Selenium

What is Selenium?

Selenium is an essential trace mineral needed by the body in small amounts to maintain health and wellbeing.

The name selenium comes form the Greek word selēnē which means ‘moon’ named after the moon Goddess in Greek mythology. The name selenium was coined by Swedish chemist Jöns Jacob Berzelius due to initial confusion with the similar element tellurium.

For optimal health t is important to obtain sufficient amounts of selenium through dietary intake and where necessary supplementation. Selenium has many functions in the body and works synergistically with other nutrients. It is an important part of glutathione peroxidase (GPX) which is an antioxidant complex or enzyme that helps to prevent oxidative damage (reduce peroxides), stabilize cell membranes and reduce platelet aggregation which can help to reduce risk of atherosclerosis.

Selenium is a cofactor for the enzyme lodothyronine deiodinase an important enzyme that helps convert T4 into T3 and T3 into T2. There are two organic forms of selenium known as selenomethionine and selenocysteine consisting of the two amino acids methionine and cysteine both of which contain sulfur. The inorganic forms of selenium are sodium selenite and sodium selenite. In the body the selenium is stored as selenomethionine.

The highest concentrations of selenium is found stored in the thyroid gland, kidney, liver, heart, pancreas, and the muscles.

Selenium is mostly excreted through urine and feces.[1]

Health Benefits of Selenium

May help prevent cancer

Higher rates of certain types of cancer are more common where the selenium amounts in soil is siginificantly low. Selenium deficiency has been linked to various forms of cancer such as skin, colorectal, prostate and lung cancer. Selenium is an antioxidant that helps protect against free radicals which are known to contribute to oxidative damage and increasing risk of various diseases. Some studies have shown selenium to have protective qualities against chemicals and UV rays which are linked to the development of cancer. Selenium also woks synergistically with vitamin E having very similar role in preventing free radicals. Both nutrients work together to induce apoptosis in abnormal cells. The two nutrients also work together to reduce iron overload. Excess iron has been linked to cancer. [2] [3] [4] [5] [6] [7]

Supports thyroid health

Selenium along with iodine plays a very important role in thyroid help supporting and maintaining its functions in the body. There are many interactions between selenium and iodine associated with thyroid health. Iodine is found concentrated mostly in the thyroid glands. Deiodinase enzymes (DI’s) which rely on selenium are involved in the conversion of the thyroid prohormone T4 (thyroxin) into the active hormone T3 (triiodothyronine). These important enzymes also help convert T3 into T2. The activation of T3 by Deiodinase enzymes occur in the liver and brain.

Cretinism (myxeodematous cretinism) is associated with selenium deficiency and or iodine deficiency.  

Deficiency of selenium is associated with impaired thyroid hormone metabolism and thyroid hormone function leading to thyroid conditions such as hypothyroidism.    In addition to iodine and selenium effects on the thyroid zinc also plays a part.

Selenium and iodine need to be balanced as both work synergistically on thyroid health. An imbalance where one nutrient is low and the other is high can lead to thyroid health issues. [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19]

Selenium supports hormone health

In addition to thyroid health selenium also plays an important role in estrogen and testosterone. Selenium is needed by the enzyme sulfotranserfase needed to break down estrogen. A deficiency of selenium can lead to estrogen dominance which can cause problems for the thyroid. It also causes an imbalance between progesterone and estrogen which need to be balanced for optimal health. Selenium is required in the synthesis of testosterone and works synergistically with vitamin E which also helps support production of hormones. [20] [21]

Selenium has antioxidant activity

Selenium is an important part of glutathione peroxidase (GPX / GSHPx) which is an antioxidant complex or enzyme that helps to prevent oxidative damage (reduce peroxides), stabilize cell membranes and reduce platelet aggregation which can help to reduce risk of atherosclerosis. As an important factor for GPX it also helps body lipids and fats from oxidizing. Selenium also helps protect the skin from UVA damage which causes oxidative stress and symptoms manifest on the skin as ‘age spots’ or ‘liver spots’. Some research have also shown that these symptoms are linked to similar spots of peroxidized fats in the liver revealed in autopsies. Some studies are also showing that maternal selenium deficiency can increase hydrogen peroxide leading to oxidative stress to the fetus.

