|Mineral Nutrient :: Selenium|
|Content Below:||What is Selenium · Benefits · Deficiency Signs · Foods · Supplements · RDA · Toxicity|
What is Selenium ?
Selenium is an essential trace mineral that is widely regarded in scientific communities as a potentially powerful antioxidant. Studies suggest that it may protect against cardiovascular disease and certain forms of cancer.
It is needed on a daily basis, and is found in tiny amounts in all organs of the body, with higher concentrations in the kidneys, spleen, pancreas, and liver, and in the testes and seminal vesicles in men.
The selenium content in food (plants, and indirectly animals, since these feed on the plants) depends on the level of the nutrient in the soil. While this is generally true for all minerals, it is particularly so for selenium.
For this reason, people who live in and consume mainly food from selenium depleted areas may require supplementation.
Selenium can be lost when food is processed or refined. For instance, the milling of grains into the refined flour that is used in almost all breads and baked products sold, removes most of its selenium, that is located in the bran and germ. Take more whole grains if possible, as refining removes a number of other nutrients as well.
It is one of the most important nutrients, as selenium benefits and impact to the body are wide-ranging. The main reason for this is that it is one of the most potent immune system boosters and antioxidants around.
It helps prevent oxidative damage to the body from free radicals, together with the other antioxidants such as glutathione, vitamin C, and vitamin E.
As an antioxidant, it helps to slow the aging process, and protects against a number of degenerative disorders. In one ten-year study, men who took 200 mg of selenium daily had 50% less risk of developing cancer compared to the norm.
In cases where oxidative stress appears to be the cause of rheumatoid arthritis or blood vessel damage leading to heart disease, low blood levels of selenium have been found to be a contributing factor.
The main ways that selenium benefits the body are summarized here.
|::||Selenium Benefits & Functions|
|1.||important antioxidant especially in combination with vitamin E|
|2.||in studies and large-scale clinical trials, selenium and vitamin E taken in combination have been shown to significantly reduce the risk of certain cancers, especially lung, gastrointestinal, prostate and colorectal cancer|
|3.||induces repair of DNA in damaged cells, and so limits growth of cancer cells|
|4.||critical component of one of the most powerful antioxidant enzymes in the body, glutathione peroxidase, that detoxifies harmful molecules, making it especially important for cancer protection|
|5.||as an antioxidant, selenium protects the body and immune system from oxidative damage by inhibiting harmful free radicals that damage cells|
|6.||one of the antioxidants that help slow oxidation of LDL and so lowers the risk of coronary artery disease|
|7.||preliminary studies indicate that selenium supplementation with other antioxidants can help protect against sunburn|
|8.||may protect the body against toxic effects of heavy metals like copper, mercury and arsenic, by binding to them to render them less harmful|
|9.||activates prostaglandins that regulate blood pressure|
|10.||some evidence that selenium helps reduce post-operative edema (swelling) and inflammation resulting from surgery or burns|
|11.||has been shown to reduce edema in pregnancy-related hypertension|
|12.||preliminary studies shows reduction in symptoms from elevated brain pressure, such as headaches, vomiting, nausea, and seizures|
|13.||has been shown in some studies to improve asthma symptoms|
|14.||critical for proper functioning of the thyroid gland and the production and regulation of thyroid hormones; may alleviate goitre|
|15.||may boost fertility as it enhances sperm production and movement|
|16.||essential for tissue elasticity|
|17.||has been used to treat skin disorders like eczema, acne and rosacea, and accelerate healing of burns, with some positive results|
|18.||strengthens the immune system|
|19.||evidence from preliminary research that selenium may prevent infections such as sepsis and erysipelas (a type of skin infection), and promote recovery from bronchitis and some types of pneumonia, due to its role in immune system function|
|20.||supplementation is sometimes prescribed by doctors for patients with HIV/AIDS, as the disease may cause malabsorption and depletion of nutrients, including selenium which appears to slow progression of the virus by boosting the immune system|
Selenium Deficiency Symptoms and Causes
Deficiency is generally rare. Where it occurs low dietary intake is the most common cause.
