Selenium (Se) is a nonmetallic element. No commercially important ores of selenium exist. It is usually obtained as by-product in the refining of copper sulfide, with which it occurs as an impurity. Selenium occurs naturally in organic form in two unusual amino acids, selenomethionine and selenocysteine.
The role of selenium in human nutrition and other therapeutic applications provoked intense controversy from about 1980 into the late 2000s. In contrast to such major minerals as magnesium and calcium, neither selenium’s benefits nor its toxic aspects are fully understood. In the late twentieth century selenium was considered a toxic element that was not necessary to human health. In 1989, however, selenium was reclassified as an essential micronutrient in a balanced human diet when the National Research Council established the first recommended daily allowance (RDA) for it. It is considered a minor mineral, or a trace element, as distinct from a major mineral such as calcium or phosphorus or an electrolyte such as sodium or chloride. The human body contains less than 1 mg of selenium. The selenium is concentrated in the liver, kidneys, and pancreas. In males, selenium is also found in the testes and seminal vesicles. Selenium has a variety of applications in the late 2000s, ranging from standard external preparations for skin problems to experimental and theoretical applications in nutrition and internal medicine.
Naturopaths use selenium supplements to treat asthma, acne, tendinitis, infertility in men, and postmenopausal disorders in women. Selenium is also considered an important component in naturopathic life extension (longevity) diets because of its role in tissue repair and maintaining the youthful elasticity of skin.
Selenium has been used since the 1960s in dandruff shampoos and topical medications for such skin disorders as folliculitis (hot tub syndrome) and tinea versicolor, a mild infection of the skin caused by the yeast-like fungus Pityrosporum orbiculare. A compound of selenium, selenium sulfide, has antibiotic and antifungal properties. It is absorbed by the outermost layer of skin cells, the epithelium. Inside the cells, the compound splits into selenium and sulfide ions. The selenium ions counteract the enzymes that are responsible for producing new epithelial cells, thus lowering the turnover of surface skin cells. As a result, itching and flaking of the skin associated with dandruff and tinea versicolor is reduced.
If you have a selenium deficiency, we recommend taking:
Prior to 1989, there were no established recommended daily allowance (RDA) values for selenium. In 1989, the National Research Council of the National Academy of Sciences defined the RDAs for seleniumas
- Children, less than six months of age: 15g/day;
- seven to 12 months: 20g/day; males and females
- one to three years: 20g/day;
- four to eight years: 30g/day;
- nine to 13 years: 40g/day;
- males, over 14 years: 55g/day;
- females, over 14 years: 60g/day;
- pregnant and lactating women: 70g/day.
The amount of selenium in the diet is influenced by its level in the soil. Most selenium is absorbed fromfood products, whether plants grown in the soil or animals that have eaten the plants.Much of the selenium in foods is lost during processing. About 60%of dietary selenium is absorbed as food passes through the intestines. Selenium leaves the body in the urine and feces; males also lose some selenium through ejaculation of semen. Selenium levels in soil vary widely, not only in different countries but also across different regions.
Foods that are high in selenium contain the element in an organic form, selenomethionine or selenocysteine. This form of selenium is considerably less toxic than inorganic compounds of selenium or elemental selenium. Good sources of selenium include brewer’s yeast, wheat germ, wheat bran, kelp (seaweed), shellfish, Brazil nuts, barley, and oats. Onions, garlic, mushrooms, broccoli, and Swiss chard may contain high amounts of selenium if they are grown in selenium-rich soil. Selenium is also present in drinking water in some parts of the world and can be added to drinking water as a health measure. Nursing mothers should note that human milk is much richer in selenium than cow’s milk. There is no widely recognized deficiency syndrome for selenium, unlike the syndromes associated with calcium or magnesium (hypocalcemia and hypomagnesemia, respectively). However, many researchers who have investigated Keshan disease (also known as Kashin-Beck disease), a form of heart disease in children, believe that it is caused by selenium deficiency. The disease can be prevented but not cured with supplemental selenium; it responds to treatment with 50 g per day. The symptoms of Keshan disease, which is named for the region of China where it was discovered, include enlargement of the heart and congestive heart failure.
The soil in the Keshan region is low in selenium. The researchers observed that the local Chinese treatKeshan disease with astragalus (Astragalus membranaceus), a plant that absorbs selenium from the soil.
Selenium toxicity was a matter of controversy in the late 2000s. Humans can show symptoms of selenium toxicity after doses as low as 1 mg of sodium selenite, the element’s most common inorganic compound in nature. By contrast, some researchers speculate that the organic forms of selenium may accumulate in the body and interfere with the functioning of sulfur molecules in the body or that they may cause genetic mutations. These longstanding questions await further research. In addition, researchers disagree about how much selenium will produce symptoms of toxicity. It has been suggested that toxicity can result from a daily intake of 2 mg in people who already have body stores of 2.5 mg of selenium or higher. Another measurement suggests that seleniumtoxicity may occur wherever the food or water regularly contains more than 5 to 10 parts per million of selenium. Patients with symptoms of selenium toxicity usually have blood plasma levels of 100 g/dL or higher, which is about four times the upper limit of normal levels. The symptoms of selenium toxicity are not always clearly defined. People living in areas of selenium-rich soil sometimes develop heart, eye, or muscular problems. Eating foods containing high amounts of selenium over a long period of time increases the risk of tooth decay. It is thought that the selenium may compete with the fluoride in teeth, thus weakening their structure. Other symptoms associated with high levels of selenium include a metallic taste in the mouth, garlic-like breath odor, dizziness, nausea, skin inflammation, fatigue, and the loss of hair or nails. The symptoms of acute selenium poisoning include fever, kidney and liver damage, and eventual death.
