Although considered an important trace mineral since the 1950s, selenium's many functions are still being defined by researchers. Indeed, the benefits of selenium are many, and, without adequate intake, the body might be subject to a range illnesses and stresses. Many are unclear both in terms of how much of this mineral they need to show a positive selenium status, and the types of foods and supplements in which to derive sufficient levels of selenium.
One thing is for sure: selenium, given its trace mineral status, should be taken in small amounts, otherwise toxic build-up may occur. In fact, in areas where soil concentrations of selenium are excessively high, plants that are grown therein are toxic to humans and animals alike (indeed, many of selenium's compounds have modes of action similar to arsenic).
Conversely, many areas of soil are deficient in selenium, and, as a result, those eating foods produced in this land are advised to seek out supplements, and foods, with added selenium.
Selenium is nothing new, having been discovered in 1817, in Sweden, by scientist Jons Jacob. However, its disease preventing actions were demonstrated 32 years later, in 1950, when researchers in the US and Germany collaborated to highlight its important antioxidant actions.
In 1973, selenium was shown, by researchers at the University of Wisconsin, to be a co-factor of glutathione peroxidase - a detoxifying substance. In light of its historical underpinnings, it is safe to say selenium is immensely important to health and well-being. But why is selenium so important, what are its benefits, and why is selenium deficiency problematic? Read on to find out.
What Is Selenium?
As mentioned, selenium is a trace mineral, or micro-nutrient, important for health and well-being, and a component of all known forms of life (in humans selenium concentrations are highest in the liver and kidneys). It exerts its beneficial effects by combining with proteins to make selenoproteins. These selenoproteins are essentially antioxidant enzymes (glutathione peroxidase specifically), with antioxidant properties, which help to prevent cellular damage resulting from free radical build-up.
Denoted on the periodic table with the symbol Se, and atomic number 34, selenium is chemically related to sulphur and tellurium, and regarded as a toxic non-metal. Copper, sliver and lead are the main sulphide ores, in which selenium, as selenide, occurs.
Selenium On The Periodic Table Of Elements.
Click To Enlarge.
Selenium, independently, or in tandem with vitamin-E, help to ward off several types of disorder including cancer, 2,10 cataracts, 8,11 heart disease, 2,7,10 fertility problems 8, and neurological conditions/psychological problems 6,9 as mounting research has shown.
These problems might be countered by (in its selenoprotein form) selenium's ability to minimise free radical proliferation. It also plays a major role in the functioning of the thyroid gland, which has mental health ramafications.
Click To Enlarge.
What Are Selenium's Benefits?
- Protection Against Certain Types Of Cancer.
People with higher blood concentrations of selenium are thought to have a lessened chance of acquiring prostate, lung, co-rectal or skin cancers.2 In population studies, people in selenium deficient areas have been shown to have higher rates of these cancers compared to the general population, thus strengthening the link between optimum selenium status and free-radical counteraction. Some researchers, on the other hand, believe selenium may work by improving the body's natural immune response against cancer cells and suppressing development of blood vessels to the tumour.
Good news for men: a recent study found that men who had the highest blood concentrations of selenium, cut their chances of getting prostate cancer by one-half to two-thirds, compared to men with lower levels. In one of the most famous selenium studies, researchers found, upon analysing toe clippings (an accurate analytical tool for assessing nutrient status), men who had higher levels of selenium, developed 65% fewer cases of advanced prostate cancer.10
Earlier cancer studies found cancer patients with low levels of selenium, developed more subsequent tumours. Survival rates for cancer patients with low selenium levels were generally shown to be shorter.
Enhancing Of Immune function.5,6
Selenium's immune boosting properties are thought to stem from its ability to strengthen phagocytes (white blood cells that attack invading toxins). It has been shown, also, that selenium enhances the capacity of lymphocytes, to proliferate, and differentiate into cytotoxic effector cells, which kill antibody-coated target cells.3 This same study demonstrated that the molecular mechanism mediating selenium's effect on immunity is not linked to the function of selenium as an antioxidant, thus highlighting its separate immune bolstering role.
Protection Against Heart Disease.
Serious heart defects in large animals (cattle etc) have been attributed to selenium deficiency. An abnormally low concentration of coenzyme Q10 (a substance essential for healthy heart functioning) in animals with heart defects, is thought to be linked to a deficiency in selenium and vitamin-E (a vitamin that teams with selenium to boost the immune system, and fight
disease)9 - both selenium and vitamin-E are needed to maintain adequate coenzyme Q10.
