General Description
Selenium is a trace mineral required for the manufacture of vital
enzymes, including glutathione peroxidase, the body's premier antioxidant
enzyme. Present in all body tissues, selenium is most concentrated
in the kidneys, liver, spleen, pancreas, and testes.1
Supplemental forms of selenium include inorganic salts, such as
sodium selenite, and organic forms such as selenomethionine and
selenium-rich yeast.
Food sources
Good sources of selenium include wheat germ, Brazil nuts, whole
grains, and seafood. The selenium content of food depends upon
the selenium level of the soil in which it is grown; thus, food
selenium content varies from region to region.
Health applications
Deficiency signs/symptoms
Severe selenium deficiency is associated with Keshan disease,2-4
a serious heart disorder affecting mostly children and women of
child-bearing age, and Kashin-Beck disease, a degenerative arthritic
disorder.5-7 Overt selenium deficiency is
rare, found only in areas with selenium-depleted soil. Subclinical
selenium deficiency, which has been linked to increased risk for
cardiovascular disease, inflammatory conditions, and certain cancers,
is more common.
Antioxidant protection
The primary function of selenium in the human body is to serve
as an activating component of glutathione peroxidase (GPx), the
body's primary antioxidant enzyme. As a component of GPx, selenium
is essential for healthy immune system function and may play a
role in regulating inflammatory response.8-12
GPx is also part of the body's first line of defense against oxidation
of LDL (the "bad" cholesterol). Oxidized LDL is considered a major
contributor to heart disease. Low selenium levels have been linked
to the progression of atherosclerosis,13-17
with severity of the disease parallelling decreased selenium levels.16-17
Cancer prevention
Because GPx is known to be a key factor in immune system function,
many scientists believe that selenium may play a role in cancer
prevention. Low selenium levels have been linked to many types
of cancer including leukemia,18-20 colorectal,
18,21-27 prostate,18,21,27-31 cervical,31,32
ovarian,18,33-37 breast,18,38-42
and lung18,21,43-47 cancers. However, it has
not been determined whether low selenium levels contribute to
cancer development. Some studies suggest that cancers may cause
selenium depletion, rather than the converse.48,49
Dosage/toxicity
As a trace mineral, selenium is only required in small amounts.
Although the U.S. National Research Council has calculated the
RDA for selenium to be 70 and 55 mcg per day for adult men and
women, respectively,3 many nutritionists recommend
a daily intake of 50 to 200 mcg. Intake exceeding 1,000 mcg per
day can result in toxicity. Symptoms of chronic selenium toxicity
include emotional instability, nausea, a garlic odor in the breath
and sweat, and in extreme cases, loss of hair and fingernails.50
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