selenium

What can high-selenium foods do for you?

  • Protect cells from free-radical damage
  • Enable your thyroid to produce thyroid hormone
  • Help lower your risk of joint inflammation

What events can indicate a need for more high-selenium foods?

  • Weakness or pain in the muscles
  • Discoloration of the hair or skin
  • Whitening of the fingernail beds

Excellent sources of selenium include button mushrooms, shiitake mushrooms, cod, shrimp, snapper, tuna, halibut, calf's liver, and salmon.

 

Description

What is selenium?

This micromineral is needed in the diet on a daily basis, but only in very small amounts (50 milligrams or less). The other microminerals that all humans must get from food are arsenic, boron, cobalt, copper, chromium, fluorine, iodine, iron, manganese, molybdenum, nickel, silicon, vanadium, and zinc.

In the case of selenium, the amount needed from food is actually measured in micrograms, and ranges from 20-70 micrograms. (A microgram is one thousandth of a milligram, and in one ounce, there are about 30 million micrograms.)

While the nutritional value of all plant food depends on the soil in which it was grown, the selenium content of plants seems particularly sensitive to soil concentrations. For this reason, most of the early research on selenium focused on diseases in sheep, cattle, turkeys, and pigs which involved low soil concentrations of selenium and insufficient amounts of selenium in the forage plants eaten by these animals.

How it Functions

What is the function of selenium?

Prevention of oxidative stress

Although humans have to breathe oxygen to stay alive, oxygen is a risky substance inside the body because it can make molecules overly reactive. When oxygen-containing molecules become too reactive, they can start damaging the cell structures around them. In chemistry, this imbalanced situation involving oxygen is called oxidative stress.

Selenium helps prevent oxidative stress by working together with a group of nutrients that prevent oxygen molecules from becoming too reactive. This group of nutrients includes vitamin E, vitamin C, glutathione, selenium, and vitamin B3.

In many instances of heart disease, for example, where oxidative stress has been shown to be the source of blood vessel damage, low intake of selenium has been identified as a contributing factor to the disease. Similarly, in rheumatoid arthritis, where oxidative stress damages the area inside and around the joints, dietary deficiency of selenium has been show to be a contributing cause.

Support of the thyroid gland

In addition to iodine, selenium is a critical mineral for maintaining proper function of the thyroid gland. In order for the thyroid to produce the most active form of its hormone (a version of thyroid hormone that is called T3), selenium is not only essential, but also helps regulate the amount of hormone that is produced.

Cancer prevention

Accumulated evidence from prospective studies, intervention trials and studies on animal models of cancer have suggested a strong inverse correlation between selenium intake and cancer incidence. Several mechanisms have been suggested to explain the cancer-preventive activities of selenium. Selenium has been shown to induce DNA repair and synthesis in damaged cells, to inhibit the proliferation of cancer cells, and to induce their apoptosis, the self-destruct sequence the body uses to eliminate worn out or abnormal cells. In addition, selenium is incorporated at the active site of many proteins, including glutathione peroxidase, which is particularly important for cancer protection. One of the body's most powerful antioxidant enzymes, glutathione peroxidase is used in the liver to detoxify a wide range of potentially harmful molecules. When levels of glutathione peroxidase are too low, these toxic molecules are not disarmed and wreak havoc on any cells with which they come in contact, damaging their cellular DNA and promoting the development of cancer cells.

Deficiency Symptoms

What are deficiency symptoms for selenium?

Deficiency symptoms for selenium are difficult to determine and controversial in the research literature. Intake of selenium that is borderline or only mildly deficient has not been connected with specific symptoms in the research literature. With prolonged and severe deficiency, symptoms clearly center around two of the body areas where oxidative stress is known to take its toll: the heart and the joints.

With respect to the heart, there is actually a specific disease, called Keshan disease, which can be prevented by increased intake of selenium. This disease involves heart arrhythmias and loss of heart tissue. With respect to the joints, there is also a specific disease, called Kashin-Beck's disease, in which selenium deficiency has been determined to be a primary contributing cause. This disease involves deterioration of the joint tissue.

