Selenium Health Article

Description

Selenium is a nonmetallic element with an atomic number of 34 and an atomic weight of 78.96. Its chemical symbol is Se. Selenium is most commonly found in nature in its inorganic form, sodium selenite. An organic form of selenium, selenomethionine, is found in foods.

General use

The role of selenium in human nutrition and other therapeutic applications has provoked intense controversy over the past two decades. In contrast to such major minerals as magnesium and calcium, neither selenium's benefits nor its toxic aspects are yet fully understood. Until very recently, selenium was considered a toxic element that was not necessary to human health. In 1989, 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. There is less than 1 mg of selenium in the average human body. The selenium is concentrated in the liver, kidneys, and pancreas. In males, selenium is also found in the testes and seminal vesicles. Selenium currently has a variety of applications, ranging from standard external preparations for skin problems to experimental and theoretical applications in nutrition and internal medicine.

Alternative medicine

Naturopaths use selenium supplements to treat asthma, acne, tendinitis, infertility problems 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.

Dermatology

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. When selenium is compounded with sulfur to form a sulfide, it has antibiotic and antifungal properties. Selenium sulfide 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.

Nutrition

Prior to 1989, there were no established RDA values for selenium. In 1989, the National Research Council of the National Academy of Sciences defined the RDAs for selenium as follows: Males aged 15–18 years, 50 g; 19–24 years, 70 g; 25–50 years, 70 g; 51 years and older, 70 g. Females: aged 15–18 years, 50 g; 19–24 years, 55 g; 25–50 years, 55 g; 51 years and older, 55 g; pregnant, 65 g; lactating, 75 g. The generally higher levels for males are related to the importance of selenium in producing vigorous sperm.

The amount of selenium in the diet is influenced by its level in the soil. Most selenium is absorbed from food 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 sperm. Selenium levels in soil vary widely, not only in different countries but also across different regions. For example, in the United States the western states have higher levels of selenium in the soil than the eastern states. South Dakota has the highest rates of soil selenium in the United States, while Ohio has the lowest.

Foods that are high in selenium contain the element in an organic form, selenomethionine. This form of selenium is considerably less toxic than inorganic sodium selenite 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, 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 treat Keshan disease with astragalus (Astragalus membranaceus), a plant that absorbs selenium from the soil.

Selenium toxicity is still a matter of controversy. It is a known fact that humans can tolerate higher levels of selenium in its organic form (selenomethionine) than in its inorganic forms. Humans can show symptoms of selenium toxicity after doses as low as 1 mg of sodium selenite. On the other hand, 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 long-term 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 selenium toxicity may occur wherever the food or water regularly contains more than 5 or 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.