Selenium is an essential component of glutathione peroxidase, an antioxidant enzyme formed from selenium and the tri-peptide glutathione. Along with superoxide dismutase (SOD), glutathione is one of the most potent substances made by the body for the purpose of cell protection. While SOD scavenges superoxide radicals, glutathione peroxidase quenches hydroxyl radicals and hydrogen peroxide. (Hydroxyl radicals are among the most destructive of free radicals, and are implicated in damage to cellular proteins, cell membranes, DNA and lipids.) As with SOD, scientists have demonstrated a strong statistical association in mammalian species between tissue glutathione peroxidase levels and life expectancy. Selenium may also possess its own antioxidant activity independent of its role in glutathione peroxidase. Of special interest is the relationship between selenium and vitamin E, the primary lipid-protective vitamin. As an antioxidant, selenium works synergistically with vitamin E in the protection of fats and cell membranes. Selenium and vitamin E can, to an extent, substitute for one another in some of their antioxidant actions (however, it is important to note that neither nutrient can replace the other in terms of their overall function – both must be ingested in adequate amounts in order to sustain human life). The antioxidant activity of selenium (especially in combination with vitamin E) may provide protection against many of the ravages of ageing; diseases associated with cell mutation; degeneration of the cardiovascular system, eyes and joints; various inflammatory conditions; immunological dysfunction; male fertility problems (due to oxidative sperm damage); and many other challenges to health.


The glutathione component of glutathione peroxidase is the body’s most important detoxification compound. Though glutathione functions in all tissue cells, the liver contains a particularly high concentration, due to its primary responsibility of removing toxins. Selenium enhances glutathione activity, as well as facilitating glutathione peroxidase synthesis. As mentioned, glutathione peroxidase protects the cells from highly damaging free radicals. Glutathione helps eliminate and/or reduces the destructiveness of a wide range of potentially toxic compounds such as environmental chemicals and pesticides, hormones, metabolic end-products, medications, heavy metals and so on. Regarding heavy metals, selenium impairs the uptake and increases excretion of cadmium (i.e. from tobacco smoke and air pollution). Selenium also binds both organic and inorganic forms of mercury, and studies suggest that it can protect against the entire range of mercury’s toxic effects. In addition, lead and aluminium are antagonised by this mineral. Of special importance to the public health is the ability of selenium to neutralise and detoxify free radicals formed by fat oxidation/metabolism (i.e. lipid peroxides). Lipid peroxides catalyse fast-spreading free radical chain reactions that damage lipids, cellular membranes, proteins and DNA and increase the risk of liver damage, cardiovascular disease and diseases associated with cell damage and mutation.


Selenium is one of the most important of all nutrients in the protection of cells within the body. Although its antioxidant properties account for a great deal of selenium’s cell-protective activity, additionally there are many other biochemical facets of selenium which contribute in this respect. For example, selenium detoxifies many varieties of cell-damaging compounds such as heavy metals and numerous environmental carcinogens/mutagens. The influence of selenium on detoxification is further boosted by its protective effect on liver function. Selenium also stimulates immunological response. Numerous large-scale epidemiological studies confirm a clear-cut link between higher intakes of selenium and a lower risk of diseases associated with cell mutation (and vice versa). Although selenium supplementation has been shown to possess preventive effects in this respect, research suggests that its protective properties may be significantly boosted by other antioxidant nutrients such as vitamin E.


Many antioxidant nutrients have demonstrated protective benefits on the cardiovascular system, and selenium is no exception. There is a strong statistical association in epidemiological research between low selenium intakes and high rates of cardiovascular disease (and vice versa). Among other benefits, selenium has been shown to address three cardiovascular risk factors – vascular cholesterol deposits, the ratio of HDL (good) and LDL (bad) cholesterol and the stickiness of blood platelets. Studies highlight that selenium reduces cholesterol deposits, increases the proportion of HDL compared to LDL cholesterol and reduces platelet aggregation (thereby protecting against excessive blood clotting). It is likely that the augmentation of vitamin E (see antioxidant activity above) and the influence on glutathione peroxidase account for much of the benefit of selenium in heart health. Vitamin E (with added assistance from selenium) prevents oxidation of fat and cholesterol in the arteries. LDL cholesterol oxidation is a major risk factor in atherosclerosis development.


The eyes are among the most susceptible body tissues to free radical damage. They are constantly under attack from not only the internally produced oxidative radicals that affect all cells, but also those generated through exposure to ultraviolet rays, ozone, air pollution and so on. Such damage can either cause or exacerbate degenerative eyes disorders such as cataracts and macular degeneration as well as the general reduction in vision associated with the ageing process. Presumably due to this high susceptibility, healthy eye tissue carries a disproportionately high concentration of antioxidants (such as the enzymes glutathione peroxidase, superoxide dismutase (SOD) and catalase, and individual antioxidant nutrients including carotenoids (e.g. lutein), selenium, vitamin C and vitamin E). Selenium concentration in the aqueous humour of the eyes is particularly critical to the subject of cataracts; a 1995 study showed that the selenium concentration in the aqueous humour of cataract patients is only around 60% of levels found in healthy subjects. This may help explain the rather astonishing scientific discovery that the hydrogen peroxide level in the cataract-affected aqueous humour is 25 times higher than normal. The free radical hydrogen peroxide accelerates oxidation of lipids in eye tissue and adversely affects the eye’s cellular fluid balance. The selenium-dependent enzyme glutathione peroxidase effectively scavenges hydrogen peroxide.


