 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
NCP Miracle II
161 Richardson-Bass Rd
Kenly, NC 27542
Tel:(919)284-6002 Fax:(919)284-4197
EMail: info1@ncpmiracle2.com
161 Richardson-Bass Rd
Kenly, NC 27542
Tel:(919)284-6002 Fax:(919)284-4197
EMail: info1@ncpmiracle2.com
| Selenium |
What is selenium?
Selenium is a trace mineral that is essential to good health but required only in small
amounts [1,2]. Selenium is incorporated into proteins to make selenoproteins, which are
important antioxidant enzymes. The antioxidant properties of selenoproteins help prevent
cellular damage from free radicals. Free radicals are natural by-products of oxygen
metabolism that may contribute to the development of chronic diseases such as cancer and
heart disease [2,3]. Other selenoproteins help regulate thyroid function and play a role in
the immune system [4-7].
What foods provide selenium?
Plant foods are the major dietary sources of selenium in most countries throughout the
world. The content of selenium in food depends on the selenium content of the soil where
plants are grown or animals are raised. For example, researchers know that soils in the high
plains of northern Nebraska and the Dakotas have very high levels of selenium. People
living in those regions generally have the highest selenium intakes in the United States (U.
S.) [8]. In the U.S., food distribution patterns across the country help prevent people living
in low-selenium geographic areas from having low dietary selenium intakes. Soils in some
parts of China and Russia have very low amounts of selenium. Selenium deficiency is often
reported in those regions because most food in those areas is grown and eaten locally.
Selenium also can be found in some meats and seafood. Animals that eat grains or plants
that were grown in selenium-rich soil have higher levels of selenium in their muscle. In the
U.S., meats and bread are common sources of dietary selenium [9,10]. Some nuts are also
sources of selenium.
Selenium content of foods can vary. For example, Brazil nuts may contain as much as 544
micrograms of selenium per ounce. They also may contain far less selenium. It is wise to eat
Brazil nuts only occasionally because of their unusually high intake of selenium.
Brazil nuts, dried, unblanched,
Tuna, light, canned in oil, drained
Beef, cooked, 3½ ounces
Spaghetti w/ meat sauce, frozen entrée
Cod, cooked, 3 ounces
Turkey, light meat, roasted, 3½ ounces
Beef chuck roast, lean only, roasted
Chicken Breast, meat only, roasted
Noodles, enriched, boiled
Macaroni, elbow, enriched, boiled
Egg, whole, 1 medium
Oatmeal, instant, fortified, cooked
Rice, white, enriched, long grain, cooked, 1/2 cup
Rice, brown, long-grained, cooked, 1/2 cup
Bread, enriched, whole wheat, commercially prepared, 1 slice
Walnuts, black, dried, 1 ounce
Bread, enriched, white, commercially prepared, 1 slice
Cheddar cheese, 1 ounce
Refer to the U.S. Department of Agriculture's Nutrient Database Web site:
http://www.nal.usda.gov/fnic/cgi-bin/nut_search.pl.
What is the recommended dietary intake for selenium?
Recommendations for selenium are provided in the Dietary Reference Intakes developed by
the Institute of Medicine [12]. Dietary Reference Intakes (DRIs) is the general term for a set
of reference values used for planning and assessing nutrient intake for healthy people.
Three important types of reference values included in the DRIs are Recommended Dietary
Allowances (RDA), Adequate Intakes (AI), and Tolerable Upper Intake Levels (UL). The RDA
recommends the average daily dietary intake level that is sufficient to meet the nutrient
requirements of nearly all (97-98%) healthy individuals in each age and gender group [12].
An AI is set when there is insufficient scientific data available to establish a RDA. AIs meet or
exceed the amount needed to maintain a nutritional state of adequacy in nearly all members
of a specific age and gender group. The UL, on the other hand, is the maximum daily intake
unlikely to result in adverse health effects [12].
There is insufficient information on selenium to establish a RDA for infants. An Adequate
Intake (AI) has been established that is based on the amount of selenium consumed by
healthy infants who are fed breast milk [12]. Table 3 lists the AIs for selenium, in micrograms
(μg) per day, for infants.
