Selenium – Benefits and Side Effects

A Trace Mineral Anti-Oxidant

I have been hearing about this trace mineral for a few weeks.  So I did some research.  This information came from a National Institutes of Health factsheet.  The NIH’s Office of Dietary Supplements provides information on almost all vitamins and minerals we need.

Here a portion of  the information they give on Selenium.  You can go to their site for more information and see the citations they have used in their research.

Use Selenium in small amounts or you will experience some nasty side effects.

What is selenium?

Selenium is a trace mineral that is essential to good health but required only in small amounts. 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. Other selenoproteins help regulate thyroid function and play a role in the immune system.

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.). 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. 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 selenium content. Selected food sources of selenium are provided in Table 1.

Table 1: Selected Food Sources of Selenium
Food Micrograms
(mcg)
Percent
DV*

Brazil nuts, dried, unblanched, 1 ounce

544

777

Tuna, light, canned in water, drained, 3 ounces

68

97

Cod, cooked, 3 ounces

32

46

Turkey, light meat, roasted, 3 ounces

27

39

Bagel, egg, 4 inch

27

39

Chicken breast, meat only, roasted, 3 ounces

24

34

Beef chuck roast, lean only, roasted, 3 ounces

23

33

Sunflower seed kernels, dry roasted, 1 ounce

23

33

Egg noodles, enriched, boiled, ½ cup

19

27

Macaroni, enriched, boiled, ½ cup

19

27

Ground beef, cooked, broiled, 3 ounces

18

26

Egg, whole, hard-boiled, 1 large

15

21

Oatmeal, instant, fortified, cooked, 1 cup

12

17

Cottage cheese, low fat 2%, ½ cup

11

16

Bread, whole-wheat, commercially prepared, 1 slice

11

16

Rice, brown, long-grain, cooked, ½ cup

10

14

Rice, white, enriched, long-grain, cooked, ½ cup

6

9

Bread, white, commercially prepared, 1 slice

6

9

Walnuts, black, dried, 1 ounce

5

7

Cheddar cheese, 1 ounce

4

6

*DV = Daily Value. DVs are reference numbers developed by the Food and Drug Administration (FDA) to help consumers determine if a food contains a lot or a little of a specific nutrient. The DV for selenium is 70 micrograms (mcg). Most food labels do not list a food’s selenium content. The percent DV (%DV) listed on the table indicates the percentage of the DV provided in one serving. A food providing 5% of the DV or less is a low source while a food that provides 10–19% of the DV is a good source. A food that provides 20% or more of the DV is high in that nutrient. It is important to remember that foods that provide lower percentages of the DV also contribute to a healthful diet. For foods not listed in this table, please refer to the U.S. Department of Agriculture’s Nutrient Database Web site.

What is the recommended dietary intake for selenium?

Recommendations for selenium are provided in the Dietary Reference Intakes developed by the Institute of Medicine. 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. 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. Table 2 lists the RDAs for selenium, in micrograms (mcg) per day, for children and adults.

Table 2: Recommended Dietary Allowances (RDA) for Selenium for Children and Adults
Age
(years)
Males and Females
(mcg/day)
Pregnancy
(mcg/day)
Lactation
(mcg/day)

1–3

20

N/A

N/A

4–8

30

N/A

N/A

9–13

40

N/A

N/A

14–18

55

60

70

19+

55

60

70

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. There is evidence that selenium deficiency may contribute to development of a form of heart disease, hypothyroidism, and a weakened immune system. 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.

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

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. People with acute severe illness who develop inflammation and widespread infection often have decreased levels of selenium in their blood. 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. 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. 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.

As noted above, selenium supplementation during TPN administration is now routine. 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 supplements
Selenium occurs in staple foods such as corn, wheat, and soybean as selenomethionine, the organic selenium analogue of the amino acid methionine. Selenomethionine can be incorporated into body proteins in place of methionine, and serves as a vehicle for selenium storage in organs and tissues. Selenium supplements may also contain sodium selenite and sodium selenate, two inorganic forms of selenium. Selenomethionine is generally considered to be the best absorbed and utilized form of selenium.

Selenium is also available in ‘high selenium yeasts’, which may contain as much as 1,000 to 2,000 micrograms of selenium per gram. Most of the selenium in these yeasts is in the form of selenomethionine. This form of selenium was used in the large scale cancer prevention trial in 1983, which demonstrated that taking a daily supplement containing 200 micrograms of selenium per day could lower the risk of developing prostate, lung, and colorectal cancer. However, some yeast may contain inorganic forms of selenium, which are not utilized as well as selenomethionine.

A study conducted in 1995 suggested that the organic forms of selenium increased blood selenium concentration to a greater extent than inorganic forms. However, it did not significantly improve the activity of the selenium-dependent enzyme, glutathione peroxidase. Researchers are continuing to examine the effects of different chemical forms of selenium, but the organic form currently appears to be the best choice.

What are some current issues and controversies about selenium?

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. In addition, the incidence of non-melanoma skin cancer is significantly higher in areas of the United States with low soil selenium content. Taking a daily supplement containing 200 mcg 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.

Research suggests that selenium might affect 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.

Selenium and heart disease
Some population surveys have suggested an association between lower antioxidant intake and a greater incidence of heart disease. Evidence also suggests that oxidative stress from free radicals, which are natural by-products of oxygen metabolism, may promote heart disease. For example, it is the oxidized form of low-density lipoproteins (LDL, often called “bad” cholesterol) that promotes plaque build-up in coronary arteries. 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. Currently there is insufficient evidence available to recommend selenium supplements for the prevention of coronary 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. In addition, some individuals with arthritis have a low selenium intake.

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. Selenium, as an antioxidant, may help to relieve symptoms of arthritis by controlling levels of free radicals. 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. 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. Selenium also may be needed for the replication of the HIV virus, which could further deplete levels of selenium.

What is the health risk of too much selenium?

Blood levels of selenium greater than 100 mcg/d can result in a condition called selenosis.

Symptoms of selenosis include gastrointestinal upsets, hair loss, white blotchy nails, garlic breath odor, fatigue, irritability, and mild nerve damage.

Selenium toxicity is rare in the U.S.

 

Selenium and Healthful Diets

The federal government’s 2010 Dietary Guidelines for Americans notes that “nutrients should come primarily from foods. Foods in nutrient-dense, mostly intact forms contain not only the essential vitamins and minerals that are often contained in nutrient supplements, but also dietary fiber and other naturally occurring substances that may have positive health effects. …Dietary supplements…may be advantageous in specific situations to increase intake of a specific vitamin or mineral.”

Gary

About Gary

I am retired, but not tired. I still want to be valuable to others. I know that others are valuable to me. After looking back on six decades, I have asked myself this question: “What do I believe?” My mind filled up. My heart started beating faster. My spirit soared. I post blogs to share what my mind is working on, what my heart believes would help others and, what my spirit is communicating to me. What do I believe, you ask? Decisions dictate your path In love, not hate In tolerance, not prejudice In health, not sickness In wealth, not poverty In kindness, rudeness In happiness, not sadness In encouragement, not discouragement In faith, not doubt In courage, not fear I have been and will be challenged in each one of these beliefs, but the biggest belief is to stay positive and not turn negative. This belief helps me maintain all of the others.

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