Selenium is most widely recognized as a substance that speeds up the metabolismof fatty acids and works together with vitamin E (tocopherol) as an antioxidant. Antioxidants are organic substances that are able to counteract the damage done to human tissue by oxidation (the breakdown of fatty acids). Selenium’s antioxidant properties have been studied with respect to several diseases and disorders. In addition, selenium appears to work as an anti-inflammatory agent in certain disorders.
CARDIOVASCULAR DISEASES. Low levels of selenium have been associated with high risk of heart attacks and strokes. It is thought that the antioxidant properties of selenium can help prevent atherosclerosis (narrowing and hardening of the arteries) by decreasing the formation of fatty deposits in the arteries. It does so by soothing the inflamed arterial walls and binding the free radicals that damage the tissues lining the arteries. Other studies indicate that selenium reduces the symptoms of angina pectoris.
CATARACTS. Cataracts contain only one-sixth as much selenium as normal lens tissue. The healthy lens requires adequate levels of three antioxidant enzymes: superoxide dismutase, catalase, and glutathione peroxidase. Glutathione peroxidase in the human eye is dependent on selenium, which suggests that a selenium deficiency speeds up the progression of cataracts.
CANCER. Low dietary levels of selenium have been associated with an increased incidence of cancer. Cancers of the respiratory system and the gastrointestinal tract seem to be especially sensitive to the level of seleniumin the body. In one study, patients with histories of skin cancer were given 200 g of selenium per day. Results indicated that the patients had a reduced incidence of rectal, prostate, and lung cancers as well as a lower rate of mortality from all cancers. In addition, cervical dysplasias (abnormal growths of tissue) in women are associated with low levels of selenium in the women’s diet. In animal studies, as little as 1–4 parts per million of selenium added to the water or food supply is associated with a decreased incidence of cancer. It is not known, however, exactly how selenium protects against cancer. Some researchers believed that it may prevent mutations or decrease the rate of cell division, particularly on the outer surfaces of the body. One study of the effects of a selenium compound on mammary tissue indicated that selenium may inhibit the growth of tumors in deeper layers of tissue, not just cancers arising from the epithelium. Some researchers have explored the possibility that selenium may reduce the risk of prostate cancer. Studies on the question are inconclusive, with the best evidence pointing to the element’s effectiveness among certain groups of men, but not in males in general.
PERIODONTAL DISEASE. Selenium appears to speed up the healing of fragile gum tissue as well as opposing the actions of free radicals, which are damaging to gum tissue.
RHEUMATOID ARTHRITIS. Selenium may be useful for treating several autoimmune diseases, especially Lupus and Rheumatoid arthritis (RA). It has been found that patients suffering from RA have low selenium levels. Selenium is necessary for production of the enzyme glutathione peroxidase, which reduces the production of inflammatory substances in the body (prostaglandins and leukotrienes) as well as opposing free radicals. Although supplemental selenium by itself has not been shown to cause improvement in RA, selenium taken together with vitamin E appears to have measurable positive results.
OSTEOARTHRITIS. Research indicates that selenium is beneficial in the prevention and treatment of osteoarthritis (OA), particularly OA resulting from physical wear and tear or structural problems in the patient’s joints. Selenium supplements are even more effective when given together with vitamins in treating OA.
Selenium is available in topical preparations and as a dietary supplement.
Selenium sulfide for the treatment of dandruff is available as over-the-counter (OTC) scalp preparations or shampoo containing 1% or 2.5% solutions of the drug. A topical 2.5% solution of selenium sulfide is available for the treatment of tinea versicolor. Common trade names include Exsel, Selsun, and Selsun Blue.
Selenium is widely available in vitamin/mineral dietary supplements and in nutritional antioxidant formulas. Although the average diet supplies enough selenium, some naturopaths recommend daily supplements of 100–200g for adults and 30–150g for children. Sexually active males are advised to take higher doses. Some naturopaths recommend taking selenium together with vitamin E on the grounds that their combined effect is greater than the sum of their individual effects. There are no definitive studies on the positive effects on health of selenium taken as a dietary supplement.
Persons using selenium compounds to control dandruff or tinea versicolor should be careful to avoid applying the product to damaged or broken skin. In addition to irritating skin, selenium can enter the body through broken skin. This process, known as percutaneous absorption, can cause selenium toxicity if the preparation is used for a long period of time. Patients should wash their hands carefully after applying the selenium product to affected areas. Doing so will minimize absorption through small breaks in the skin of the hands.
It is difficult to assess the effectiveness of dietary supplements containing selenium because as of the late 2000s there was little agreement on standards for interpreting selenium levels in human blood. Depending on their intake, healthy adults may have blood plasma levels of selenium in the range of 8–25g/dL. In addition, most of the selenium in the body is not carried in the blood but is stored in tissue. Analysis of hair has not been useful in measuring selenium. In the absence of a useful test, people who wish to take supplemental selenium should first find out whether they live in an area that already has high levels of selenium in the drinking water and soil. Most people probably do not need more selenium than is in standard vitamin/ mineral supplements. In addition, the body seems to utilize selenium more efficiently when it is taken together with vitamin E.
The side effects of contact with compounds containing selenium sulfide include stinging of the skin, irritation of the lining of the eyes, hair discoloration or loss, and oily scalp. Both topical products and megadoses of selenium taken by mouth can cause selenium toxicity. The symptoms of selenium toxicity include nausea, vomiting, tiredness, abdominal pain, a garlicky breath odor, and the loss of hair and fingernails. These symptoms usually last 10–12 days after the selenium preparation is discontinued.
Topical preparations containing selenium may interact with the metals in costume jewelry. Patients should remove all their jewelry before applying the shampoo or lotion.