Table 2: Adequate Intake for selenium for infants [12]
Age
(months) Males and Females
(μg/day)
0-6 months 15
7-12 months 20
Results of the National Health and Nutrition Examination Survey (NHANES III-1988-94)
indicated that diets of most Americans provide recommended amounts of selenium [13]. The
INTERMAP study examined nutrient intakes of almost 5,000 middle-aged men and women in
four countries in the late 1990s, including the U.S. The primary aim of the study was to
evaluate the effect of dietary micronutrients on blood pressure. Each study participant
completed four, 24-hour dietary recalls, during which they were asked to record everything
consumed (food, beverages, and dietary supplements) over the previous 24 hours.
Selenium intake was lowest among residents of China, the country with the highest known
rate of selenium deficiency. Mean dietary intake of selenium of U.S. participants was 153 μg
for men and 109 μg for women. Both values exceed the recommended selenium intake for
adults and are further evidence of adequate selenium intakes in the U.S. [14]
When can selenium deficiency occur?
Human selenium deficiency is rare in the U.S. but is seen in other countries, most notably
China, where soil concentration of selenium is low [15]. There is evidence that selenium
deficiency may contribute to development of a form of heart disease, hypothyroidism, and a
weakened immune system [16,17]. There is also evidence that selenium deficiency does not
usually cause illness by itself. Rather, it can make the body more susceptible to illnesses
caused by other nutritional, biochemical or infectious stresses [18].
Three specific diseases have been associated with selenium deficiency:
• Keshan Disease, which results in an enlarged heart and poor heart function, occurs in
selenium deficient children.
• Kashin-Beck Disease, which results in osteoarthropathy
• Myxedematous Endemic Cretinism, which results in mental retardation
Keshan disease was first described in the early 1930s in China, and is still seen in large
areas of the Chinese countryside with selenium poor soil [18]. Dietary intake in these areas
is less than 19 micrograms per day for men and less than 13 micrograms per day for women,
significantly lower than the current RDA for selenium [12]. Researchers believe that
selenium deficient people infected with a specific virus are most likely to develop Keshan
disease [18,19].
Selenium deficiency has also been seen in people who rely on total parenteral nutrition
(TPN) as their sole source of nutrition [20,21]. 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 and infused through the IV
line. It is important for TPN solutions to provide selenium in order to prevent a deficiency
[22]. 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 [23]. Gastrointestinal problems that impair selenium
absorption usually affect absorption of other nutrients as well, and require routine
monitoring of nutritional status so that appropriate medical and nutritional treatment can be
provided.
Who may need supplemental selenium?
In the U.S., most cases of selenium depletion or deficiency are associated with severe
gastrointestinal problems, such as Crohn's disease, or with surgical removal of part of the
stomach. These and other gastrointestinal disorders can impair selenium absorption [24-26].
People with acute severe illness who develop inflammation and widespread infection often
have decreased levels of selenium in their blood [27]. Physicians will evaluate individuals
who have gastrointestinal disease or severe infection for depleted blood levels of selenium
to determine the need for supplementation.
People with iodine deficiency may also benefit from selenium supplementation. Iodine
deficiency is rare in the U.S., but is still common in developing countries where access to
iodine is limited [28]. Researchers believe that selenium deficiency may worsen the effects
of iodine deficiency on thyroid function, and that adequate selenium nutritional status may
help protect against some of the neurological effects of iodine deficiency [6,7]. Researchers
involved in the Supplementation en Vitamines et Mineraux AntioXydants (SU.VI.MAX) study
in France, which was designed to assess the effect of vitamin and mineral supplements on
chronic disease risk, evaluated the relationship between goiter and selenium in a subset of
this research population. Their findings suggest that selenium supplements may be
protective against goiter, which refers to enlargement of the thyroid gland [29].
As noted above, selenium supplementation during TPN administration is now routine [21,22].
While specific medical problems such as those described above indicate a need for
selenium supplementation, evidence is lacking for recommending selenium supplements
for healthy children and adults.
