Selenium

Regions of North America identified as low in selenium content are the Northeast, Pacific, Southwest, and coastal plain of the southeastern region of the United States, as well as north central and eastern Canada. The lowest selenium content of soil exists in a few regions of China, especially in Keshan, where severe selenium deficiency was first reported in a human population in 1979. Other areas with low selenium content include parts of Finland and New Zealand. 

A rather narrow dietary intake range exists for selenium, below which deficiency occurs and above which toxicity develops. Only in China have these extremes been shown to relate to the selenium content of the soil.

A dietary intake of approximately 40 mcg of selenium per day seems to be necessary to maintain glutathione peroxidase, an enzyme containing selenium. The diets of practically all nations other than China supply selenium in sufficient amounts to maintain adequate levels of glutathione peroxidase.

Selenium and vitamin E work together synergistically in that they carry out antioxidant and immunostimulating functions better together than individually; however, their mechanisms of action are not the same. Both of these nutrients are part of the "antiaging" or "longevity" group, which may be directly attributable to their antioxidant functions because tissue oxidation by free radicals may be the contributing factor to degenerative disease.

Despite its importance, there is less than 1 mg of selenium in our body, most of it in the liver, kidneys, and pancreas and, in men, in the testes and seminal vesicles. Men have a greater need for selenium, which may function in sperm production and motility. Some selenium is lost through the sperm as well as through the urine and feces. It is absorbed fairly well from the intestines, with an absorption rate of nearly 60 percent.

Selenium content and glutathione peroxidase activity in human breast milk are influenced directly by maternal selenium intake and by the form of selenium consumed. Plasma selenium concentrations of infants fed unsupplemented formula are lower than those of infants fed supplemented formula or human milk.

Major food sources of selenium are Brazil nuts, seafood, kidney, liver, meat and poultry. Fruits and vegetables are low in selenium content. The selenium concentration in foods depends on the selenium content of the soil and water where the food was grown.

Despite a wide range of selenium intakes from food, selenium deficiency is rare in populations throughout the world. Selenium deficiency takes years to develop when food intake is adequate. Selenium deficiency has previously been reported in malnourished patients. Deficient selenium intakes may also contribute to carcinogenesis. Patients with some cancers have been shown to have low serum selenium levels. Patients with cirrhosis have low plasma selenium concentrations, which may predispose them to cancer.

Dietary reference intake

Infants 15-20 mcg/day

Children 20-30 mcg/day

Adolescents 40-55 mcg/day

Adults 55 mcg/day

Pregnant 60 mcg/day

Lactating 70 mcg/day

Selenium content of selected foods

Brazil nuts, 1 oz (543 mcg)

Halibut, baked, ½ fillet (74 mcg)

Tuna, canned, 3 oz (68 mcg)

Oysters, raw, 3 oz (56 mcg)

Rice, white, long grain, 1 cup (44 mcg)

Chicken breast, baked, 3 oz (39 mcg)

Egg noodles, cooked, 1 cup (38 mcg)

Wheat germ, toasted, ¼ cup (28 mcg)

Bagel, 1 (27 mcg)

Sunflower seeds, ¼ cup (25 mcg)

Egg, 1 (16 mcg)

Bread, whole wheat, 1 slice (10 mcg)

Milk, 1 cup (6 mcg)

Deficiency

Keshan disease (cardiomyopathy, that mainly affects children and woman)

Kashan-Beck disease (is common in preadolescent and adolescent children – symmetric stiffness, swelling and pain in the interphalangeal joints of the fingers, followed by generalized osteoarthritis.

Toxicity

Selenosis (skin and nail changes, tooth decay, GI and neurologic abnormalities.