Since selenium content of food depends so much on the content in the soil it is grown, areas with selenium-poor soil are at higher risk of deficiency.
This is particularly so where the main source of food is local. Parts of the world with selenium-deficient soils include Finland, New Zealand, and some areas of China, Africa, and the US (Great Lakes region towards the New England states, and parts of the Atlantic Coast and Pacific Northwest).
Such areas have a high occurrence of selenium deficiency symptoms, such as Keshan disease in parts of China afflicting selenium-deficient children. It is treated by supplementation.
Other causes of low blood levels of selenium include :
- gastrointestinal disorders or malabsorption syndromes (including food allergies) that decrease the body’s ability to absorb nutrients
- high-dose steroid therapy also affects absorption of selenium
- cigarette-smoking or high intake of alcohol
- where the only source of nutrition is intravenously through the vein (IV therapy) over a long period of time
Mildly low levels of selenium does not usually result in any disorders. But if it is severe or prolonged, a number of selenium deficiency symptoms may appear, mostly as a consequence of oxidative stress.
|::||Selenium Deficiency Symptoms|
|1.||researchers believe that low selenium levels weaken the immune system and make the body more susceptible to stress and illnesses
|2.||studies show a correlation between low selenium levels and incidence of cancer, especially gynaecological, gastrointestinal, esophageal, lung, and prostate cancer
|3.||rheumatoid arthritis patients tend to have low blood levels of selenium
|4.||elevated blood pressure
|5.||risk of atherosclerosis leading to heart or coronary artery disease
|6.||research indicates that selenium deficiency worsens the effect of iodine deficiency on thyroid function, leading to hypothyroidism symptomized by lethargy, fatigue, depression, constipation, weight gain, intolerance to cold, heavy menstruation, dry skin, and hair loss, and that selenium supplements may help protect against goiter
|8.||hair or skin discoloration
|9.||whitened fingernail beds
|10.||Keshan disease (heart disorder symptomized by inflamed heart muscles or abnormal heartbeat)
|11.||Kashin-Beck disease (a disabling disease of the joints, characterized by stunted growth, deterioration of bone or joint tissue, or joint deformity)
|12.||severe deficiency coupled with malnutrition can cause breakdown of muscles characterized by pain or weakness in the muscles
The foods with selenium listed below are generally good sources. However the amount of selenium in a particular piece of food is heavily dependent on, and will vary with soil conditions.
Soil conditions will affect plant foods directly, and animal foods indirectly, as most animals rely on the plants for their diet.
Rich selenium food sources are
· Brazil nuts (one of the most concentrated selenium food sources) · mushrooms (button, shiitake, reishi) · fish (cod, flounder, halibut, herring, mackerel, salmon, smelts, red snapper, swordfish, tuna) · seafood (lobster, oyster, scallops, shellfish, shrimp).
Other foods with selenium include · blackstrap molasses · brewer’s yeast · butter · cheddar, cottage, and mozzarella cheese · egg · chives, garlic, onions, horseradish · herbs (alfalfa, burdock root, catnip, fennel seed, ginseng, raspberry leaf) · meat (beef, chicken, lamb, turkey) · raisins · sunflower and mustard seeds · vegetables (asparagus, broccoli, radish, spinach) · walnuts · wheat germ · whole grains and wholegrain products (oats, barley, brown rice, rye).
Taking vitamins and minerals in their correct balance is vital to the proper functioning of all vitamins. They work synergistically, which means that the effectiveness of any one nutrient requires, or is enhanced, sometimes dramatically, by the presence of certain other nutrients.
For this reason, if you are looking to take supplements for maintenance of optimal health, the recommended approach is to take a multi-vitamin that has the proper balance of all the necessary nutrients your body needs.
For a list of reputable top ranked vitamin and mineral supplements chosen in an independent supplement review, see Best Multivitamin Supplements. Many of these are manufactured to pharmaceutical or nutraceutical GMP compliance, which is the highest multivitamin standard possible.
Keep in mind, however, that while mineral supplements are useful to plug nutritional gaps that are almost inevitable in modern diets, and to ensure we get optimal doses of nutrients, they are no substitute for a good diet. Instead, use them to complement a healthy diet and lifestyle.