Selenium and cancer
Observational studies indicate that death from cancer, including lung, colorectal, and
prostate cancers, is lower among people with higher blood levels or intake of selenium [34-
40]. In addition, the incidence of nonmelanoma skin cancer is significantly higher in areas of
the United States with low soil selenium content [37]. The effect of selenium
supplementation on the recurrence of different types of skin cancers was studied in seven
dermatology clinics in the U.S. from 1983 through the early 1990s. Taking a daily supplement
containing 200 μg of selenium did not affect recurrence of skin cancer, but significantly
reduced the occurrence and death from total cancers. The incidence of prostate cancer,
colorectal cancer, and lung cancer was notably lower in the group given selenium
supplements [41].
Research suggests that selenium affects cancer risk in two ways. As an anti-oxidant,
selenium can help protect the body from damaging effects of free radicals. Selenium may
also prevent or slow tumor growth. Certain breakdown products of selenium are believed to
prevent tumor growth by enhancing immune cell activity and suppressing development of
blood vessels to the tumor [42].
However, not all studies have shown a relationship between selenium status and cancer. In
1982, over 60,000 participants of the Nurse's Health Study with no history of cancer
submitted toenail clippings for selenium analysis. Toenails are thought to reflect selenium
status over the previous year. After three and a half years of data collection, researchers
compared toenail selenium levels of nurses with and without cancer. Those nurses with
higher levels of selenium in their toenails did not have a reduced risk of cancer [43].
Two important long-term studies, the SU.VI.MAX study in France and the Selenium and
Vitamin E Cancer Prevention Trial (SELECT) study in the U.S., are now underway to further
investigate the selenium/cancer prevention link.
The SU.VI.MAX Study is a prevention trial looking at the effects of antioxidant vitamins and
minerals on chronic diseases such as cancer and cardiovascular disease. Doses of the
nutrients provided in the study are one to three times higher than recommended intakes,
including a daily supplement of 100 μg selenium. The SU.VI.MAX study, which began in 1994,
has followed more than 12,000 adult men and women. This study was designed to continue
for eight years, and the research community is eagerly awaiting the results of this study [44].
The SELECT study, a long-term study sponsored by the NIH, is investigating whether
supplemental selenium and/or vitamin E can decrease the risk of prostate cancer in healthy
men. Past evidence as well as pre-clinical trials for the SELECT study suggests that these
two nutrients may be effective in preventing prostate cancer. A daily supplement containing
200 μg of selenium will be given to individuals in the selenium-only study group, while men
in the combined-nutrients group will receive a daily supplement containing 200 μg selenium
and 400 mg vitamin E. The study, which will span from 2001 to 2013, will include 32,400
healthy adult men [45].
Selenium and heart disease
Some population surveys have suggested an association between lower antioxidant intake
and a greater incidence of heart disease [46]. Evidence also suggests that oxidative stress
from free radicals, which are natural by-products of oxygen metabolism, may promote heart
disease [47-49]. For example, it is the oxidized form of low-density lipoproteins (LDL, often
called "bad" cholesterol) that promotes plaque build-up in coronary arteries [48]. 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 [47-49]. Currently there is insufficient
evidence available to recommend selenium supplements for the prevention of coronary
heart disease; however, the SU.VI.MAX study mentioned earlier is looking at the effects of
antioxidant nutrients such as selenium on heart disease.
Selenium and arthritis
Surveys indicate that individuals with rheumatoid arthritis, a chronic disease that causes
pain, stiffness, swelling, and loss of function in joints, have reduced selenium levels in their
blood [50-51]. In addition, some individuals with arthritis have a low selenium intake [52].
The body's immune system naturally makes free radicals that can help destroy invading
organisms and damaged tissue, but that can also harm healthy tissue [53]. Selenium, as an
antioxidant, may help to relieve symptoms of arthritis by controlling levels of free radicals
[54]. Current findings are considered preliminary, and further research is needed before
selenium supplements can be recommended for individuals with arthritis.