When severe selenium deficiency is accompanied by severe overall malnutrition, symptoms can include weakness or pain in the muscles, discoloration of the hair or skin, and whitening of the fingernail beds.

Toxicity Symptoms

What are toxicity symptoms for selenium?

Nausea, vomiting, hair loss, skin lesions, abnormalities in the beds of the fingernails, and fingernail loss can all be symptomatic of selenium toxicity. Levels of selenium necessary to trigger these toxicity symptoms cannot be obtained from food, however, but only from selenium supplementation.

However, because of the toxicity risk at high levels of supplementation, in 2000 the National Academy of Sciences set a tolerable upper limit (UL) for selenium of 400 micrograms per day for men and women 19 years and older.

Impact of Cooking, Storage and Processing

How do cooking, storage, or processing affect selenium?

Like most minerals, selenium is present in many different forms in food, and can vary greatly in its response to cooking and processing. In some foods, where a greater percent of selenium is found in water-soluble form and contact with water is great, high losses of selenium can occur. For example, when navy beans are cooked, 50% of the original selenium is lost.

The processing of wheat is another example of the susceptibility of selenium to substantial loss. In 60% extraction wheat flour - the kind that is used to make over 90% of all breads, baked goods, and pastas sold in the U.S., almost 75% of the original selenium is lost.

In the case of animal foods, loss of selenium from cooking appears minimal. When a -inch thick slice, 4-ounce serving of filet mignon beef is broiled, for example, virtually none of the selenium is lost.

Factors that Affect Function

What factors might contribute to a deficiency of selenium?

Dietary deficiency is the most common cause of selenium deficiency. Because plant content of selenium is so heavily dependent on the selenium content of the soil, researchers have been able to identify different areas of the world where selenium deficiency is particularly common.

For example, several areas of Africa, Russia, New Zealand, and China have been identified as high-risk selenium deficiency areas. In the United States, parts of the Pacific Northwest, parts of the Great Lakes region moving eastward toward the New England states, and parts of the Atlantic Coast have also been identified as selenium-deficient regions. Living in these regions and eating foods grown within them could contribute to risk of selenium deficiency.

Drug-Nutrient Interactions

What medications affect selenium?

Glucocorticoids are a widely-used family of anti-inflammatory drugs based on a prototype substance called cortisol. In the United States, cortisol-based anti-inflammatory drugs are available under 70 different brand names. Many of these medications are based on one of the three major cortisol subtypes that consist of prednisolone, dexamethasone, and triamcinolone. All of these medications can reduce the body's supply of selenium.

Nutrient Interactions

How do other nutrients interact with selenium?

Selenium is indirectly responsible for keeping the body's supply of at least three other nutrients intact: these three other nutrients are vitamin C, glutathione, and vitamin E. Although the chemistry of these relationships is complicated, it centers around an enzyme (protein molecule in the body that helps "jump start" a chemical reaction) called glutathione peroxidase. This enzyme cannot function without selenium.

Both iron deficiency and copper deficiency appear to increase the risk of selenium deficiency.

Health Conditions

What health conditions require special emphasis on selenium?

Selenium may play a role in the prevention and/or treatment of the following health conditions:
  • Acne
  • Asthma
  • Cervical dysplasia
  • Colorectal cancer
  • Esophageal cancer
  • HIV/AIDS
  • Infertility (male)
  • Kashin-Beck's disease
  • Keshan's disease
  • Multiple sclerosis
  • Ovarian cysts
  • Parkinson's disease
  • Periodontal disease
  • Psoriasis
  • Rheumatoid arthritis
  • Senile cataracts
  • SIDS (sudden infant death syndrome)
  • Stomach cancer

Form in Dietary Supplements

What forms of selenium are found in dietary supplements?