Selenium RDA (Recommended Dietary Allowance)
The Food & Nutrition Board of the Institute of Medicine, National Academy of Sciences, in their 1997-2001 collaboration between the US and Canada, set the daily Adequate Intake (AI) of Selenium as follows.
|Life Stage | Gender||Selenium Dosage | Day|
|Infants 0-6 mths||15* µg|
|Infants 7-12 mths||20* µg|
|Children 1-3 yrs||20 µg|
|Children 4-8 yrs||30 µg|
|Girls 9-13 Yrs||40 µg|
|Boys 9-13 Yrs||40 µg|
|Females 14-18 Yrs||55 µg|
|Males 14-18 Yrs||55 µg|
|Females 19-50 Yrs||55 µg|
|Males 19-50 Yrs||55 µg|
|Females older than 50 Yrs||55 µg|
|Males older than 50 Yrs||55 µg|
|Pregnant Women 14-18 Yrs||60 µg|
|Pregnant Women 19-50 Yrs||60 µg|
|Lactating Mothers 14-18 Yrs||70 µg|
|Lactating Mothers 19-50 Yrs||70 µg|
These dosages are the minimum required per day to ward off deficiency. In therapeutic use of this nutrient, dosage is increased as necessary for the ailment, keeping in mind Selenium toxicity levels.
1 µg = 1 mcg = 1 microgram = 1/1,000,000 of a gram
1 mg = 1 milligram = 1/1,000 of a gram
* Indicates AI figures based on Dietary Reference Intake (DRI) figures
Selenium Overdose Symptoms, Toxicity Level & Side Effects
Toxicity is rare, and is more likely to arise from supplement overdose than from foods with selenium.
Excess selenium can cause a condition known as selenosis, that leads to irritability, fatigue, gastrointestinal upset (nausea, vomiting, stomach pain, diarrhoea, garlic breath, metallic taste in the mouth), hair and nail loss or blotchy nail beds, and mild nerve damage.
Other symptoms are dermatitis or skin rash or skin lesions, impaired liver or kidneys, jaundice, thyroid dysfunction, and growth retardation.
Extreme overdose can cause fever, breathing difficulties, changes to the heart, and if the levels are high enough, even death.
Those who are at high risk or with a history of non-melanoma skin cancer should avoid taking selenium supplements, as studies suggest that it might actually aggravate risk of the cancer.
The Food and Nutrition Board of the Institute of Medicine has set Tolerable Upper Intake Levels (UL) for selenium. These are the levels above which there is risk of selenium side effects, especially if taken over a long time.
Tolerable Upper Intake Levels (UL) for Selenium per Day
|0 to 6 months||45 µg||45 µg|
|7 to 12 months||60 µg||60 µg|
|1 to 3 years||90 µg||90 µg|
|4 to 8 years||150 µg||150 µg|
|9 to 13 years||280 µg||280 µg|
|14 years & above||400 µg||400 µg||400 µg||400 µg|
The ULs do not apply to therapeutic use of selenium for treatment, which should be under the supervision of a healthcare professional.
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|1.||Institute of Medicine, Food and Nutrition Board. Dietary reference intakes for vitamin C, vitamin E, selenium, and carotenoids. Washington, DC: National Academy Press; 2000.|
|2.||U.S. National Libary of Medicine [NLM] & National Institutes of Health [NIH]: MedlinePlus. NLM-NIH home page. <http://www.nlm.nih.gov/medlineplus>. Use the built-in search function to find specific data. Accessed 2009 March – June.|
|3.||National Institutes of Health, NIH Clinical Center: Office of Dietary Supplements [ODS]. ODS home page. <http://ods.od.nih.gov>. Use the built-in search function to find specific data. Accessed 2009 Mar – Jun.|
|4.||The George Mateljan Foundation: The world’s healthiest foods [WHFoods]. WHFoods home page. <http://www.whfoods.com>. Accessed 2009 March – June.|
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|7.||Ulene A. Dr. Art Ulene’s complete guide to vitamins, minerals and herbs. New York, NY: Avery Publishing; 2000.|