Selenium and HIV
HIV/AIDS malabsorption can deplete levels of many nutrients, including selenium. Selenium
deficiency is associated with decreased immune cell counts, increased disease
progression, and high risk of death in the HIV/AIDS population [55,56]. HIV/AIDS gradually
destroys the immune system, and oxidative stress may contribute to further damage of
immune cells. Antioxidant nutrients such as selenium help protect cells from oxidative
stress, thus potentially slowing progression of the disease [57]. Selenium also may be
needed for the replication of the HIV virus, which could further deplete levels of selenium
[58].
An examination of 125 HIV-positive men and women linked selenium deficiency with a higher
rate of death from HIV [59]. In a small study of 24 children with HIV who were observed for
five years, those with low selenium levels died at a younger age, which may indicate faster
disease progression [60]. Results of research studies have led experts to suggest that
selenium status may be a significant predictor of survival for those infected with HIV [61].
Researchers continue to investigate the relationship between selenium and HIV/AIDS,
including the effect of selenium levels on disease progression and mortality. There is
insufficient evidence to routinely recommend selenium supplements for individuals with
HIV/AIDS, but physicians may prescribe such supplements as part of an overall treatment
plan. It is also important for HIV-positive individuals to consume recommended amounts of
selenium in their diet.
What is the health risk of too much selenium?
High blood levels of selenium (greater than 100 μg/dL) can result in a condition called
selenosis [62]. Symptoms of selenosis include gastrointestinal upsets, hair loss, white
blotchy nails, garlic breath odor, fatigue, irritability, and mild nerve damage [2].
Selenium toxicity is rare in the U.S. The few reported cases have been associated with
industrial accidents and a manufacturing error that led to an excessively high dose of
selenium in a supplement [63,64]. The Institute of Medicine of the National Academy of
Sciences has set a tolerable upper intake level (UL) for selenium at 400 micrograms per day
for adults to prevent the risk of developing selenosis [12]. Table 4 lists ULs for selenium, in
micrograms per day, for infants, children, and adults.
Table 4: Tolerable Upper Intake Levels for selenium for infants, children, and adults [12]
Age Males and Females
(μg/day)
0 - 6 months 45
7 - 12 months 60
1-3 y 90
4-8 y 150
9-13 y 280
14-18 y 400
19 y + 400
Selenium is a trace mineral that is essential to good health but required only in small
amounts [1,2]. Selenium is incorporated into proteins to make selenoproteins, which are
important antioxidant enzymes. The antioxidant properties of selenoproteins help prevent
cellular damage from free radicals. Free radicals are natural by-products of oxygen
metabolism that may contribute to the development of chronic diseases such as cancer and
heart disease [2,3]. Other selenoproteins help regulate thyroid function and play a role in
the immune system [4-7].
What foods provide selenium?
Plant foods are the major dietary sources of selenium in most countries throughout the
world. The content of selenium in food depends on the selenium content of the soil where
plants are grown or animals are raised. For example, researchers know that soils in the high
plains of northern Nebraska and the Dakotas have very high levels of selenium. People
living in those regions generally have the highest selenium intakes in the United States (U.
S.) [8]. In the U.S., food distribution patterns across the country help prevent people living
in low-selenium geographic areas from having low dietary selenium intakes. Soils in some
parts of China and Russia have very low amounts of selenium. Selenium deficiency is often
reported in those regions because most food in those areas is grown and eaten locally.
Selenium also can be found in some meats and seafood. Animals that eat grains or plants
that were grown in selenium-rich soil have higher levels of selenium in their muscle. In the
U.S., meats and bread are common sources of dietary selenium [9,10]. Some nuts are also
sources of selenium.
Selenium content of foods can vary. For example, Brazil nuts may contain as much as 544
micrograms of selenium per ounce. They also may contain far less selenium. It is wise to eat
Brazil nuts only occasionally because of their unusually high intake of selenium.