Additional lines of evidence suggest oxidative stress created by free-radicals, as a result of selenium deficiency, promote heart disease.7,10 Oxidised LDL cholesterol plays major role in heart disease due to its propensity to contribute to plaque formation, and selenium is thought to limit this oxidation. Selenium may even increase the proportion of beneficial HDL cholesterol to the problematic LDL.
Protection Against Arthritis.
Sufferers of arthritis have been found to have reduced selenium levels in their blood. Arthritis, a chronic disease that causes pain, stiffness, swelling, and loss of function in joints, often results from excessive free-radicals made by the immune system in response to invading organisms.10 Thus, controlling free-radicals with the help of selenium might relieve the symptoms of arthritis.
Prevention Of Cataracts.
Studies have found that eye lenses that are affected by cataracts have about one-sixth of the normal amount of selenium.10,11 As a result, researchers believe a selenium deficiency might be a contributory factor in cataract formation.
Once again, it is selenium's antioxidant function, which fights the free-radical build-up, that negates damage to the eye's lens (the site of cataracts) and the macula at the centre of the eye's retina.10 In the latter case, selenium is also shown to prevent macula degeneration.
Detoxification Of Poisons.
Toxic metals such as arsenic, mercury, and cadmium undergo a reduction in toxicity when they bind with selenium.8 Shampoos, and various topical medications, have added to them, selenium to offset their toxic effect.
Protection Of Genetic Materials.
Selenium helps to prevent cellular DNA damage resulting from free-radical build-up.
Enhance Psychological Well-Being.
Low levels of selenium have been linked to cognitive decline in the elderly,
as well as, confusion, depression, fatigue and anxiety in the adult general
A 2004 finding indicated selenium might positively effect mood,
behaviour and cognitive function due to the significant role it plays in
thyroid regulation.1,6 It was suggested that patients who have a combination
of hypothyroidism, depression and increased susceptibility to viral
infections, could be deficient in selenium.
Many vital nutrients are depleted from the body as a result of the damage
incurred by AIDS, and selenium is the one micro-nutrient most commonly
associated with AIDS, so much so, it has been linked closely to a high risk
of death from this disease.
Retroviruses. like HIV/AIDS, cause the
depression of selenium by encoding the gene for the human selonoprotein
glutathione peroxidase.10 As mentioned, glutathione peroxidase is the
antioxidant enzyme form of selenium, and if its gene is encoded, in response
to retroviral attack, the virus will replicate indefinitely by continually
depriving the body of glutathione.
Opportunistic pathogens will then invade
the immune system to further deplete the body of selenium, which compromises
the immune system further, and hastens AIDS related death.
Prevention Of Fertility Problems.
Selenium deficiency has been linked to sperm abnormalities and increased
risk of early pregnancy loss.11, 12 In fact, healthy sperm formation is
dependant, to a large extent, on selenium intake - blood levels of selenium
are found to be lower in men with low sperm counts.12 sufficient blood
levels of selenium also have been shown to help prevent chromosome breakage,
which is known to be a leading cause of birth defects and miscarriages.
Signs Of Deficiency
Selenium Deficiency Might Include:
- Muscle weakness and fatigue.
- A risk for cancer.
- Immune system problems.
- Heart disease.
- Inflammatory problems (especially skin related).
Dangers Of Over-Consumption
Over-supplementation of selenium can result in a serious toxic reaction,
although this is rare, given a considerable amount would be needed to have
this effect. An overdose could cause hair loss, nausea, vomiting, and
fingernail changes (which occurred in one case where people consumed
500-times the RDA).11,13,14,15
This condition is called selenosis, and can
include additional symptoms of mild nerve damage and gastrointestinal
distress.13 A lesser, more likely toxic effect, might cause depression,
garlicky breath and anxiety. However, given many rely on diet for their
selenium requirement, any level of toxicity is unlikely, for these people.
Experts caution against more than 200mcg used on a long-term basis, until a
safe dosage is ascertained.
Note: mcg = microgram" or one-millionth of a gram.
Recommended Intake (dosage):
The Recommended Daily Allowances (RDA) For Selenium Are Set At The Following: 4,8
- Infants under six-months: 10mcg.
