Selenium (Se) is an essential trace mineral used for many important body functions. Being essential means we need to obtain it from our diet and even though it is a only needed in trace amounts it is vital for health for such things as thyroid function, sperm motility, healthy metabolism and as an antioxidant. In fact, it is considered one the body’s main antioxidant nutrients, working as part of the enzyme – Glutathione peroxidase. This important enzyme prevents free-radical formation.
Free-radicals and reactive oxygen species (ROS) are generated by our body by various internal systems, from exposure to different physiochemical conditions or disease. A balance between free radicals and antioxidants is necessary for proper physiological function. If free radicals overwhelm the body's ability to regulate them, a condition known as oxidative stress is the result.
Trace minerals are only needed in very small quantities in the body, but they perform essential roles. Too much or too little can have a catastrophic effect on our body, even be fatal.
The Role of Selenium in the Body
Thyroid Function. Selenium is involved with an enzyme that converts the thyroid hormone to its active form (by facilitating the conversion of T4 thyroid hormone into the active form T3). It is very important in the prevention of oxidative stress on the thyroid.
Out of all the tissue in the body, the thyroid contains the most selenium, showing how important this mineral is to thyroid health.
Low selenium has been implicated in diseases of the thyroid such as Hashimoto’s thyroiditis. The thyroid is important to our body as it regulates metabolism and controls growth and development.
As an antioxidant. Oxidative stress produces free radicals and cause many diseases in our body like cancer, heart disease and other degenerative conditions of ageing. Other factors such as such as pollution, radiation, cigarette smoke and herbicides can create an abundance of free radicals which can lead to premature ageing and damage to cells in the body. Even though oxidative stress is a normal part of metabolism, too much leads to disease. Providing the right nutrients to balance our antioxidant system is important to prevent degenerative diseases.
Radiation therapy. Studies have shown that supplementation of selenium may reduce the side effects of radiation therapy.
Cardiovascular disorders - vascular endothelial cells are damaged by oxidative stress which also exacerbates cardiovascular diseases such as atherosclerosis, hypertension, and congestive heart failure. Selenoproteins are crucially involved in the cellular antioxidant defence system, thus selenium may help to prevent or treat cardiovascular disease.
Immune function. Selenium supports our immune system in its role preventing the invasion of virus, bacteria and inflammation. It does this by reducing oxidative stress and strengthening and enhancing the immune system.
Asthma. Oxidative stress can play a major role in inflammation of the airways.
Asthma is a chronic condition that results in a narrowing of the airways of the lungs, excess production of mucous and difficulty breathing. One study showed an improvement in asthma with supplementation of selenium supporting the body’s ability to eliminate damaging free radicals
Neurological diseases. Oxidative stress has been implicated in a number of neurological diseases such as Parkinson’s, multiple sclerosis and Alzheimer’s disease.
Cardiovascular disorders - vascular endothelial cells are damaged by oxidative stress which also exacerbates cardiovascular diseases such as atherosclerosis, hypertension, and congestive heart failure.
Selenoproteins are crucially involved in the cellular antioxidant defence system, selenium can help to prevent or treat cardiovascular disease.
Muscle disorders - Selenium deficiency is associated with myotonic dystrophy (a genetic muscle disorder) causing weakness and muscle pain. Keshan disease, a potentially fatal cardiomyopathy.
Some Other functions facilitated by selenium include:
- Reduce harmful toxicities of chemotherapy and radiotherapy without compromising drug efficacy
- Anti-tumorigenic
- Anti-mutagenic
- Detoxification of chemicals
- Improves sperm motility and maturation
- Facilitates the recycling of vitamin C and E in the body
- Inhibits platelet aggregation (blood clotting)
- Inhibits oxidation of fats in the body
- Increases HDL:LDL ratio
- Stimulates DNA Repair
Selenium works well with vitamin B, C, E, Co enzyme Q10, cysteine, glutathione, methionine, zinc and iodine.
Sources of Selenium
We should be able to consume all our trace minerals from our diet, but in some cases, this may not be possible and supplementing may be neccessary.
Selenium can be found in soil, water and some foods, depending on where they are grown and the richness of the soil in selenium. In Australia the main food sources are seafood, meats, eggs, poultry and cereals. Selenium is available as a supplement and sodium selenite powder is fed to animals in areas where soil is selenium deficient. It is considered safe if taken in moderation but can be toxic to the body in high doses.
Excess selenium is excreted through the urine with a small amount through faeces.
How much do you need?
Recommendations for Selenium intake differs from different countries due to lifestyle and diseased state – e.g. diabetes, atherosclerosis. The World Health Organisation (WHO) has recommends a dose of selenium for adults to be 30 to 40 μg/day and suggests that daily intake up to 400 μg selenium is to be considered safe.
Assessment of selenium levels in the body can be done through hair or nail analysis or selenium dependant glutathione and selenoproteins in blood.
What about getting too much?
Excessive doses of selenium are characterised by continuous vomiting, garlic breath, mucosal irritation, stomach pain, excess salivation, the destruction of blood cells, death of the liver, cerebral and pulmonary oedema, coma and death – known as selenium intoxification.
Interactions
Some medicine may reduce the blood levels of selenium in the body. These include: some corticosteroids and some oral contraceptives.
Anabolic steroids, mercury diuretics and chemotherapeutic agents can decrease the levels of selenium in the body.
Summary
- Selenium is an essential trace mineral that forms part of the body’s antioxidant enzyme glutathione peroxidase.
- Selenium protects the body from free-radical damage.
- Selenium supports the health and function of the immune system.
- Selenium supports the formation, development and motility of sperm.
- Selenium is essential for maintaining healthy thyroid function.
- Selenium may help conditions associated with free-radical damage and inflammation.
References
- Whitney, Eleanor Noss; Cataldo, Corinne Balog; Rolfes, Sharon Rady; 2002, Understanding Normal and Clinical Nutrition 6th Edition, Wadsworth/Thompsons Learning, Australia
- Henry, Osiecki; The Nutrient Bible 9th Edition, Bio Concepts, AG Publishing; QLD, Australia
- https://www.nrv.gov.au/nutrients/selenium
- https://www.researchgate.net/publication/7525256_Selenium_in_Australia_Selenium_status_and_biofortification_of_wheat_for_better_health
- https://www.cancer.org.au/content/pdf/CancerControlPolicy/PositionStatements/PS_Selenium_%20August_2005_Reviewed_July_2009.pdf
- https://www.mja.com.au/journal/2006/185/7/accidental-death-acute-selenium-poisoning
- Selenium: its role as antioxidant in human health https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2698273/
- Regulation and function of selenoproteins in human disease https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2912286/
- Supplementation of Micronutrient Selenium in Metabolic Diseases: Its Role as an Antioxidant https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5758946/
- Selenium, Selenoproteins, and Immunity https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6163284/
- Induction of oxidative stress and cell apoptosis by selenium: the cure against oral carcinoma https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5768350/
- The Interaction of Selenium with Chemotherapy and Radiation on Normal and Malignant Human Mononuclear Blood Cells https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6214079/
- The Role of Selenium in Inflammation and Immunity: From Molecular Mechanisms to Therapeutic Opportunities https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3277928/
- Selenium and Thyroid Disease: From Pathophysiology to Treatment https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5307254/
- https://www.nhlbi.nih.gov/health-topics/asthma
- Decreased consumption of corticosteroids after selenium supplementation in corticoid-dependent asthmatics. https://www.ncbi.nlm.nih.gov/pubmed/12061082
- https://www.healthline.com/nutrition/selenium-benefits#section7
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