  What foods provide selenium?
Plant foods are the major dietary sources of selenium in most countries throughout the
world. The amount of selenium in soil, which varies by region, determines the amount of selenium in the plant foods that are
grown in that soil.
Researchers know
that soils in the high plains of northern Nebraska & the Dakotas have very high levels of selenium. People living
in those regions generally have the highest selenium intakes in the US.6
Soils in some
parts of China & Russia have very low amounts of selenium & dietary selenium deficiency is often reported in those
regions.
Selenium also can be found in some meats
& seafood. Animals that eat grains or plants that were grown in selenium-rich soil have higher levels of
selenium in their muscle.
In the US,
meats & bread are common sources of dietary
selenium.7, 8 Some nuts, in particular Brazil nuts & walnuts, are also very good sources of selenium. The table of food sources
of selenium suggests many dietary sources of selenium.
What is the Recommended Dietary Allowance for selenium
for adults? The
Recommended Dietary Allowance (RDA) is the average daily dietary intake level that is sufficient to meet the nutrient requirements
of nearly all (97-98%) individuals in each life-stage & gender group.9 The 2000 RDAs for
selenium for adults,9 in micrograms (mcg), are:
|
Life-Stage |
Men |
Women |
Pregnancy |
Lactation |
|
Ages 19 + |
55 mcg |
55 mcg |
|
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|
All ages |
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60 mcg |
70 mcg |
|
Results of the Total Diet Study, a national survey conducted by the U.S. Food
& Drug Administration (1982-86), indicated that the diets of most adult men & women provide recommended amounts of
selenium. 10 |
When can selenium deficiency occur?
Selenium deficiency
is most commonly seen in parts of China where the selenium content in the soil & therefore selenium intake, is very low.
Selenium deficiency is linked to Keshan Disease. The most common signs of selenium deficiency seen
in Keshan Disease are an enlarged heart & poor heart function.11 Keshan disease
has been observed in low-selenium areas of China, where dietary intake is less than 19 mcg per day for men & less than
13 mcg per day for women (12). This intake is significantly lower than the current RDA for selenium.
Selenium deficiency
also may affect thyroid function because selenium is essential for the synthesis of active thyroid hormone. 4
Researchers also believe selenium deficiency may worsen the effects of iodine deficiency on thyroid
function & that adequate selenium nutritional status may help protect against some of the neurologic effects of iodine
deficiency.5
Selenium
deficiency has been seen in people who rely on total parenteral nutrition (TPN) as their sole source of nutrition. 13, 14
TPN is
a method of feeding nutrients through an intravenous (IV) line to people whose digestive systems do not function. Forms of
nutrients that do not require digestion are dissolved in liquid & infused through the IV line. It's important for TPN
solutions to provide selenium in order to prevent a deficiency.15
Physicians
can monitor the selenium status of individuals receiving TPN to make sure they are receiving adequate amounts.
Severe
gastrointestinal disorders may decrease the absorption of selenium, resulting in selenium depletion or deficiency.16 Gastrointestinal problems that impair selenium absorption usually affect absorption of other nutrients as
well & require routine monitoring of nutritional status so that physicians can recommend appropriate treatment.16
Table of Food Sources of Selenium
The selenium content of foods varies according to the growing area. The following table lists the mean
selenium content of foods identified in the Total Diet Study 45 & in the USDA data bank.
46
|
Food |
Micro-grams |
% DV* |
|
Brazil nuts, dried, unblanched, 1 oz |
840 |
1200 |
|
Tuna, canned in oil, drained, 3 1/2 oz |
78 |
111 |
|
Beef / calf liver, 3 oz |
48 |
69 |
|
Cod, cooked, dry heat, 3 oz |
40 |
57 |
|
Noodles, enriched, boiled, 1 c |
35 |
50 |
|
Macaroni and cheese (box mix), 1 c |
32 |
46 |
|
Turkey, breast, oven roasted, 3 1/2 oz |
31 |
44 |
|
Macaroni,elbow, enriched, boiled, 1 c |
30 |
43 |
|
Spaghetti w/ meat sauce, 1 c |
25 |
36 |
|
Chicken, meat only, 1/2 breast |
24 |
34 |
|
Beef chuck roast, lean only, oven roasted, 3 oz |
23 |
33 |
|
Bread, enriched, whole wheat, 2 slices |
20 |
29 |
|
Oatmeal, 1 c cooked |
16 |
23 |
|
Egg, raw, whole, 1 large |
15 |
21 |
|
Bread, enriched, white, 2 slices |
14 |
20 |
|
Rice, enriched, long grain,cooked, 1 c |
14 |
20 |
|
Cottage cheese, lowfat 2%, 1/2 c |
11 |
16 |
|
Walnuts, black, dried, 1 oz |
5 |
7 |
|
Cheddar cheese, 1 oz |
4 |
6 |
|
*DV = Daily Value. DVs are reference numbers based on the Recommended Dietary Allowance (RDA). They were developed
to help consumers determine if a food contains very much of a specific nutrient. The DV for selenium is 70 micrograms (mcg).
The percent DV (%DV) listed on the nutrition facts panel of food labels tells adults what percentage of the DV is provided
by one serving. Even foods that provide lower percentages of the DV will contribute to a healthful diet. |
*DV = Daily Value. DVs are reference numbers based on the Recommended Dietary Allowance (RDA). They were developed
to help consumers determine if a food contains very much of a specific nutrient.
