Selenium- What’s that? What’s it good for?

by thyroid patient Cheryl Alvey

In 1969, the Apollo mission brought back to Earth samples of moon dust. Contained in those samples was selenium. Maybe then, it is no coincidence that the word selenium has its roots in the Greek word, selene, which means “moon.” However, it wasn’t until the early 80’s that the scientific community began to study selenium and its effects on the body. Scientists, within the last decade, are beginning to understand just how vital selenium is to immune response and thyroid functioning. The overall conclusion is that selenium is a dynamic and essential component of proper growth, development, immune function, and metabolism.

How do our bodies get selenium?Selenium is not a naturally occurring substance within the body but a trace mineral found in our foods and soil. And how much we get from our food is dependent on where the food grew. The amount of selenium in soils around the world varies. For the United States for example, you can view the soil levels of selenium here.

How do our bodies utilize the dietary selenium? To truly understand the importance of selenium and its inter-connectedness with the thyroid, as well as the immune system, it is necessary to understand how selenium is utilized from our dietary intakes. It’s synthesized into seleno-enzymes (or selenoproteins as the terms are inter-changeable). When the body synthesizes selenium, it is converted into one of three types of selenoproteins.

  • GPx (gluthiaone peroxidases) are anti-oxidants and, for this reason, are probably the best-known selenoproteins.
  • TRx (thioredoxin reductases) are active in cell structure and growth.
  • DIs (Iodothyronine deiodinases) are responsible for metabolic functions and the conversion of T4 to T3.

Each of these selenoproteins types has a role in thyroid function. In fact, there are 11 selenoproteins involved with the thyroid and thyroid hormone production. Therefore, it comes as no surprise that the selenium content of the thyroid is higher than that of any other body part. During times of selenium deficiency, the body will use any available selenium for the thyroid. This helps to explain the common symptoms of brain fog, senility, and overall decreased cognitive functions in those who are selenium deficient. Even the brain and neurotransmitters “take a back seat” to the functioning of the thyroid in regards to selenium status within the body.

What does selenium do for the thyroid? How is it connected to iodine?As stated earlier, selenoproteins in the Dis family convert the storage hormone T4 into the active T3 hormone. It does this by removing one iodine atom from the T4. But, selenium has other relationships with iodine as well. It is well documented that a severe iodine deficiency leads to neurological and myxedematous cretinism. It is only when a severe selenium deficiency is coupled with a severe iodine deficiency does the latter occur. Iodine deficiency also causes goiter but a selenium deficiency results in a “weighty” or heavy thyroid as evidenced by ultrasound results. Studies show that selenium protects against goiter and iodine is proving to protect against a heavy thyroid.

When there is an iodine deficiency and attempts to supplement with selenium occur, the selenium will magnify the iodine deficiency causing it to become worse. The reverse is also true. If there is a selenium deficiency and attempts are made to supplement with iodine, the iodine will exacerbate the selenium deficiency causing it to worsen as well. In fact, anytime one is high and the other is low, symptoms will occur and often times get worse. If there is a deficiency, both must be supplemented or kept low.

In addition to its affiliation with iodine, selenium is responsible for other regulatory functions within the thyroid. Selenium deficiency leads to the exacerbation of Graves, Hypothyroidism, Hashimoto’s and other thyroid disorders. Recent studies have shown that selenium supplementation can reduce serum levels of T4, Free T4, and Reverse T3 (See links below). To explain, the thyroid produces hydrogen peroxide during the production of T4. While some hydrogen peroxide is essential for proper functioning, excessive amounts of it can lead to high T4 production which results in a lower T3 availability. Too much hydrogen peroxide will also cause cell destruction. Selenium as GPx anti-oxidant breaks down excessive hydrogen peroxide and as a TRx prevents cell damage and necrosis of thyrocytes.

Can I take iodine if I have Hashi’s? What role does selenium play in this?Current research is proving that those with Auto-Immune Thyroiditis (AIT), which is widely known as Hashimoto’s Thyroiditis, or simply,Hashimoto’s, can and should supplement with iodine. Previously, those with AIT discontinued or avoided iodine because of the adverse effects it can have on the thyroid. However, the mechanisms of how and why the side effects of iodine supplementation occur are now largely understood. The thyroid must have iodine in order to make necessary hormones so those with AIT were often left with a dilemma. Take iodine and suffer side effects or don’t take iodine and continue to feel lethargic and listless. Current research extols that selenium restores the balance, not only of the thyroid, but also the immune system as well.

It is not uncommon for those with AIT to be selenium deficient due to their diets or other autoimmune conditions they may have (such as Celiac’s, Crohn’s, or Ulcerative Colitis). 90% of the body’s immune system resides in the small intestine where these autoimmune disorders are seated. So those with autoimmune disorders often avoid gluten as it intensifies the immune response. Unfortunately, most selenium is taken in from bread, pasta, grains, and flour enriched with selenium. All those who have gone gluten free avoid these foods due to the immune system’s response to the gluten. Furthermore, the majority of selenium is absorbed in the small intestine, so those with autoimmune issues are at a higher risk of Selenium deficiency.

