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What Is Selenium: Signs You Have a Deficiency

Sarah Vordermeier

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What is selenium? Selenium is a versatile mineral that is essential for our immune system and thyroid gland. Not only a selenium deficiency but also an excess of selenium can pose a great threat our health. The good news is that just one Brazil nut a day can provide you with a sufficient amount of selenium.

A deficiency will negatively affect you both physically and psychologically. But too much selenium, as already mentioned, is also unhealthy and can even be life-threatening.

In this article, you will learn about foods with selenium that you can incorporate into your daily diet in order to reach your daily selenium requirement. Not only this – you’ll find out about selenium deficiency symptoms or, conversely, signs that your selenium intake is too high. We’ll also explore the dangers of selenium supplements if you do not take the right dosage – so read on!

What Is Selenium?

Selenium is an essential trace element, which means that it can only be absorbed through foods with selenium, and you only need a small amount of it. The human body stores 13 to 30 milligrams of selenium, the majority of which is deposited in the muscles and thyroid gland.[1]

The element selenium was discovered in 1817 and named after the Greek moon goddess Selene. A total of 200 years later, researchers have still not fully explored the potential of the trace element. Selenium influences vital processes that occur throughout our entire body – namely, in our immune system, nervous system, muscles, and thyroid gland. 

Did you know that when metal containing selenium is burned, a radish-like smell is created?[2]

What Does Selenium Do?

Selenium forms important proteins, which boost our immune system and prevent cell damage. It reinforces the function of both vitamin E and vitamin C as immunity-boosting vitamins. Moreover, together with iodine, selenium produces thyroid hormones, which boost sperm production and maintain nervous system function. Without selenium, the liver and pancreas would not be able to perform their digestive and blood sugar functions.[3, 4]

Selenium can help bind the heavy metal lead when there is too much of it in our bodies. A heavy metal in bound form can no longer pose a threat to the body and can be excreted more easily.[5]

What Is Selenium Deficiency?

The soil in Europe and in some parts of the United Stateshas lost a lot of selenium content over the years. Climate change is supposed to be to blame for this, as it promotes extreme weather conditions. The result is that heavy rainfall washes the selenium out of the soil, and prolonged dry periods also reduce the selenium content.

If there is too little selenium in the soil, it cannot accumulate sufficiently in plants, making food less selenium-rich.[9, 10] According to the National Institutes of Health, people in the United States generally consume sufficient amounts of selenium through their diet and supplements.[27]

Did you know that the soil with the highest selenium content is located in Nebraska? The soil in China, on the other hand, has a low selenium content.[1]

Who Is Most Affected by Selenium Deficiency?

Apart from people who eat a diet low in selenium, a deficiency can occur in the following groups:[12, 13]

  • Smokers
  • Alcoholics
  • Women who breastfeed
  • People suffering from intestinal diseases (as selenium cannot enter the bloodstream)
  • Dialysis patients (as a lot of selenium is lost during blood purification)

What Are Typical Selenium Deficiency Symptoms?

Because selenium influences processes in almost every part of our bodies, people with low levels of selenium might experience the following selenium deficiency symptoms:[11, 14]


Generic Complaints

Muscle weakness and joint pain
Impaired sperm production

Psychological Complaints

Depressive moods and mood swings

Organ Complaints

Thyroid and heart muscle disease
Liver disorders

Food with Selenium: What Should I Eat?

Both animal products and plant-based foods can provide us with sufficient selenium. The amount of selenium found in plant-based foods also depends on where they were cultivated and how selenium-rich the soil was. No food contains as much selenium as coconuts and Brazil nuts. It only takes one Brazil nut a day to satisfy your daily selenium requirement.[7]

Other foods with selenium content include:[8]

Foods with Selenium

Micrograms per 100 grams



Wheat bran

60 to 130



Brussels sprouts


White beans


Swiss cheese


The 6 best sources for selenium

How Do You Test Selenium?

Whether or not your selenium levels are optimal, this can be easily determined with a blood sample for a selenium blood test. If you or your doctor suspect selenium poisoning, a urine sample can provide clarity. Researchers are also trying to determine the status of selenium using hair and nail analyses. These methods are currently considered inappropriate, however, because the results vary too greatly.[21]

Which Selenium Supplement Is Best?

A total of 270 out of 1,073 people – that’s around one in four – stated in a survey on dietary supplements that they were taking selenium supplements. The right supplements can help you optimize your selenium levels, but there are a few things to be aware of.[15]

A good selenium supplement should contain selenomethionine. The body can absorb 90 percent of this selenium compound. Other selenium compounds such as sodium selenite or sodium selenate can only be absorbed to a limited extent.[1]

According to US recommendations, men and women over the age of 19 should consume 55 micrograms of selenium per day[27] Breastfeeding women need to increase their selenium intake to 70 micrograms to provide their infant with sufficient selenium via their breast milk. To read more about the ideal diet during pregnancy and breastfeeding, visit our Health Portal article, which answers commonly asked questions.

Are Selenium Supplements Safe?

Selenium only benefits your health when you take the right dosage. Thus, a daily intake of more than 300 micrograms of selenium through dietary supplements can lead to the following health issues:[12, 16]

  • Fatigue
  • Hair loss, discoloration of the skin
  • Nausea, vomiting, diarrhea
  • Bad breath (garlic breath)
  • Motor function disorders

If your selenium levels are too high over a longer period of time, your risk of type 2 diabetes and even prostate cancer may increase.[3]

Can You Take Selenium with Vitamin E?

Selenium and vitamin E mutually strengthen one another. You will often find recommendations online that state you need to take both nutrients at the same time. However, the German Society for Endocrinology has recommended avoiding combined selenium and vitamin E supplements. 

