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Selenium Deficiency

Selenium is a mineral1 naturally found in soil and certain foods2. While our body doesn’t produce it, it plays an important role in our health, especially when it comes to our thyroid. It is found in foods like chicken, eggs, kidneys, liver, tuna, shellfish and Brazil nuts. Our small intestine absorbs it from our food and it’s transported to the liver before being disposed of through the urine and faeces.3


Food sources to counter selenium deficiency

Why do we need selenium?

Research has shown that selenium is an antioxidant4 and, while it is believed that too much can be toxic, it plays a major role in maintaining our health, including:5

    • helping to defend against viral infections

    • increasing blood flow and lowering heart disease risks

    • being a main part of the enzyme that helps the thyroid convert T4 to T36

This enzyme is also responsible for getting rid of hydrogen peroxide, a byproduct of thyroid hormone production. When selenium is low, a buildup of hydrogen peroxide may destroy thyroid cells over time.7

What causes selenium deficiency?

Until 2000 researchers believed that selenium deficiency contributed to thyroid conditions only when iodine levels were also low. However, a study published in the Biological Trace Element Research journal of that year presented a case of hypothyroidism caused entirely by lack of selenium.8  Another study9 noted a decrease in selenium levels in patients with autoimmune conditions, which could lead to or worsen inflammation. According to the study, getting enough selenium seems to help manage complications of autoimmune conditions and even improve symptoms, perhaps due to its anti-inflammatory effects.

Being deficient often comes down to three connecting factors: diet, geographical location and soil composition. In North America, for example, the soil is rich in selenium which means that crops have higher levels of it too. That’s why researchers believe most North Americans get enough selenium through their diet.

In her study, The importance of selenium to human health,7 Margaret Raymond found that the opposite was happening in the UK, where dietary consumption of selenium had dropped by 50% over two decades. This correlated to a reduction in imports of selenium-rich North American wheat in favour of European wheat.

What are the symptoms of a deficiency?

Selenium deficiency is known to cause problems for many systems of the body including the cardiovascular system, the immune system and the endocrine system. Many of the symptoms are therefore the same as those of an underactive thyroid:10,11

    • hair loss or changes to hair and nails

    • fatigue

    • brain fog, difficulty concentrating or memory problems

    • muscle weakness and pain

    • a weakened immune system, such as susceptibility to colds

    • male infertility

Testing for a deficiency

People at risk of a deficiency are those living in regions where soil or crops are selenium-deficient, those undergoing kidney dialysis and people living with HIV. Testing selenium levels alone can be difficult, especially in the UK where it’s not typically offered. However, you can request a blood test that looks at the amount in the serum/plasma of the blood.13

Order private blood tests, including selenium and other nutritional markers, from Thyroid UK’s partners.

Treatment and prognosis

When treating a selenium deficiency the NHS recommends 0.060mg (60 mcg) a day for women (19-64 years) and 0.075mg (75 mcg) a day for men (19-64 years).2 However, healthcare practitioners often treat with higher doses to allow for an optimal level.

Side effects of too much selenium can include hair loss or alopecia, damage to fingernails, nausea, change in bowel movements and problems to the nervous system.12

Experts agree that you should be able to get enough selenium from your diet alone. A single Brazil nut, for example, provides about 80 mcg.

Research has shown that supplementing can have a positive effect on plasma cholesterol and triglycerides levels.13  However, before supplementing, it’s a good idea to speak with your GP or a nutritionist if you suspect a deficiency. has a good article “Do Selenium Supplements Have Benefits? 19 Research Papers Examined” if you want to read further about selenium. 

For more support check out our online community:


  1. The effect of selenium supplementation on coronary heart disease: A systematic review and meta-analysis of randomized controlled trials
    J Trace Elem Med Biol.2017 Dec;44:8-16 Ju WLi XLi ZWu GRFu XFYang XMZhang XQGao XB
  2. Vitamins and Minerals
  3. Selenium
    Bioactive Food as Dietary Interventions for the Aging Population, 2013
  4. Selenium
    John D. Mark MD
    Integrative Medicine (Fourth Edition), 2018
  5. Thyroid hormone status in patients with severe selenium deficiency
    Kawai MShoji YOnuma SEtani YIda S
  6. Selenium and Thyroid Disease: From Pathophysiology to Treatment
    Mara VenturaMiguel MeloFrancisco Carrilho
    Clin Pediatr Endocrinol.2018;27(2):67-74
  7. The Importance of Selenium to Human Health
    Margaret P. Rayman Centre for Nutrition and Food Safety, School of Biological Sciences University of Surrey
  1. Selenium deficiency and hypothyroidism
    Antonio Pizzulli,  Alireza Ranjbar
    Biological Trace Element Research
    December 2000, Volume 77, Issue 3, pp 199–208
  2. Selenium and autoimmune diseases: a review article
    Sahebari MRezaieyazdi ZKhodashahi M
    Curr Rheumatol Rev.2018 Oct 16
  3. Selenium Deficiency
    Aparna P. Shreenath; Jennifer Dooley
  4. Selenium – Factsheets for Consumers
    National Institutes of Health
  5. Selenium
  6. Effect of Selenium Supplementation on Lipid Profile: A Systematic Review and Meta-Analysis
    Ju WLi XLi ZWu GRFu XFYang XMZhang XQGao XB
    J Trace Elem Med Biol.2017 Dec;44:8-16


Date updated: 17.08.21(V1.3)
Review date: 07.02.22

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