The DV for selenium is 70 micrograms (mcg). The percent DV (%DV) listed on the nutrition facts panel of food
labels tells adults what percentage of the DV is provided by one serving.
Even foods that provide lower percentages of the DV will contribute to a healthful diet.
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selenium - you are here!
Who may need extra selenium?
Selenium
supplementation is essential for anyone relying on TPN as the sole source of nutrition & selenium supplementation has
become routine during TPN administration since the relationship between selenium deficiency & TPN was discovered.15
Gastrointestinal
disorders such as Crohn's disease can impair selenium absorption. Most cases of selenium depletion or deficiency are associated
w/severe gastrointestinal problems, such as in individuals who have had over half of their small intestines surgically removed.17
A
physician, who will determine the need for selenium supplementation, should evaluate individuals who have gastrointestinal
disease & depleted blood levels of selenium.18
What are some current issues &
controversies about selenium?
Selenium & cancer
Some studies indicate that mortality (death) from cancer, including lung, colorectal & prostate
cancers, is lower among people w/higher selenium blood levels or intake.19-25 Also, the
incidence of nonmelanoma skin cancer is significantly higher in areas of the US w/low soil selenium levels.22
The effect of selenium supplementation on the recurrence of these types of skin cancers was studied
in 7 dermatology clinics in the US from 1983 through the early 1990's.
Supplementation w/200 mcg selenium daily
did not affect recurrence of skin cancer, but significantly reduced total mortality & mortality from cancers. In addition,
incidence of prostate cancer, colorectal cancer & lung cancer was lower in the group given selenium supplements.26
However, not all studies have shown a relationship between selenium status & cancer.
In 1982, over 60,000 participants of the Nurses Health Study w/no history of cancer submitted toenail clippings for selenium
analysis.
Toenail analysis is thought to reflect
selenium status over the previous year. After 3 1/2 years, researchers compared the toenail selenium levels of nurses w/ &
w/out cancer. They did not find any apparent benefit of higher selenium levels.27
These conflicting results emphasize the need for additional
research on the relationship between selenium & chronic diseases such as cancer. A study that may help answer some of
the questions about the effect of selenium supplementation on cancer risk has started in France. The Supplementation en Vitamines
et Mineraux AntiXydants, or SU.VI.MAX Study, is a prevention trial that is providing doses of antioxidant vitamins & minerals
that are 1 to 3 times higher than recommended intakes, including a daily supplement of 100 mcg selenium.
More than
12,000 men & women are being followed for 8 years to determine the effect of supplementation on the incidence of chronic
disease, such as cancers & cardiovascular disease. 28
Selenium & heart disease
Some population surveys have indicated an association between a lower antioxidant intake w/a
greater incidence of heart disease.29 Additional lines of evidence suggest that oxidative stress from free radicals may promote heart
disease.30
e.g., it's the oxidized form of low-density
lipoproteins (LDL, often called "bad" cholesterol) that promotes plaque build-up in coronary arteries.31
Selenium is one of a group of antioxidants
that may help limit the oxidation of LDL cholesterol and thereby help to prevent coronary artery disease.30, 32 Currently there's insufficient evidence available to recommend selenium supplements for the prevention
of coronary heart disease.
Selenium & arthritis
Surveys of patients w/rheumatoid arthritis, a chronic disease that causes pain, stiffness, swelling
& loss of function in joints, have indicated that they have reduced selenium levels in their blood.33, 34
In addition, some individuals w/arthritis
have a low selenium intake.35
The body's immune system naturally makes free radicals
that can help destroy invading organisms & damaged tissue, but that can also harm healthy tissue.36
Selenium, as an antioxidant, may help
control levels of free radicals & help to relieve symptoms of arthritis.37 Current
findings are considered preliminary & further research is needed before selenium supplements can be recommended for individuals
w/arthritis.
Selenium & HIV
HIV / AIDS related malabsorption can deplete levels of many nutrients. Selenium deficiency is
commonly associated w/HIV/AIDS & has been associated w/a high risk of death from this disease. 38,
39
Of 24 children w/HIV who were observed
for 5 years, those w/low selenium levels died at a younger age, which may indicate faster disease progression.40 An examination of 125 HIV positive men & women also associated selenium deficiency w/mortality.39 Researchers believe that selenium may be important in HIV disease because of its role in the
immune system & as an antioxidant.
Selenium also may be needed for the replication
of the HIV virus, which could deplete host levels of selenium.38 Researchers are actively
investigating the role of selenium in HIV/AIDS & see a need for clinical trials that evaluate the effect of selenium supplementation
on HIV disease progression. 41
What is the health risk of too much selenium? There's a moderate
to high health risk of too much selenium. High blood levels of selenium can result in a condition called selenosis.42
Symptoms
includeL
- gastrointestinal
upsets
- hair loss
- white blotchy
nails
- mild nerve
damage
Selenium
toxicity is rare in the US & the few reported cases have been associated w/industrial accidents & a manufacturing
error that led to an excessively high dose of selenium in a supplement.43, 44
The Institute
of Medicine has set a tolerable upper intake level for selenium at 400 micrograms per day for adults to prevent the risk of
developing selenosis. "Tolerable upper intake levels represent the maximum intake of a nutrient that is likely to pose no
risk of adverse health effects in almost al individuals in the general population."9
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