Brazil nuts, dried, unblanched,
Tuna, light, canned in oil, drained
Beef, cooked, 3½ ounces
Spaghetti w/ meat sauce, frozen entrée
Cod, cooked, 3 ounces
Turkey, light meat, roasted, 3½ ounces
Beef chuck roast, lean only, roasted
Chicken Breast, meat only, roasted
Noodles, enriched, boiled
Macaroni, elbow, enriched, boiled
Egg, whole, 1 medium
Oatmeal, instant, fortified, cooked
Rice, white, enriched, long grain, cooked, 1/2 cup
Rice, brown, long-grained, cooked, 1/2 cup
Bread, enriched, whole wheat, commercially prepared, 1 slice
Walnuts, black, dried, 1 ounce
Bread, enriched, white, commercially prepared, 1 slice
Cheddar cheese, 1 ounce
Refer to the U.S. Department of Agriculture's Nutrient Database Web site:
http://www.nal.usda.gov/fnic/cgi-bin/nut_search.pl.
What is the recommended dietary intake for selenium?
Recommendations for selenium are provided in the Dietary Reference Intakes developed by
the Institute of Medicine [12]. Dietary Reference Intakes (DRIs) is the general term for a set
of reference values used for planning and assessing nutrient intake for healthy people.
Three important types of reference values included in the DRIs are Recommended Dietary
Allowances (RDA), Adequate Intakes (AI), and Tolerable Upper Intake Levels (UL). The RDA
recommends the average daily dietary intake level that is sufficient to meet the nutrient
requirements of nearly all (97-98%) healthy individuals in each age and gender group [12].
An AI is set when there is insufficient scientific data available to establish a RDA. AIs meet or
exceed the amount needed to maintain a nutritional state of adequacy in nearly all members
of a specific age and gender group. The UL, on the other hand, is the maximum daily intake
unlikely to result in adverse health effects [12].
There is insufficient information on selenium to establish a RDA for infants. An Adequate
Intake (AI) has been established that is based on the amount of selenium consumed by
healthy infants who are fed breast milk [12]. Table 3 lists the AIs for selenium, in micrograms
(μg) per day, for infants.
Table 2: Adequate Intake for selenium for infants [12]
Age
(months) Males and Females
(μg/day)
0-6 months 15
7-12 months 20
Results of the National Health and Nutrition Examination Survey (NHANES III-1988-94)
indicated that diets of most Americans provide recommended amounts of selenium [13]. The
INTERMAP study examined nutrient intakes of almost 5,000 middle-aged men and women in
four countries in the late 1990s, including the U.S. The primary aim of the study was to
evaluate the effect of dietary micronutrients on blood pressure. Each study participant
completed four, 24-hour dietary recalls, during which they were asked to record everything
consumed (food, beverages, and dietary supplements) over the previous 24 hours.
Selenium intake was lowest among residents of China, the country with the highest known
rate of selenium deficiency. Mean dietary intake of selenium of U.S. participants was 153 μg
for men and 109 μg for women. Both values exceed the recommended selenium intake for
adults and are further evidence of adequate selenium intakes in the U.S. [14]
When can selenium deficiency occur?
Human selenium deficiency is rare in the U.S. but is seen in other countries, most notably
China, where soil concentration of selenium is low [15]. There is evidence that selenium
deficiency may contribute to development of a form of heart disease, hypothyroidism, and a
weakened immune system [16,17]. There is also evidence that selenium deficiency does not
usually cause illness by itself. Rather, it can make the body more susceptible to illnesses
caused by other nutritional, biochemical or infectious stresses [18].
Three specific diseases have been associated with selenium deficiency:
• Keshan Disease, which results in an enlarged heart and poor heart function, occurs in
selenium deficient children.
• Kashin-Beck Disease, which results in osteoarthropathy
• Myxedematous Endemic Cretinism, which results in mental retardation
Keshan disease was first described in the early 1930s in China, and is still seen in large
areas of the Chinese countryside with selenium poor soil [18]. Dietary intake in these areas
is less than 19 micrograms per day for men and less than 13 micrograms per day for women,
significantly lower than the current RDA for selenium [12]. Researchers believe that
selenium deficient people infected with a specific virus are most likely to develop Keshan
disease [18,19].
