videnskab 2015

  • Created on .