Research has shown that selenium is an immune-modulator and a deficiency results in a compromised immune system. A mild selenium deficiency complicates AIT, but a severe deficiency in the mineral leads to thyrocyte destruction and the increase of macrophages – a type of white blood cell. Since selenium is responsible for modifying the body’s inflammatory response, it is a wise decision to add a dietary selenium supplement.

How much selenium can I take? Can it reduce antibodies? The vast majority of experts agree that a good starting therapeutic dose of 200 micrograms (mcg) has positive effects on both the thyroid and the immune system. At this dose, selenium significantly reduces TPO and TgAb antibodies; up to 55-86% and 35-92% respectively. Attainment of euthyroid status (after long term therapeutic dosing) has also been reported. It is important to note that selenium supplementation, even in those with a sufficient selenium level, will still enhance immune and thyroid response. Research data shows that a dose of less than 200mcg is not sufficient and will heighten iodine deficiency, goiter, and AIT attacks.

TheNational Institutes of Health Office of Dietary Supplementsstates thatadults should not consume more than 400 mcg of selenium per day.

What are good selenium-rich foods? What about supplements? When supplementing with selenium, several factors need to be kept in mind. Selenium is available through food as well as many over the counter supplements. Foods rich in selenium include shellfish, crab, kidney, liver, and Brazil nuts. It is important to remember that selenium rich food is only so if it is grown or raised in a selenium rich environment. Brazil nuts, touted as one of the best sources of selenium, vary in selenium content, as some grow in selenium poor soil. It is also more difficult to determine the amount of selenium being consumed through food intake, whereas over-the-counter supplements erase this uncertainty.

Supplements are a great way to ensure proper selenium intake, but there are differences among them. Selenium comes in many forms. Most selenium supplements are selenium yeast, selenomethionine, selenite and selenate. Selenite and selenate are both inorganic forms of selenium and have an absorption rate of about 50%. This unfortunately, increases the chance of selenium toxicity. For this reason alone, organic forms of selenium, such as selenium yeast or selenomethionine, are safer and are more readily absorbed. In fact, organic forms of selenium are the only way to raise serum levels of selenium within the body. This is attributed to their bioavailability. When using organic forms of selenium, current research shows that doses up to 1600 mcg a day were well tolerated with no signs of toxicity although most experts recommend upper tolerable limits to be 400-600 mcg a day. Selenium yeast does have a higher absorption rate, (about 60-70%), than that of selenite or selenate. Yet some manufacturers simply add inorganic selenium to yeast products, so caution is necessary when taking such products. In addition, those with candida issues may want to avoid yeast type supplements as their specific symptoms could be compounded. Of the selenium supplements, selenomethionine has the best bioavailability with an absorption rate of 90%. It is organic and yeast free. When compared with other selenium supplements selenomethionine proves to be the most applicable and safest for long-term therapeutic use.

Should I take selenium even if I’m not deficient or don’t have a thyroid issue? Again, selenium supplementation is not restricted to those with selenium deficient status, thyroid disorders, or the immune-compromised. Therapeutic levels help the young and the old alike even those with “normal” selenium levels. Selenium is a necessary component for healthy reproductive status and it aids in normalizing both testosterone and estrogen levels. Selenium aids in the removal of lipids and phospholipids. Excess amounts of these are responsible for high cholesterol levels; something those with thyroid disorders often have. A low selenium status is also indicated in those who struggle with depression and mood disorders. And, finally, selenium has been proven a powerful anti-carcinogenic supplement inhibiting cancer cells and reducing the risk of several cancers including prostate, breast, and uterine cancers.

The beneficial nature of selenium supplementation cannot be underscored. For most, 200-400mcg of selenium will prove to be sufficient. Those with amalgam fillings or those supplementing with iodine may need more. As with most supplements, selenium can have toxic effects when used in excess. Symptoms of selenium toxicity include diarrhea, hair loss, brittle nails, and other gastro-intestinal upset. To reduce the risk of toxicity it is recommended to start with 200mcg working toward the upper tolerable limits of 400-600mcg of organic selenium. Careful and proper supplementation with selenium is a wise decision for those who suffer thyroid and auto-immune disorders as it works to correct imbalances in thyroid functioning and immune response.

Cheryl is a wife, mother, daughter, poet, writer, and has hypothyroidism. She began researching alternative methods and treatments for hypothyroidism when her doctors told her nothing was wrong with her because her TSH was normal. After struggling for over ten years, Cheryl is now on optimal treatment and using her writing and research abilities to help others who are still looking for answers


Here’s a study that showed selenium did NOT cause a rise in RT3, and in fact, lowered it:

In fact, there are studies here which show that LOW levels of selenium can result in increased RT3:

This medical book states that tho RT3 comes from T4, it concludes thatlow selenium increases RT3:

i.e. the enzymes that convert T4 to T3 and convert T4 to RT3, are selenium dependent to do their job. But that doesn’t necessarily mean that selenium increases your RT3.