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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.
In addition, Brazil nuts are one of the most concentrated food sources of selenium, featuring about 70-90 micrograms per nut. The reason that we do not include Brazil nuts in the chart that follows as well as in the food sources table at the bottom of this page is that they are not a featured food on our website. (Despite their reputation of being selenium rich, macadamia nuts are not an especially concentrated source of this mineral. Each nut only has about 0.3 mcg.)
For serving size for specific foods, see Nutrient Rating Chart below at the bottom of this page.
What is selenium?
This micromineral is needed in the diet on a daily basis, but only in very small amounts (50 micrograms 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.
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.
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.
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 aren't usually obtained from food, since selenium-rich foods contain about 30-50 micrograms of selenium per serving. (Brazil nuts would be an exception here, since they average about 70-90 micrograms per nut). Selenium supplementation would be a more likely case of selenium toxicity than food ingestion.
In light of potential toxicity risks, the National Academy of Sciences (in the year 2000)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 ¼-inch thick slice, 4-ounce serving of filet mignon beef is broiled, for example, virtually none of the selenium is lost.
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.
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.
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.
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
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.
What foods provide selenium?
It is important to remember that the selenium content of food is highly variable because it depends so heavily on soil conditions. In fact, some researchers have concluded that it is not possible to create a valid list of foods and their selenium content for this very reason. While soil conditions affect plant foods most directly, they also affect animal foods, since most animals depend upon plants for their diet.
Brazil nuts are the most highly concentrated source of selenium. In fact, scientists have shown that a daily Brazil nut is a better source of the mineral than taking a supplement. New Zealand researchers compared Brazil nuts' efficacy to that of selenomethionine supplements in increasing selenium status in 59 New Zealand residents with low selenium (plasma selenium concentrations < 1.27 micro mol/L).
Participants were randomly assigned to one of three groups. One group ate two Brazil nuts each day (estimated to provide approx. 100 micrograms Se). A second group took a supplement providing 100 micrograms of selenium as selenomethionine per day, and the third group, who served as controls, were given a placebo pill. Blood levels of selenium and glutathione peroxidase (GPx - a selenium containing enzyme that is one of the body's most important antioxidants) activities were measured at the beginning of the study and at 2, 4, 8, and 12 weeks.
By week 12, blood levels of selenium had increased by 64.2%, 61.0% and 7.6%, respectively, in the Brazil nut, selenomethionine, and placebo groups. Plasma levels of GPx increased by 8.3%, 3.4% and -1.2%, and whole blood GPx by 13.2%, 5.3% and 1.9% in the Brazil nut, selenomethionine and placebo groups, respectively.
Not only was consumption of two Brazil nuts each day as effective for increasing selenium status and enhancing GPx activity as 100 micrograms of selenomethionine per day, but just one Brazil nut per day would have been sufficient to raise dietary selenium intake to within recommended intake levels for the mineral.
The researchers pointed out that food sources are always preferable to supplementation for improving the nutritional status of a population because they are sustainable, less expensive and have a lower risk of toxicity.
The authors did, however, warn that Brazil nuts are not uniform in their selenium content and may contain much more or much less than the estimated 50 micrograms per nut. No more than one or two Brail nuts should be consumed daily to avoid excessive accumulation of selenium in tissues. (Thomson CD, Chisholm A, et al.,Am J Clin Nutr) Practical Tip: Why take expensive supplements? Enjoy just one Brazil nut each day and ensure your selenium levels remain OK.
Grown or raised under ideal soil conditions, button mushrooms, shiitake mushrooms, cod, shrimp, snapper, tuna, halibut, calf's liver, and salmon are also excellent sources of selenium.
Very good sources of selenium include chicken's eggs, lamb, barley, sunflower seeds, turkey, mustard seeds, and oats.
Introduction to Nutrient Rating System Chart
In order to better help you identify foods that feature a high concentration of nutrients for the calories they contain, we created a Food Rating System. This system allows us to highlight the foods that are especially rich in particular nutrients. The following chart shows the World's Healthiest Foods that are either an excellent, very good, or good source of selenium. Next to each food name, you'll find the serving size we used to calculate the food's nutrient composition, the calories contained in the serving, the amount of selenium contained in one serving size of the food, the percent Daily Value (DV%) that this amount represents, the nutrient density that we calculated for this food and nutrient, and the rating we established in our rating system. For most of our nutrient ratings, we adopted the government standards for food labeling that are found in the U.S. Food and Drug Administration's "Reference Values for Nutrition Labeling." Read more background information and details of our rating system.| World's Healthiest Foods ranked as quality sources of: selenium | ||||||
|---|---|---|---|---|---|---|
| Food | Serving Size | Cals | Amount (mcg) | DV (%) | Nutrient Density | World's Healthiest Foods Rating |
| Crimini mushrooms, raw | 5 oz-wt | 31.2 | 36.85 | 52.6 | 30.4 | excellent |
| Cod, baked/broiled | 4 oz-wt | 119.1 | 53.07 | 75.8 | 11.5 | excellent |
| Shrimp, steamed/boiled | 4 oz-wt | 112.3 | 44.91 | 64.2 | 10.3 | excellent |
| Snapper, baked/broiled | 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 |
| Calf's liver, braised | 4 oz-wt | 187.1 | 57.84 | 82.6 | 7.9 | excellent |
| Mustard seeds | 2 tsp | 35.0 | 9.96 | 14.2 | 7.3 | very good |
| Salmon, chinook, baked/broiled | 4 oz-wt | 261.9 | 53.07 | 75.8 | 5.2 | excellent |
| Egg, 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, cooked | 1 cup | 270.0 | 36.40 | 52.0 | 3.5 | very good |
| Oats, whole grain, cooked | 1 cup | 147.4 | 18.95 | 27.1 | 3.3 | 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 |
| Rye, whole grain, uncooked | 0.33 cup | 188.7 | 19.89 | 28.4 | 2.7 | good |
| Sunflower seeds, raw | 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 |
| Brown rice, 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 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 | 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% |
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
- Abrams CK, Siram SM, Galsim C, et al. Selenium deficiency in long-term total parenteral nutrition. Nutr Clin Pract 1992 7:175-178 1992.
- Badmaev V, Muhammed M, Passwater RA. Selenium: a quest for better understanding. Alt Ther 1996;2(4):59-67 1996.
- Diplock AT. Selenium, antioxidant nutritions, and human diseases. Biol Trac Elem Res. 1992;33:155-156. 1992.
- ESHA Research. Based on data obtained from Food Processor for Windows. Version 7.60, Database version December 2000, ESHA Research, Salem, Oregon 2000.
- Finley JW, Matthys L, Shuler T, et al. Selenium content of foods purchased in North Dakota. Nutr Res 1996;16:723-728 1996.
- 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 1993.
- Groff JL, Gropper SS, Hunt SM. Advanced Nutrition and Human Metabolism. West Publishing Company, New York, 1995 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 1987.
- Mascio PD, Murphy ME, Sies H. Antioxidant defense systems: the role of Carotenoids, tocopherols, and thiols. Am J Clin Nutr 1991;53:194S-200S 1991.
- 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 1976.
- 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 1993.
- National Research Council. Selenium in nutrition. Revised edition. Board on Agriculture, Committee on Animal Nutrition, National Academy of Sciences Press, Washington, DC, 1983 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 1994.
- 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 1994.
- 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 1983.
- 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 1997.
- Thomson CD, Chisholm A, McLachlan SK, Campbell JM. Brazil nuts: an effective way to improve selenium status. Am J Clin Nutr. 2008 Feb;87(2):379-84. 2008. PMID:18258628.
- 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 2003.
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