Selenium benefits and side effects

What is selenium and what does selenium do?

In the past, selenium was viewed as a toxin. However, it is now considered an essential trace mineral for humans which means that we need it for survival, but only in small quantities. Selenium is present in organic and inorganic compounds, both of which are good dietary sources of selenium.

Selenium is needed for reproduction, for the proper function of the thyroid glands and for the production of DNA. It protects our body from free radical damage and infections. (1)

Tissues and blood of tuna and some other types of fish are rich in an anti-oxidant compound containing selenium called selenoneine.

Foods high in selenium

FoodServingAmount of Selenium (mcg)% of RDA
for men
Rating% of RDA
for women
Brazil nuts1 oz (28g)537767.1Excellent895Excellent
Oysters3 oysters (140g)107.7153.9Excellent179.5Excellent
Cuttlefish, cooked3 oz (85g)76.2108.8Excellent126.9Excellent
Mussel, cooked3 oz (85g)76.2108.8Excellent126.9Excellent
Octopus, cooked3 oz (85g)76.2108.8Excellent126.9Excellent
Clam, cooked3 oz (85g)54.477.7Excellent90.7Excellent
Swordfish, cooked3 oz (85g)52.474.9Excellent87.4Excellent
Flounder, cooked3 oz (85g)49.570.7Excellent82.5Excellent
Perch, cooked3 oz (85g)47.267.4Excellent78.6Excellent
Abalone, cooked3 oz (85g)4462.9Excellent73.4Excellent
Mackerel, cooked3 oz (85g)43.962.7Excellent73.1Excellent
Snapper, cooked3 oz (85g)41.759.5Excellent69.4Excellent
Grouper, cooked3 oz (85g)39.856.8Excellent66.3Excellent
Halibut, cooked3 oz (85g)39.856.8Excellent66.3Excellent
Herring, cooked3 oz (85g)39.856.8Excellent66.3Excellent
Pollock, cooked3 oz (85g)39.856.8Excellent66.3Excellent
Tuna, cooked3 oz (85g)39.856.8Excellent66.3Excellent
Pork lean, cooked3 oz (85g)38.855.5Excellent64.7Excellent
Lobster, cooked3 oz (85g)36.351.9Excellent60.5Excellent
Salmon, cooked3 oz (85g)34.949.8Excellent58.1Excellent
Haddock, cooked3 oz (85g)34.449.2Excellent57.4Excellent
Crab, cooked3 oz (85g)34.248.8Excellent57Excellent
Shrimp, cooked3 oz (85g)33.748.1Excellent56.1Excellent
Rabbit, cooked3 oz (85g)32.746.7Excellent54.5Excellent
Cod, cooked3 oz (85g)3245.7Excellent53.3Excellent
Egg large2 large (100g)31.645.1Excellent52.7Excellent
Turkey, cooked3 oz (85g)31.344.7Excellent52.1Excellent
Beef liver, cooked3 oz (85g)30.743.8Excellent51.1Excellent
Beef, lean3 oz (85g)30.443.5Excellent50.7Excellent
Crayfish, cooked3 oz (85g)29.141.5Excellent48.5Excellent
Scallops, cooked3 oz (85g)23.733.9Excellent39.5Excellent
Goose, cooked3 oz (85g)21.731Excellent36.1Excellent
Chicken breast filet, cooked3 oz (85g)21.230.4Excellent35.4Excellent
Cheese ricotta, low fat1/2 cup (124g)20.729.6Excellent34.5Excellent
Duck, cooked3 oz (85g)1927.2Excellent31.7Excellent
Quail, cooked3 oz (85g)18.526.5Excellent30.9Excellent
Cheese ricotta1/2 cup (124g)1825.7Excellent30Excellent
Mushrooms, shiitake, cooked1/2 cup (72,5g)1825.7Excellent30Excellent
Sunflower seeds1 oz (28g)1521.4Excellent25Excellent
Carp, cooked3 oz (85g)13.819.7Good23Excellent
Pike, cooked3 oz (85g)13.819.7Good23Excellent
Whole wheat, cooked1/2 cup (50g)1318.5Good21.6Excellent
Trout, cooked3 oz (85g)12.818.2Good21.3Excellent
Soy milk1 cup (250g)11.816.9Good19.7Good
Mushrooms, crimini, raw1/2 cup (43,5g)11.316.1Good18.8Good
Peanuts1 oz (28g)11.316.1Good18.8Good
Rye1 slice (32g)9.914.1Good16.5Good
Veal lean, cooked3 oz (85g)9.914.1Good16.4Good
Milk, cow's1 cup (244g)912.9Good15Good
Bread, mulitgrain1 slice (26g)8.612.3Good14.3Good
Lamb lean, cooked3 oz (85g)8.612.3Good14.3Good
Cheese2 oz (56g)7.811.1Good13Good
Flaxseed1 oz (28g)7.110.1Good11.8Good
Eel, cooked3 oz (85g)7.110.1Good11.8Good
Amaranth, cooked1/2 cup (123g)6.89.6-11.3Good
Barley, cooked1/2 cup (78,5g)6.89.6-11.3Good
Soybeans, cooked1/2 cup (86g)6.39-10.5Good
White rice, cooked1/2 cup (79g)68.5-9.9-
Oats, cooked1/2 cup (117g)5.98.4-9.8-
Coconut meat2 oz (56g)5.68-9.3-
Cashew nuts1 oz (28g)5.68-9.3-
Asparagus, cooked1/2 cup (90g)5.57.9-9.2-
Pinto beans, cooked1/2 cup (85,5g)5.37.6-8.8-
Mustard seeds1 tsp (3g)4.36.1-7.2-
Lima beans, cooked1/2 cup (94g)4.36.1-7.1-
Yogurt low fat1/2 cup (120g)45.7-6.6-
Spelt, cooked1/2 cup (97g)3.95.6-6.5-
Poppy seeds1 oz (28g)3.85.4-6.3-
Mushorroms, white raw1/2 cup (35g)3.34.6-5.4-
Chickpeas, cooked1/2 cup (82g)3.14.4-5.1-
Lentils, cooked1/2 cup (99g)2.83.9-4.6-
Navy beans, cooked1/2 cup (91g)2.73.8-4.4-
Pistachios1 oz (28g)2.63.7-4.3-
Quinoa, cooked1/2 cup (92,5g)2.63.7-4.3-
Coconut water1 cup (240g)2.43.4-4-
Buckwheat, cooked1/2 cup (84g)1.92.6-3.1-
Red cabbage1/2 cup (75g)1.72.4-2.8-
Pumpkin seeds1 oz (28g)1.62.3-2.7-
Sesame seeds1 oz (28g)1.62.3-2.7-
Green peas, cooked1/2 cup (80g)1.52.1-2.5-
Walnuts1 oz (28g)1.42-2.3-
Parsnip, cooked1/2 cup (78g)1.31.9-2.2-
Turnip greens1 cup (144g)1.31.9-2.2-
Bananamedium (118g)1.21.7-2-
Broccoli florets, cooked1/2 cup (78g)1.21.7-2-
Brussels sprouts, cooked1/2 cup (78g)1.21.7-2-
Adzuki beans, cooked1/2 cup (100g)1.21.7-2-
Pecans1 oz (28g)1.11.6-1.8-
Black beans, cooked1/2 cup (86g)1.11.5-1.8-
Kidney beans, cooked1/2 cup (88,5g)1.11.5-1.8-
Macadamia1 oz (28g)11.4-1.7-
Millet, cooked1/2 cup (87g)0.81.1-1.3-
Cocoa powder1 tsp (5g)0.71-1.2-
Almonds1 oz (28g)0.71-1.1-
Hazelnuts1 oz (28g)0.71-1.1-
Wild rice, cooked1/2 cup (82g)0.70.9-1.1-
Beetroot, cooked1/2 cup (85g)0.60.9-1-
Corn, cooked1/2 cup (82g)0.60.9-1-
Kale, cooked1/2 cup (65g)0.60.9-1-
Mung bean sprouts1 cup (100g)0.60.9-1-
For Table Legend & Data Sources Information click here.