Selenium also works together with vitamin E in reducing free radicals and preventing oxidative damage. These two nutrients have similar antioxidant activity and work synergistically. [22] [23] [24] [25] [26]

Prevents heart disease

Selenium dependent enzymes GPX and PHGPX have antioxidant properties which help protect from oxidative damage associated with heart disease. Studies are showing a link between selenium and heart disease. Studies have revealed that individuals with low levels of selenium have an increased risk of heart disease whereas those with sufficient levels of selenium have a reduced risk although more research is needed to understand the significance of selenium and its role in cardiovascular health. [27] [28]

Prevent inflammatory conditions

Low levels of selenium has been associated with arthritis. Prostaglandins which are lipid compounds and have hormone-like effects in the body can contribute to inflammation and lead to inflammatory diseases such as arthritis. Selenium deficiency as well as vitamin E are associated with higher prostaglandin production. People with arthritis have been shown to have low levels of selenium. [29] [30] [31]

Agonists

Vitamins: A, B1, B3, B6, B12, C, E

Minerals: Ca, Cu, Fe, K, Mn, Na, Zn, I

Other: Glutathione peroxidase (GPX), Iodothyronin Deiodinase (thyroid enzyme helps convert T4 to T3)

The antioxidant glutathione requires selenium-dependent enzyme glutathione peroxidase (GPX). Selenium is a cofactor for GPX

Selenium is a cofactor for the thyroid enzyme Iodothyronin Deiodinase

Selenium and iodine work synergistically for thyroid health.

High dietary intake of vitamin C can increase absorption and retention of sodium selenite. [32]

Vitamin C increases absorption of selenomethionine and organic selenium-containing yeasts. However vitamin C combined with inorganic selenium in the food converts to insoluble and bio-unavailable elemental selenium. High mega doses of vitamin C (ascorbic acid) may reduce absorption of selenium. [33]

Serum levels of selenium enhanced with vitamin D supplements. [34]

Selenium works synergistically with vitamin E and both have antioxidant activity which helps protect the body from oxidative damage caused by free radicals.

Selenium also works synergistically with vitamin E and have a role in the production of the male sex hormone testosterone.

Low levels of vitamin E may increase requirement of selenium.

Vitamin E can reduce harmful effects of selenium toxicity. [35] [36]

Selenium and vitamin E induce apoptosis. [37] [38]

Vitamin E and selenium work synergistically to help reduce effects of iron overload. [39]

Iodine and selenium work synergistically for thyroid hormone metabolism. Selenium is a cofactor for enzymes that help convert T4 to T3. [40]

Antagonists

Vitamins: A, B2

Minerals: Cu

Metals: Al, Cd, Hg

Other: Phytates (Phytic acid), organophoshorus pesticides, smoking, alcohol, birth control pills, hydrogenated polyunsaturated fats (PUFAs), heated / rancid PUFAs

Increase in dietary copper may reduce selenium absorption but dependent on low levels of selenium and may be avoided with higher selenium intake. [41]

Imbalance of selenium and copper ratio can lead to oxidative stress. [42]

Cadmium is a selenium antagonist. Smokers have been shown to have reduced levels of selenium. [43] [44]

Suggestions are made for fortifying cigarettes with selenium to provide safer tobacco products. [45]

Heavy metals such as aluminium, mercury and cadmium inhibits selenium absorption. [46]

Low vitamin E levels may increase requirement for selenium.

High sulfur intake which can be found in legumes or alliums may increase selenium requirements.

Organophoshorus pesticides reduces selenium levels [47]

Recommended Dietary Allowance

Age

Selenium: Adequate Intake (AI) in micrograms (mcg/d)

INFANTS

0-6 months

15 mcg

7-12 months

20 mcg

 

 

 

Age

Selenium: Recommended Dietary Allowance (RDA) in micrograms (mcg/d)

CHILDREN

1-3 years

20 mcg

4-8 years

30 mcg

 

 

 

Age

Selenium: Recommended Dietary Allowance (RDA) in micrograms (mcg/d)

MALES

9-13 years

40 mcg

 

 

14-18 years

55 mcg

 

 

19-30 years

55 mcg

 

 

31-50 years

55 mcg

 

 

51+ years

55 mcg

 

 

 

 

 

 

FEMALES

 

 

Pregnancy

Lactation

9-13 years

40 mcg

 

 

14-18 years

55 mcg

60 mcg

70 mcg

19-30 years

55 mcg

60 mcg

70 mcg

31-50 years

55 mcg

60 mcg

70 mcg

51+ years

55 mcg

 

 
         

 

Tolerable Upper Intake Level (UL) for selenium is set at or 400 mcg for healthy adults.

[48] [49] [50]

Food Sources of Selenium

Food sources of selenium include brazil nuts, brewer’s yeast, offal / organ meats (liver, kidneys), meat, pork, fish, shellfish, whole grains, brown rice, wheat germ, oat bran, sesame seeds, broccoli, cabbage, cucumbers, radishes, garlic, onions, torula yeast, molasses, dairy products, tuna, and kelp.