If you unknowingly are deficient in selenium, increasing your vitamin E intake can increase the risk of prostate cancer in men. You should only take combination supplements after discussing this with a physician. In a study published in the Journal of the National Cancer Institute, researchers observed that the risk was increased by 111 percent.[17–19]

Whether selenium and zinc should also be taken at the same time is still not clear. In a study involving rats, researchers were able to observe a negative effect on the prostate when taking selenium and zinc at the same time.[20]

How Are Selenium and the Thyroid Linked?

Our thyroid could not function properly without selenium. Can taking additional selenium help with thyroid problems?

It is not yet clear whether selenium is effective against thyroid diseases such as Hashimoto’s. In one study, pregnant women used selenium, which had a positive effect on hypothyroidism and Hashimoto’s after birth. People with endocrine orbitopathy might also see their symptoms improve with selenium supplementation.[22-24]

In endocrine orbitopathy, the eyeballs protrude significantly. The cause of this is an autoimmune reaction where the immune system attacks the body – in this case, tissue in the eye socket. Many of those affected also suffer from hyperthyroidism.[25]

What Is Selenium – at a Glance

What Is Selenium?

Selenium is an essential trace element that is stored primarily in the muscles and thyroid gland.

What Does Selenium Do?

This trace element supports immune and thyroid functions as well as male fertility.

What Is the Daily Selenium Requirement?

Adults should consume around 55 micrograms of selenium per day. You can reach your daily selenium requirement with just one Brazil nut.

What Are Typical Selenium Deficiency Symptoms?

Possible selenium deficiency symptoms include fatigue, depressive moods, increased susceptibility to infections, and thyroid problems.

Which Selenium Supplement Is Best?

Supplements containing the compound selenomethionine are best absorbed by the body. Do not use a combination of selenium and vitamin E, as vitamin E may increase the risk of prostate cancer in men if there is no selenium deficiency present. The risk of cancer may also increase if you take additional selenium supplements when your selenium levels are optimal. Selenium poisoning can lead to bad breath, hair loss, and yellow skin.


  1. ‘What is Selenium?’ American Nutrition Association, available at
  2. ‘Chemistry International -- Newsmagazine for IUPAC,’ available at
  3. Rayman M. P. ‘The importance of selenium to human health’, Lancet, vol. 356, pp. 233–241, 2000, doi:10.1016/S0140-6736(00)02490-9.
  4. Elmadfa I. Ernährungslehre, Verlag Eugen Ulmer Stuttgart, 2015
  5. Bjørklund G. ‘Selenium as an antidote in the treatment of mercury intoxication’, Biometals, vol. 28, pp. 605–614, 2015, doi:10.1007/s10534-015-9857-5.
  6. ‘Selen’, available at
  7. ‘Paranuss - Lebensmittel-Warenkunde’, available at
  8. ‘Lebensmittel’, DocMedicus Vitalstofflexikon, available at
  9. ‘Selen - ein guter Schutz für unseren Körper’, available at
  10. ‘Selenmangel nimmt zu: Klimawandel hat Einfluss auf unser Essen’, available at
  11. ‘Ausgewählte Fragen und Antworten zu Selen’, available at
  12. Die ganze Welt der Vitamine, Mineralstoffe und Enzyme, garant Verlag GmbH, Renningen, 2016
  13. Selen und Human-Biomitoring Stellungnahme der Kommission ‘Human-Biomonitoring’ des Umweltbundesamtes, available at
  14. Benton D., Cook R. ‘The impact of selenium supplementation on mood’, Biol. Psychiatry, vol. 29, pp. 1092–1098, 1991
  15. ‘Nahrungsergänzungsmittel’, available at
  16. Barceloux D. G. ‘Selenium’, J. Toxicol. Clin. Toxicol. vol. 37, pp. 145–172, 1999
  17. ‘Selen und Vitamin E nur bei Mangel,’ available at
  18. ‘Selen und Vitamin E’, available at
  19. ‘Selenium and Vitamin E Cancer Prevention Trial (SELECT): Questions and Answers,’ available at
  20. Daragó A., Sapota A., Nasiadek M., Klimczak M., Kilanowicz A. ‘The Effect of Zinc and Selenium Supplementation Mode on Their Bioavailability in the Rat Prostate. Should Administration Be Joint or Separate?’ Nutrients. vol. 8, 2016. doi:10.3390/nu8100601
  21. ‘Problematik, Klinik und Beispiele der Spurenelementvergiftung - Selen’, available at
  22. van Zuuren E. J., Albusta A. Y., Fedorowicz Z., Carter B., Pijl H. ‘Selenium supplementation for Hashimoto’s thyroiditis’, Cochrane Database Syst Rev. CD010223, 2013, doi:10.1002/14651858.CD010223.pub2.
  23. Ventura M., Melo M., Carrilho F. ‘Selenium and Thyroid Disease: From Pathophysiology to Treatment’, Int J Endocrinol. 2017,  doi:10.1155/2017/1297658
  24. Drutel A., Archambeaud F., Caron P. ‘Selenium and the thyroid gland: more good news for clinicians’, Clin. Endocrinol. (Oxf). vol. 78, pp. 155–164, 2013, doi:10.1111/cen.12066.
  25. ‘Pschyrembel Online | endokrine Orbitopathie’, available at
  26. ‘Others: vitamins and minerals’ National Health Service, available at, accessed on 23 November 2021.
  27. ‘Selenium: Fact Sheet for Health Professionals,’ National Institutes of Health, available at,is%20120.8%20mcg%20%5B15%5D, accessed on November 25, 2021.

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