that oral selenium supplements that increase the plasma
selenium concentration result in higher sperm motility.
Description
At least 11 selenoproteins have been discovered to
date, with evidence suggesting that many more exist.
They are found in cell membranes, blood, organs,
prostategland and testicles. They include:
Glutathione peroxidases (GPx). Four have been
identified: classical or cellular GPx, plasma or extrac-
ellular GPx, phospholipid hydroperoxide GPx, and
gastrointestinal GPx. They are all antioxidant
enzymes that reduce ROS, such as hydrogen perox-
ide and lipid hydroperoxides, to harmless products
like water and alcohols.
Thioredoxin reductase. This enzyme maintains thio-
redoxins, proteins that act as antioxidants, in the form
required to properly regulate cell growth and viability.
Iodothyronine deiodinases. Three of these have been
identified. These selenoproteins are essential enzymes
for normal development, growth, and the regulation
of thyroid hormones. The thyroid gland releases very
small amounts of biologically active thyroid hormone
(T3) and larger amounts of an inactive form of thyroid
hormone (T4) into the circulation. Most T3 is created
by the removal of one iodine atom from T4 in a
reaction made possible by iodothyronine deiodinases.
Selenoprotein P (SeP). This one is found in plasma
and in the cells that line the inner walls of blood
vessels. It is believed to function as a transport pro-
tein, as well as an antioxidant capable of protecting
cells from damage by RNS.
Selenoprotein W (SeW). SeW is found in muscle. Its
function is presently unknown, but it is believed to
play a role in muscle metabolism.
Selenophosphate synthetase. This enzyme is required
to incorporate the special selenocysteine amino acid
when selenoproteins are made (protein biosynthesis).
The richest food sources of selenium are Brazil
nuts, organ meats and fish, followed next by muscle
meats. As for plants and grains, there is a wide varia-
tion in their selenium content because it depends on
the selenium content of the soil in which they grow.
For example, Brazil nuts grown in areas of Brazil with
selenium-rich soil provide more selenium than those
grown in a selenium-poor soil. In the United States,
grains are a good source of selenium, but not fruits and
vegetables. However, people living in areas with low
soil selenium avoid deficiency because they eat foods
produced in areas with higher soil selenium. It appears
that selenium from different sources is absorbed by the
body with varying efficiency. For example, a recent
study showed that the mean absorption of selenium
from fish was 85–90%, compared with 50% from
yeast. Some good food sources of selenium include
(per 1oz–serving or as indicated):
Brazil nuts from Brazil( 544 mg)
Fish (cod, shellfish, flounder, tuna)(10–20mg)
Eggs ( 14 mg per egg, whole)
Organ and muscle meats (8–12mg)
Turkey, chicken (7–11mg)
Long–grained brown rice ( 7 mg per cup)
Walnuts ( 5 mg)
Cheddar cheese ( 5 mg)
Oatmeal, bran (3–4mg per cup)
Garlic (0.25mg/g)
Enriched noodles, macaroni, white rice ( 10 mg per cup)
The Recommended Dietary Allowance (RDA) for
selenium is:
Infants: There is insufficient information on sele-
nium to establish a RDA for infants.
Children (1–3 y): 20mg
Children (4–8 y): 30mg
Children (9–13 y): 40mg
Adolescents (14–18): 55mg
Adults: 55mgSeleniumRecommended Dietary
Age Allowance (mcg)
Children 1–3 yrs. 20
Children 4–8 yrs. 30
Children 9–13 yrs. 40
Adolescents14–18 yrs. 55
Adults 19 yrs. 55
Pregnant women 60
Breastfeeding women 70
Selenium
Food (mcg)
Brazil nuts (from Brazil), 1 oz. 544
Egg, 1 whole 14
Fish (cod, shellfish, tuna) 1 oz. 10-20
Enriched noodles or macaroni, 1 cup 10
Rice, white, 1 cup 10
Organ and muscle meat, 1 oz. 8-12
Turkey or chicken, 1 oz. 7-11
Rice, brown, long-grain, 1 cup 7
Cheddar cheese, 1 oz. 5
Walnuts, 1 oz. 5
Oatmeal or bran, 1 cup 3-4
Garlic, 1 oz. 0.25
mcg microgram(Illustration by GGS Information Services/Thomson Gale.)
Selenium