Research on trace minerals in beverages has shown selenium is contained in beer along with other trace minerals such as iodine, iron, fluorine, calcium and copper. [51] [52]

Selenium content in fruits and vegetables are very low and a poor source of the nutrient.

Selenium Supplementation

Selenium is available as tablets, capsules and in ionic liquid form. Selenium is available in organic form selenomethionine and inorganic form such as sodium selenite or sodium selenate. Selenomethione and selenium yeast are considered to be more bioavailable and better absorbed forms. L-selenomethionine is the form utilized by the body and is also available as a supplement. [53]

Deficiency Symptoms of Selenium

Signs and symptoms of selenium deficiency include:

  • Fatigue
  • Hair loss [54] [55]
  • Weight gain
  • Joint and muscle pain
  • Discoloration of nails
  • Discoloration of skin
  • Mental slowing
  • Depression
  • Low mood
  • Brain fog
  • Hypothyroidism
  • Hyperthyroidism
  • Kashin-beck disease
  • Keshen disease
  • Fertility problems
  • Recurrent miscarriage
  • Goiter
  • Cretinism
  • Weak immune system
  • Worsened asthma symptoms
  • High hepatic copper levels [56]
  • Anemia
  • Cardiomyopathy (sudden death in athletes)
  • Heart palpitations
  • Irregular heartbeat (rapid heartbeat)
  • Chemical and drug sensitivities

The following are some of the causes of selenium deficiency:

  • Smoking cigarettes
  • Excessive alcohol intake
  • Birth control pills
  • Low dietary selenium intake
  • Low soil selenium levels
  • Malabsorption
  • Long-term parenteral nutrition without selenium
  • Exposure to toxins and man-made chemicals (pesticides)
  • Heavy metal exposure (such as mercury)
  • Excess intake of vegetable oils

Cellular membranes are made up of fats which selenium can help protect from peroxidation. Peroxidation will reduce the cellular membrane from passing essential nutrients and these include a variety of vitamins and minerals. Selenium deficiency could potentially be an underlying cause for many other nutritional deficiencies.

*Selenium deficiency could potentially be exacerbated by the addition of high intake of vegetable oils. Hydrogenated polyunsaturated fats should be avoided as well as avoiding cooking with these oils as they can become rancid.

Various heavy metals such as mercury and lead can induce selenium deficiency. [57]

The following are some health conditions associated with a selenium deficiency:

  • Thyroid Eye Disease (TED), fibrosis [58] [59]
  • Lupus [60]
  • Multiple sclerosis – deficiency from childhood [61] [62] [63]
  • Impaired thyroid function [64] [65] [66] [67]
  • Thyroid cancer [68]
  • Keshan disease
  • Kashin-Beck disease [69]
  • Osteoarthritis [70]
  • Heart enlargement (cardiomyopathy)
  • Heart rhythm disturbance (cardiac dysrhythmia) [71]
  • Pulmonary edema
  • Cretinism (Associated with iodine and selenium deficiency) [72]
  • Liver cirrhosis
  • Pancreatitis,
  • Lou Gehrig's
  • Parkinson's diseases (mercury toxicity)
  • Alzheimer's Disease (high intake of vegetable oil)
  • Sudden infant death syndrome
  • Breathlessness in adults
  • Cancer
  • Anemia (sickle cell anemia)

Selenium levels can be checked through a blood test.

Toxicity Symptoms of Selenium

Selenium toxicity is unlikely through dietary intake unless soil levels are in too high and can occur through chronic intake of selenium supplements. Selenium toxicity is also likely from high intake of inorganic selenium. Signs and symptoms of selenium toxicity include:

  • Nausea
  • Vomiting
  • Fatigue
  • Irritability
  • Foul breath (“garlic breath”)
  • Skin rashes
  • Metallic taste in the mouth
  • Brittle hair
  • Hair loss
  • Nail discoloration
  • Brittle nails
  • Loss of nails
  • Joint pain
  • Fatigue
  • Peripheral Neuropathy
  • Tooth Decay
  • Nervous System Abnormalities
  • Mineral imbalance
  • Reduced zinc absorption
  • Selenosis
    • Decreased cognitive function
    • Weakness (muscle damage)
    • Liver damage
    • Paralysis
    • Death

Selenosis was discovered in miners and has been found in people taking excessive selenium supplements.[73]

Linseed meal (flaxseeds) has shown to protect chicks against selenosis. [74]

Precautions and warnings

It’s important to check with your doctor if you are taking any medications or have health conditions that may be affected by selenium before supplementing with selenium.