Selenium (Se) is a non metal chemical element with atomic number 34.

It is an essential trace element in humans.







Selenium is used to produce selenoproteins. 25 of these have been identified but the metabolic functions of only about 50% of these have been established.


The selenoproteins we understand are:

1. Glutathione Peroxidases

Glutathione is a simple molecule made by our bodies using three amino acids – cysteine, glycine and glutamine.  It is a powerful antioxidant and gets its power from sulfur groups that we ingest when we eat crucibles such as broccoli, cauliflower, brussels sprouts and cabbage.

Peroxidases are enzymes that catalyze the reduction of reactive oxygen species such as hydrogen peroxide into harmless molecules of water and oxygen or alcohols so that they are stopped from attacking and wrecking havoc on our cells.

 Glutathione peroxidases are antioxidant enzymes and five of them contain selenium.


 2. Thioredoxin Reductase:

Thioredoxin is a protein involved in the transfer of electrons and also plays a role in cell to cell communication.  Thioredoxin reductase is important for cell growth regulation and helps to regenerate some antioxidants which assist in this regulation.  Selenoproteins are part of thioredoxin reductase.


3. Iodothyroine deiodinases:

Three selenoproteins called iodothyroine deiodinases, can activate or inactivate the thyroid hormone making selenium essential for normal metabolism and growth as thyroid hormone controls both of these.


4. Selenoprotein P:

Found in our blood plasma it is a selenoprotein that transports the protein for selenium and acts as an antioxidant protecting the cells that line our blood vessels from free radical damage.


5. Selenophosphate synthetase:

Our genetic code directs the incorporation of the amino acid selenocysteine into a selenoprotein.  Selenophosphate synthetase is a selenoprotein itself that is used to catalyze this process. ( A ‘chicken or the egg’ kind of scenario!)


6. Methionine-R-sulfoxide reductase:

Initially identified as selenoprotein R or X by two different laboratories is involved with thioredoxin reductase which as stated above is important for cell growth regulation and cell signalling.


7. kDA selenoprotein aka Sep 15:

Operating in the endoplasmic reticulum of every cell in our bodies this protein is involved in protein folding. Every type of protein is folded differently in order to perform its assigned function. Therefore Sep 15 supports the proper functioning of proteins.

It is also involved in redox reactions (the transfer of electrons from one type of oxygen containing molecule to another) thus reducing ‘free radicals’ and is therefore believed to have cancer preventative qualities.


8. Selenoprotein V

Operates in the testes and is believed to be a part of sperm crea9. Selenoprotein S

Is believed to play a role in inflammatory and immune responses and operates in the inner cell.


10. Selenoprotein W:

Found in our muscles it is believed to work on muscle metabolism but there is no confirmed information on this.




Not getting enough selenium in out diet does not mean that there will be obvious symptoms but people who are deficient in selenium are more susceptible to some physiological problems.


Although it is relatively rare in humans selenium deficiency can occur if someones intestines are severely compromised or if the intravenous solution a patient is getting doesn’t have selenium in it.  People over 90 years of age also have trouble getting selenium into their systems.  In these people muscular weakness, muscle wasting and heart muscle problems begin to develop over time.  


Selenium deficiency has been correlated with higher overall cancer rates but not in cancer mortality rates.  Some believe that selenium has antioxidant effects but a study of over 60,000 participants showed no significant correlation between cancer and selenium antioxidant activity.


There is evidence that selenium helps in enhancing the effects of chemotherapy drugs.  Certain chemo drugs are more toxic when selenium is present.


In march 2009 supplements containing both vitamin E and selenium were reported to act as tumor suppressors and to affect gene expression.


The progression of HIV aids is strongly correlated with low levels of selenium.  It is believed this is because selenium either acts as an antioxidant directly or it is involved in gene encoding that slows the progression of the disease. 


Low levels of selenium have also been associated with recurrences in tuberculosis.


Keshan disease is a heart disease known in the selenium deficient regions of China.  The disease is closely related to low selenium intake.  Kashin-Beck disease causes a breakdown in joint cartilage and is associated with low levels of dietary selenium. This disease is also prevalent in the northern regions of China.




If you get over 400 mcg a day of selenium it becomes toxic to your body.  A condition called selenosis develops You’ll get a garlicky smell on your breath and gastrointestinal problems. Your hair will begin to fall out.  Your finger nails will begin to fall off.  You will become very tired and irritable and you will incur nervous system damage.  If you really over do it then you can end up with cirrhosis of the liver, pulmonary edema where air fills up around the cells in you lungs and starts to suffocate you and finally selenosis may finally kill you.