- Children, one-six years: 20mcg.
- Children seven-ten: 30mcg.
- Males 11-14: 40mcg.
- Males 15-18: 50mcg.
- Males 19 and over: 70mcg.
- Females 11-14: 45mcg.
- Females 15-18: 50mcg.
- Females 19 and over: 55mcg.
- During pregnancy: 65mcg.
- Breast feeding: 75mcg.
However, dosage information varies drastically for special populations.
These Are As Follows: 11
- For preventing against the effects of again or for cancer prevention:
- Macular degeneration and cataract prevention: 200-400mcg-per-day.
The Best Sources Of Selenium
The most concentrated food source of selenium is the Brazil nut, with a
single nut containing almost 120mcg (twice the RDA). Thus, it is advisable
to eat Brazil nuts only very occasionally, due to the potentially toxic
effect they may have, in light of their high selenium levels (one ounce may
contain up to 600mcgs).
The most common sources of selenium include bread and meat. Animals that eat
grains or plants grown in selenium rich soil are likely to have higher
levels of selenium in their meat content. Seafood, as well, is often rich in
selenium. Three-ounces of tuna, for example, has a relatively high 63mcgs of
Supplemental selenium can be used in instances where it has been shown that
one is clearly deficient in this mineral. Those with widespread infection,
or gastrointestinal problems such as Crohn's disease16, are most likely to
be deficient in selenium, and would therefore qualify for larger,
supplemental dosages. Selenium supplements can also be used, on a smaller
scale, by the general population, to ensure they are not lacking in this
Selenium, as a vital trace-mineral, is important in terms of ensuring
complete health and well-being. Selenium deficiency has been linked to all
major health conditions, from cancer to heart-disease, low immunity to
cataracts. Ensure all nutritional basis are covered by eating selenium rich
foods, and supplementing if necessary.
- Arthur JR. The role of selenium in thyroid hormone metabolism. Can J
Physiol Pharmacol 1991;69:1648-52.
- Hercberg S, Galan P, Preziosi P, Roussel AM, Arnaud J, Richard MJ,
Malvy D, Paul-Dauphin A, Briancon S, Favier A. Background and rationale
behind the SU.VI.MAX Study, a prevention trial using nutritional doses of a
combination of antioxidant vitamins and minerals to reduce cardiovascular
diseases and cancers. Supplementation en VItamines et Mineraux AntiXydants
Study. Int J Vitam Nutr Res 1998;68:3-20
- Kiremidjian-Schumacher L,. & Roy M.(1998). Selenium and Immune
Function. Suppl 1:50-6
- Levander OA. Scientific rationale for the 1989 recommended dietary
allowance for selenium. J Am Diet Assoc 1991;91:1572-6.
- McKenzie RC, Rafferty TS, Beckett GJ. Selenium: an essential element
for immune function. Immunol Today 1998;19:342-5.
- M. Ferencik, L. Ebringer. Modulatory effects of selenium and zinc on
the immune system. Folia Microbiol. 2003 48(3), 417-426.
- Neve, J. (1996) Selenium as a risk factor for cardiovascular diseases.
J. Cardiovasc. Risk 3:42-47.
- Roberts, A., O'Brien, M., & Subak-Sharpe, G.(2001) Nutraceuticals: the
Complete Encyclopaedia. Pedigree; NY.
- Rayman MP. "The importance of selenium to human health." Lancet.
- Turner, S.(1992). New Research: Selenium May Protect Against Viruses,
Heart Disease, Arthritis, Hepatitis, and Cancer. HMS Monitor.
- Whole-Mind MD.com.(2000). Selenium. [Online]
- Glenville, M.(2005). Natural Solutions to Infertility. The Natural
Health Website for Women. [Online]
- Koller LD and Exon JH. The two faces of selenium-deficiency and
toxicity are similar in animals and man. Can J Vet Res 1986;50:297-306.
- Hathcock J. Vitamins and minerals: Efficacy and safety. Am J Clin Nutr
- Raisbeck MF, Dahl ER, Sanchez DA, Belden EL, O'Toole D. Naturally
occurring selenosis in Wyoming. J Vet Diagn Invest 1993;5:84-7.
- Kuroki F, Matsumoto T, Lida M. Selenium is depleted in Crohn's disease
on enteral nutrition. Digestive Diseases 2003;21:266-70.
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