Selenium can be purchased as a dietary supplement in one of two basic forms: chelated or non-chelated. "Chelated" means connected with another molecule. In the case of selenium, the most common chelates fall into the category of amino acid chelates. The most widely-available are selenomethionine and selenocysteine.

Supplemental selenium is also available in non-chelated form. Here the most widely available choices are sodium selenate and sodium selenite. Although all forms of selenium described above are fairly well absorbed by the body, some studies show a slight edge to selenomethionine over selenocysteine, selenocysteine over sodium selenate, and sodium selenate over sodium selenite.

Selenized yeast is a more food-like form of selenium also available in supplemental form.

Food Sources

Introduction to Nutrient Rating System Chart

The following chart shows the foods which are either excellent, very good or good sources of this nutrient. Next to each food name you will find the following information: the serving size of the food; the number of calories in one serving; DV% (percent daily value) of the nutrient contained in one serving (similar to other information presented in the website, this DV is calculated for 25-50 year old healthy woman); the nutrient density rating; and the food's World's Healthiest Foods Rating. Underneath the chart is a table that summarizes how the ratings were devised. For more detailed information on our Nutrient Rating System, please click here.

 

Foods Ranked as quality sources of:
selenium
Food Serving
Size
Cals Amount
(mcg)
DV
(%)
Nutrient
Density
World's
Healthiest
Foods Rating
Mushrooms, Crimini, Raw 5 oz-wt 31.2 36.85 52.6 30.4 excellent
Cod, Pacific, Fillet, Baked, Broiled 4 oz-wt 119.1 53.07 75.8 11.5 excellent
Shrimp, MixedSpecies, Steamed, Boiled 4 oz-wt 112.3 44.91 64.2 10.3 excellent
Snapper, Baked 4 oz-wt 145.2 55.57 79.4 9.8 excellent
Tuna, Yellowfin, Baked/Broiled 4 oz-wt 157.6 53.07 75.8 8.7 excellent
Halibut, Baked/Broiled 4 oz-wt 158.8 53.07 75.8 8.6 excellent
Liver, Calf 4 oz-wt 187.1 57.84 82.6 7.9 excellent
Seeds, Mustard 2 tsp 35.0 9.96 14.2 7.3 very good
Chinook Salmon Fillet-Baked/Broiled 4 oz-wt 261.9 53.07 75.8 5.2 excellent
Egg, Hen, Whole, Boiled 1 each 68.2 13.55 19.4 5.1 very good
Turkey Breast, Roasted 4 oz-wt 214.3 33.00 47.1 4.0 very good
Lamb, loin, roasted 4 oz-wt 229.1 34.36 49.1 3.9 very good
Barley 1 cup 270.0 36.40 52.0 3.5 very good
Oats, Whole Grain 1 cup 145.1 18.95 27.1 3.4 very good
Chicken Breast, Roasted 4 oz-wt 223.4 28.01 40.0 3.2 good
Tofu, Raw 4 oz-wt 86.2 10.09 14.4 3.0 good
Beef Tenderloin, Lean Broiled 4 oz-wt 240.4 27.67 39.5 3.0 good
Sunflower Seeds, Dried 0.25 cup 205.2 21.42 30.6 2.7 good
Garlic 1 oz-wt 42.2 4.03 5.8 2.5 good
Rice, Long Grain Brown, Cooked 1 cup 216.4 19.11 27.3 2.3 good
Venison 4 oz-wt 179.2 14.63 20.9 2.1 good
Blackstrap Cane Molasses 2 tsp 32.1 2.43 3.5 1.9 good
Asparagus, Boiled 1 cup 43.2 3.06 4.4 1.8 good
Spinach (boiled, with salt) 1 cup 41.4 2.70 3.9 1.7 good
Mozzarella Cheese, Part Skim, Shredded 1 oz-wt 72.1 4.08 5.8 1.5 good
World's Healthiest
Foods Rating
Rule
excellent DV>=75% OR Density>=7.6 AND DV>=10%
very good DV>=50% OR Density>=3.4 AND DV>=5%
good DV>=25% OR Density>=1.5 AND DV>=2.5%

Public Health Recommendations

What are current public health recommendations for selenium?