Selenium deficiency has also been seen in people who rely on total parenteral nutrition
(TPN) as their sole source of nutrition [20,21]. 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 and infused through the IV
line. It is important for TPN solutions to provide selenium in order to prevent a deficiency
[22]. 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 [23]. Gastrointestinal problems that impair selenium
absorption usually affect absorption of other nutrients as well, and require routine
monitoring of nutritional status so that appropriate medical and nutritional treatment can be
provided.
Who may need supplemental selenium?
In the U.S., most cases of selenium depletion or deficiency are associated with severe
gastrointestinal problems, such as Crohn's disease, or with surgical removal of part of the
stomach. These and other gastrointestinal disorders can impair selenium absorption [24-26].
People with acute severe illness who develop inflammation and widespread infection often
have decreased levels of selenium in their blood [27]. Physicians will evaluate individuals
who have gastrointestinal disease or severe infection for depleted blood levels of selenium
to determine the need for supplementation.
People with iodine deficiency may also benefit from selenium supplementation. Iodine
deficiency is rare in the U.S., but is still common in developing countries where access to
iodine is limited [28]. Researchers believe that selenium deficiency may worsen the effects
of iodine deficiency on thyroid function, and that adequate selenium nutritional status may
help protect against some of the neurological effects of iodine deficiency [6,7]. Researchers
involved in the Supplementation en Vitamines et Mineraux AntioXydants (SU.VI.MAX) study
in France, which was designed to assess the effect of vitamin and mineral supplements on
chronic disease risk, evaluated the relationship between goiter and selenium in a subset of
this research population. Their findings suggest that selenium supplements may be
protective against goiter, which refers to enlargement of the thyroid gland [29].
As noted above, selenium supplementation during TPN administration is now routine [21,22].
While specific medical problems such as those described above indicate a need for
selenium supplementation, evidence is lacking for recommending selenium supplements
for healthy children and adults.
Selenium and cancer
Observational studies indicate that death from cancer, including lung, colorectal, and
prostate cancers, is lower among people with higher blood levels or intake of selenium [34-
40]. In addition, the incidence of nonmelanoma skin cancer is significantly higher in areas of
the United States with low soil selenium content [37]. The effect of selenium
supplementation on the recurrence of different types of skin cancers was studied in seven
dermatology clinics in the U.S. from 1983 through the early 1990s. Taking a daily supplement
containing 200 μg of selenium did not affect recurrence of skin cancer, but significantly
reduced the occurrence and death from total cancers. The incidence of prostate cancer,
colorectal cancer, and lung cancer was notably lower in the group given selenium
supplements [41].
Research suggests that selenium affects cancer risk in two ways. As an anti-oxidant,
selenium can help protect the body from damaging effects of free radicals. Selenium may
also prevent or slow tumor growth. Certain breakdown products of selenium are believed to
prevent tumor growth by enhancing immune cell activity and suppressing development of
blood vessels to the tumor [42].
However, not all studies have shown a relationship between selenium status and cancer. In
1982, over 60,000 participants of the Nurse's Health Study with no history of cancer
submitted toenail clippings for selenium analysis. Toenails are thought to reflect selenium
status over the previous year. After three and a half years of data collection, researchers
compared toenail selenium levels of nurses with and without cancer. Those nurses with
higher levels of selenium in their toenails did not have a reduced risk of cancer [43].
Two important long-term studies, the SU.VI.MAX study in France and the Selenium and
Vitamin E Cancer Prevention Trial (SELECT) study in the U.S., are now underway to further
investigate the selenium/cancer prevention link.
The SU.VI.MAX Study is a prevention trial looking at the effects of antioxidant vitamins and
minerals on chronic diseases such as cancer and cardiovascular disease. Doses of the
nutrients provided in the study are one to three times higher than recommended intakes,
including a daily supplement of 100 μg selenium. The SU.VI.MAX study, which began in 1994,
has followed more than 12,000 adult men and women. This study was designed to continue
for eight years, and the research community is eagerly awaiting the results of this study [44].