The importance of selenium in pregnancy and lactation is dramatically demonstrated in research linking selenium deficiency to Sudden Infant Death Syndrome and certain disorders for which heart damage (in the form of focal cardiac necrosis) is a common manifestation. It has been theorised that the focal cardiac necrosis seen in newborns afflicted with these disorders is probably caused by accelerated oxidation due to lack of selenium and the associated adverse affect on vitamin E function. Although Sudden Infant Death Syndrome is currently not officially linked to any particular cause, it may be significant that after reviewing 200 cases, a study published in the journal Forensic Science International reported that all 200 babies had been affected by focal cardiac necrosis. It is worth mentioning that a serious childhood heart disorder called Keshan’s Disease tends to only occur in areas of China with selenium-deficient soil. In response to this disease Chinese physicians carried out a study in 1974 where thousands of at-risk children received either selenium supplementation or placebo. During 1974 and 1975 the number of Keshan’s cases in the placebo group was more than 6 times higher than in the selenium group. The benefits of the selenium were so dramatic that in 1976 the use of the placebo was eliminated and all of the 12,579 children were given selenium.


Although a lack of any essential nutrient will impair immune function, a selenium deficiency is especially detrimental. Research demonstrates that low selenium status is associated with weakened function of the thymus (the master gland of immunity) and suppressed white blood cell activity. It has also been established that selenium supplementation promotes immune function, as highlighted in a 1994 study showing that 200ug of selenium per day increased natural killer cell activity by more than 80% and the ability of lymphocytes to kill abnormal cells by almost 120%. What is especially interesting about this research is the fact that the individuals receiving selenium had normal selenium status to begin with, showing that selenium supplementation does not only elevate immunity in those who are selenium deficient.

Potential applications

•        Protection against free radicals

•        Slowing the ageing process

•        Cell protection

•        Protection against diseases associated with cell mutation

•        Liver protection

•        Cataracts

•        Detoxification

•        Elimination of and/or protection against heavy metals (i.e. cadmium, mercury, lead)

•        Arthritis and various other inflammatory conditions

•        Cardiovascular health (general)

•        Promoting healthy foetal growth and development

•        Immune dysfunction

•        Thyroid dysfunction

•        Male fertility problems

Typical Supplemental Dosage Range

•        50-400ug per day


•        None established

Common Supplement Forms/Sources

•        Sodium selenite/selenate (inorganic)

•        Selenomethionine (organic)

•        Yeast-bound selenium (organic)

Common Food Sources

•        Brazil nuts

•        Butter

•        Liver

•        Shellfish

•        Fish

•        Apple cider vinegar

•        Whole wheat*

•        Oats*

•        Brown rice*

•        Milk

•        Red swiss chard

The selenium content of cereal grains is highly variable depending on the content of selenium in the soil. Therefore, grains grown in selenium- deficient soil will be low in selenium.

Please note: Research suggests that inorganic selenium (selenite/selenate) has a much higher toxicity than the organic forms (selenomethionine, yeast-bound selenium). The inorganic forms are also likely to be less effective and may even be ineffective in correcting selenium deficiency. In addition, as opposed to the organic forms, inorganic selenium may actually encourage free radical formation, thus calling into question the safety of sodium selenite and sodium selenate in human nutrition.

Contraindications/Cautions/lnteractions/Toxicity Concerns

•        Inorganic forms of selenium (e.g. sodium selenite/selenate) may become toxic at a daily intake level of around 850-1000ug; it has been reported that toxicity from organic selenium may begin at levels 2000-3000ug per day.

•        Symptoms/signs of selenium toxicity include nausea and vomiting, metallic taste in the mouth, dizziness, hair loss, irritability, nervous tension, fatigue, neuropathy, nail defects, skin lesions, garlic odour on the breath and perspiration, rapid breathing, spinal cord inflammation and bone marrow dysfunction. In extreme cases, selenium toxicity can be fatal.

•        Yeast-derived selenium supplements should not be used by patients taking monoamine oxidase (MAO) inhibitors unless on the advice and under the strict monitoring of a physician. Yeast-free selenium supplements can be used as an alternative.

Please note: Studies suggest that inorganic selenium (selenite/selenate) has a much higher toxicity than the organic forms (selenomethionine, yeast-bound selenium). The inorganic forms are also likely to be less effective and may even be ineffective in correcting selenium deficiency. In addition, as opposed to the organic forms, inorganic selenium may actually encourage free radical formation, thus calling into question the safety of sodium selenite and sodium selenate in human nutrition.

Agents/Factors Which Deplete Levels, Impair Absorption and/or Inhibit Activity

•        Vitamin C (very high doses)

•        Zinc (very high doses)

•        Heavy metals (i.e. lead, mercury, cadmium)

•        Chemotherapeutic drugs

Possible Signs/Symptoms Associated with Deficiency

•        Cardiomyopathy

•        Focal cardiac necrosis

•        Keshan’s Disease

•        Diseases associated with cell mutation

•        Liver necrosis

•        Cataracts

•        Blindness

•        Toxic overload

•        Infertility

•        Arthritis and various other inflammatory conditions

•        Premature ageing

•        Heavy metal toxicity

•        Psoriasis

•        Eczema

•        Impaired mental development

•        Sudden Infant Death Syndrome (SIDS)

•        Immune dysfunction

•        Thyroid dysfunction

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