A natural occurring trace mineral required for health.

Selenium is a trace element that is naturally present in many foods.



It is added to foods, and  is available as a dietary supplement. 


Some ready-to-eat breakfast cereals are fortified with selenium, and some fruits and vegetables contain selenium.



It is nutritionally essential.



It is a part of more than two dozen proteins that play critical roles in reproduction, thyroid hormone metabolism, DNA synthesis, and protection from oxidative damage and infection 


Selenium concentration are highest  in the thyroid gland than in any other organ.

Selenium has important functions in thyroid hormone synthesis and metabolism.

There is a relationship between selenium levels and thyroid gland function indicating an inverse relationship between serum selenium concentrations and thyroid volume, risk of goiter, and risk of thyroid tissue damage in women with mild iodine deficiency.

Trials of selenium supplementation in patients with thyroid disease have had varied results.

An essential nutrient for selenocysteine synthesis.

Selenocysteine is incorporated into a number of selenoproteins, most of which are enzymes which act as antioxidants.

It exists in two forms: inorganic and organic.



Both forms are good dietary sources of selenium.



Soils contain inorganic selenium  that plants accumulate and convert to organic forms.



Most selenium is in the form of selenomethionine, where it can be incorporated nonspecifically with the amino acid methionine in body proteins. 

Recommended dietary allowance is 55 mcg/d for individuals 14 years or older.

Selenium foods Include a variety of protein foods, including seafood, lean meats and poultry, eggs, legumes.nuts, seeds, and soy products. pork, beef, turkey, chicken, fish, shellfish, and eggs contain high amounts of selenium. 

Upper intake limits at 400 mcg/d.

Available in foods such as meat, grains, nuts and vegetables.

Supplementation to dietary intake usually not necessary.

Found in soil.

Toxicity associated with vomiting, nail discoloring, brittle nails, discolored nails, hair loss, fatigue, irritability, and foul breath (Fan AM).

A double-blind placebo-controlled trial of selenium supplementation is did not decrease the risk of secondary primary tumors of the lung or overall tumors, when administered with patients resected with stage I Non-Small Cell Carcinoma of the Lung (NSCLC) (Karp DD et al).

Beneficial for Hashimoto’s thyroiditis and Graves’ opthalmopathy.

Depleted plasma levels are associated with the excess mortality.

Selenium deficiency is very rare, and rarely causes overt illness.



The following groups are among those most likely to have inadequate intakes of selenium.



Even in low-selenium regions of the US, intakes are well above the RDA.



The lowest selenium intakes in the world are in certain parts of China, and the average selenium intake is low in some European countries, especially among populations consuming vegan diets.



Selenium levels are significantly lower in patients undergoing long-term hemodialysis, as it removes some selenium from the blood .



Heemodialysis patients are at risk of low dietary selenium intakes due to anorexia resulting from uremia and dietary restrictions.


Its deficiency could exacerbate iodine deficiency, and increase the risk of cretinism in infants 

Intravenous selenium in patients with severe sepsis does not improve outcomes (Bloos F et al.).

Selenium 60 mcg b.i.d. in a controlled study and comparing it to pentoxifylline , significantly improved quality of life, ocular involvement, and slowed progression of disease in mild Graves’ eye disease (Marcocci C et al).

In a study of over 58,000 men between the ages of 55 and 69, having a higher selenium level, as measured in toenails, reduced prostate cancer by 59%.

Because of its effects on DNA repair, apoptosis, and the endocrine and immune systems, its antioxidant properties, selenium might play a role in the prevention of cancer: an inverse association exists between selenium status and the risk of colorectal, prostate, lung, bladder, skin, esophageal, and gastric cancers.


In a Cochrane review of selenium and cancer prevention studies: the highest intake category had a 31% lower cancer risk and 45% lower cancer mortality risk as well as a 33% lower risk of bladder cancer and, in men, 22% lower risk of prostate cancer.

Selenium is not associated between selenium intake and risk of breast cancer. 

A meta-analysis of 20 epidemiologic studies showed a potential inverse association between toenail, serum, and plasma selenium levels and prostate cancer risk.


Nutritional Prevention of Cancer Trial in 1,312 U.S. adults with a history of basal cell or squamous cell carcinomas of the skin found that 200 mcg/day selenium for 6 years was associated with a 52% to 65% lower risk of prostate cancer.

The Selenium and Vitamin E Cancer Prevention Trial (SELECT), was discontinued after 5.5 years when analyses showed no association between supplementation with 200 mcg/day selenium with or without 400 international units (IU)/day vitamin E and prostate cancer risk.

Selenium levels are often low in people living with HIV: inadequate intake, excessive losses due to diarrhea, and malabsorption.



There is an association between lower selenium concentrations in people with HIV and an increased risk of cardiomyopathy, and death.



Lower selenium levels are associated in pregnant women HIV transmission to offspring and early death of offspring.



Selenium supplementation in adults with HIV can reduce the risk of hospitalization and prevent increases of HIV-1 viral load; preventing HIV-1 viral load progression can lead to increases in numbers of CD4 cells.



It is possible selenium supplementation in pregnant women can prevent early death in infants but has no effects on maternal viral load or CD4 counts.


Chronically high intakes of the organic and inorganic forms of selenium have are associated with a garlic odor in the breath and a metallic taste in the mouth, hair and nail loss or brittleness. 

Other symptoms of excess selenium include lesions of the skin and nervous system, nausea, diarrhea, skin rashes, mottled teeth, fatigue, irritability, and nervous system abnormalities.

Brazil nuts contain very high amounts of selenium, 68–91 mcg per nut.


Brazil nuts could cause selenium toxicity if consumed regularly. 


Acute selenium toxicity can cause severe gastrointestinal and neurological symptoms, acute respiratory distress syndrome, myocardial infarction, hair loss, muscle tenderness, tremors, lightheadedness, facial flushing, kidney failure, cardiac failure, and, in rare cases, death.


Data on the role of selenium in cardiovascular disease is conflicting.

Limited clinical-trial evidence does not support the use of selenium supplements for preventing heart disease, particularly in healthy people who already obtain sufficient selenium from food. 


Serum selenium concentrations decline with age: Deficient concentrations might be associated with age-related declines in brain function, possibly due to decreases in selenium’s antioxidant activity.

An analysis of NHANES data on 4,809 elderly people in the United States found no association between serum selenium levels (which ranged from lower than 11.3 to higher than 13.5 mcg/dL) and memory test scores.

In a systematic review that included nine placebo-controlled studies concluded that the available clinical evidence is insufficient to determine whether selenium supplements can prevent Alzheimer’s disease.


Tolerable Upper Intake Levels (ULs) for Selenium

Age Male Female Pregnancy Lactation

Birth to 6 months 45 mcg 45 mcg

7–12 months 60 mcg 60 mcg

1–3 years 90 mcg 90 mcg

4–8 years 150 mcg 150 mcg

9–13 years 280 mcg 280 mcg

14–18 years 400 mcg 400 mcg 400 mcg 400 mcg

19+ years 400 mcg 400 mcg 400 mcg 400 mcg



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