The SELECT study, a long-term study sponsored by the NIH, is investigating whether
supplemental selenium and/or vitamin E can decrease the risk of prostate cancer in healthy
men. Past evidence as well as pre-clinical trials for the SELECT study suggests that these
two nutrients may be effective in preventing prostate cancer. A daily supplement containing
200 μg of selenium will be given to individuals in the selenium-only study group, while men
in the combined-nutrients group will receive a daily supplement containing 200 μg selenium
and 400 mg vitamin E. The study, which will span from 2001 to 2013, will include 32,400
healthy adult men [45].
Selenium and heart disease
Some population surveys have suggested an association between lower antioxidant intake
and a greater incidence of heart disease [46]. Evidence also suggests that oxidative stress
from free radicals, which are natural by-products of oxygen metabolism, may promote heart
disease [47-49]. For example, it is the oxidized form of low-density lipoproteins (LDL, often
called "bad" cholesterol) that promotes plaque build-up in coronary arteries [48]. 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 [47-49]. Currently there is insufficient
evidence available to recommend selenium supplements for the prevention of coronary
heart disease; however, the SU.VI.MAX study mentioned earlier is looking at the effects of
antioxidant nutrients such as selenium on heart disease.
Selenium and arthritis
Surveys indicate that individuals with rheumatoid arthritis, a chronic disease that causes
pain, stiffness, swelling, and loss of function in joints, have reduced selenium levels in their
blood [50-51]. In addition, some individuals with arthritis have a low selenium intake [52].
The body's immune system naturally makes free radicals that can help destroy invading
organisms and damaged tissue, but that can also harm healthy tissue [53]. Selenium, as an
antioxidant, may help to relieve symptoms of arthritis by controlling levels of free radicals
[54]. Current findings are considered preliminary, and further research is needed before
selenium supplements can be recommended for individuals with arthritis.
Selenium and HIV
HIV/AIDS malabsorption can deplete levels of many nutrients, including selenium. Selenium
deficiency is associated with decreased immune cell counts, increased disease
progression, and high risk of death in the HIV/AIDS population [55,56]. HIV/AIDS gradually
destroys the immune system, and oxidative stress may contribute to further damage of
immune cells. Antioxidant nutrients such as selenium help protect cells from oxidative
stress, thus potentially slowing progression of the disease [57]. Selenium also may be
needed for the replication of the HIV virus, which could further deplete levels of selenium
[58].
An examination of 125 HIV-positive men and women linked selenium deficiency with a higher
rate of death from HIV [59]. In a small study of 24 children with HIV who were observed for
five years, those with low selenium levels died at a younger age, which may indicate faster
disease progression [60]. Results of research studies have led experts to suggest that
selenium status may be a significant predictor of survival for those infected with HIV [61].
Researchers continue to investigate the relationship between selenium and HIV/AIDS,
including the effect of selenium levels on disease progression and mortality. There is
insufficient evidence to routinely recommend selenium supplements for individuals with
HIV/AIDS, but physicians may prescribe such supplements as part of an overall treatment
plan. It is also important for HIV-positive individuals to consume recommended amounts of
selenium in their diet.
What is the health risk of too much selenium?
High blood levels of selenium (greater than 100 μg/dL) can result in a condition called
selenosis [62]. Symptoms of selenosis include gastrointestinal upsets, hair loss, white
blotchy nails, garlic breath odor, fatigue, irritability, and mild nerve damage [2].
Selenium toxicity is rare in the U.S. The few reported cases have been associated with
industrial accidents and a manufacturing error that led to an excessively high dose of
selenium in a supplement [63,64]. The Institute of Medicine of the National Academy of
Sciences has set a tolerable upper intake level (UL) for selenium at 400 micrograms per day
for adults to prevent the risk of developing selenosis [12]. Table 4 lists ULs for selenium, in
micrograms per day, for infants, children, and adults.
Table 4: Tolerable Upper Intake Levels for selenium for infants, children, and adults [12]
Age Males and Females
(μg/day)
0 - 6 months 45
7 - 12 months 60
1-3 y 90
4-8 y 150
9-13 y 280
14-18 y 400
19 y + 400