Adequate Intake (AI) levels for selenium, set in 2000 by the Institute of Medicine at the National Academy of Sciences, are as follows:

  • Males and females, 0-6 months: 15 micrograms
  • Males and females, 6-12 months: 20 micrograms

Recommended Dietary Allowances for selenium, set in 2000 by the Institute of Medicine at the National Academy of Sciences, are as follows:

  • Males and females, 1-3 years: 20 micrograms
  • Males and females, 4-8 years: 30 micrograms
  • Males and females, 9-13 years: 40 micrograms
  • Males and females, 14 years and older: 55 micrograms
  • Pregnant females: 60 micrograms
  • Lactating females: 70 micrograms

References

  • Abrams CK, Siram SM, Galsim C, et al. Selenium deficiency in long-term total parenteral nutrition. Nutr Clin Pract 1992 7:175-178.
  • Badmaev V, Muhammed M, Passwater RA. Selenium: a quest for better understanding. Alt Ther 1996;2(4):59-67.
  • Diplock AT. Selenium, antioxidant nutritions, and human diseases. Biol Trac Elem Res. 1992;33:155-156.
  • ESHA Research. Based on data obtained from Food Processor for Windows. Version 7.60, Database version December 2000, ESHA Research, Salem, Oregon.
  • Finley JW, Matthys L, Shuler T, et al. Selenium content of foods purchased in North Dakota. Nutr Res 1996;16:723-728.
  • Ge K, Yang G. The epidemiology of selenium deficiency in the etiological study of endemic diseases in China. Am J Clin Nutr 1993;57:259S-263S.
  • Groff JL, Gropper SS, Hunt SM. Advanced Nutrition and Human Metabolism. West Publishing Company, New York, 1995.
  • Lane HW, Lotspeich CA, Moore CE, et al. The effect of selenium supplementation on selenium status of patients receiving chronic total parenteral nutrition. JPEN 1987;11:177-182.
  • Mascio PD, Murphy ME, Sies H. Antioxidant defense systems: the role of Carotenoids, tocopherols, and thiols. Am J Clin Nutr 1991;53:194S-200S.
  • Meiners CR, Derise NL, Lau HC, et al. (1976). The content of nine mineral elements in raw and cooked mature dry legumes. J Arg Food Chem 1976;24:1126-1130.
  • Moriarty PM, Picciano MF, Beard J, et al. Iron deficiency decreases Se-GPX mRNA level in the libver and impairs selenium utilization in other tissues. FASEB J 1993;7:A277.
  • National Research Council. Selenium in nutrition. Revised edition. Board on Agriculture, Committee on Animal Nutrition, National Academy of Sciences Press, Washington, DC, 1983.
  • Nishiyama S, Futagoishi-Suginohara Y, Matsukura M, et al. Zinc supplementation alters thyroid hormone metabolism in disabled patients with zinc deficiency. J Am Coll Nutr 1994;13:62-67.
  • Olin KL, Walter RM, Keen CL. Copper deficiency affects selenoglutathione peroxidase and selenodeiodinase activities and antioxidant defense in weanling rats. Am J Clin Nutr 1994;59:654-658.
  • Pedersen B, Eggum BO. The influence of milling on the nutritive value of flour from cereal grains. Part 2. Wheat. Qual Plant Plant Fds Hum Nutr 1983;33:51-61.
  • Stone J, Doube A, Dudson D, et al. Inadequate calcium, folic acid, vitamin E, zinc, and selenium intake in rheumatoid arthritis patients: results of a dietary survey. Semin Arth Rheum 1997;27(3):180-185.
  • Vogt, T. M. Ziegler, R. G. Graubard, B. I et al. Serum selenium and risk of prostate cancer in U.S. blacks and whites. Int J Cancer. 2003 Feb 20; 103(5):664-70.

© 2002 The George Mateljan Foundation