Brazil nuts are the best food source of selenium. To see the complete list of health benefits of Brazil nuts click here.

Selenium benefits

Selenium is an antioxidant that works best if combined with vitamin E. It protects the body from free radicals (particles that damage the membranes of the cells) and from DNA damage. This action may be responsible for its protective properties against cancers, ageing and cardiovascular diseases. (2)

  • Selenium benefits related to cancer
    The intake of selenium is associated with a reduced risk of developing bladder and prostate cancers, due to its important anti-cancer properties. (3, 4) . It is believed that these effects derive from selenium’s antioxidant properties and effects on DNA repair, apoptosis (dying of cells) and immune and endocrine systems. (5)
  • Selenium benefits related to cardiovascular diseases
    The antioxidant properties of selenium may play a role in the prevention of cardiovascular diseases. However, more research is needed to prove this link. (6, 7)
  • Selenium benefits related to thyroid
    Selenium is an important component in the production of thyroid hormones and may be beneficial in the treatment of autoimmune thyroid conditions. In Hashimoto’s disease, supplementation of selenium reduces local inflammation, although the progress of this disease cannot be avoided. In Graves’ disease, selenium supplementation helps the thyroid to function normally. (8)
  • Selenium benefits related to immunity
    Selenium can improve some immune functions, such as protection against some pathogens and the immunity response to aging. However, selenium is not useful in the immune reaction to parasites or in the case of allergic asthma. (9)

Selenium deficiency signs and symptoms

Selenium deficiency is rare in the U.S. and many developed countries. Lack of selenium in the soil is often solved by either adding selenium salts to the fertilizers or importing selenium rich staple foods. Selenium deficiency can lead to: (10)

  • Juvenile heart disease also known as Keshan disease which is caused by severed selenium deficiency.
  • A type of osteoarthritis called Kashin-Beck. The symptoms are loss of motion in the joints, pain and swelling. Kashin-Beck is caused by a severe selenium deficiency.
  • Infertility in males.
  • Problems with thyroid (such as goiter), especially in women.
  • Increased iodine deficiency, increasing the risk of cretinism in infants.
  • An increased risk of developing cancers such as bladder, colorectal, esophagus, lung, prostate, skin and stomach. (3)
  • An increased risk of cardiovascular disease. However, more evidence is needed.
  • A decline in brain function. Since the level of blood selenium normally declines with age, elderly people may be in the risk group. The studies on this subject, however, are conflicting. Therefore, more evidence is needed.

Who is at risk of selenium deficiency?

  • Populations in selenium-deficient areas, especially those who eat mostly plant foods, grown in selenium depleted soils (e.g. Finland or some parts of China). (11, 12)
  • People undergoing long term hemodialysis due to dietary restrictions, with the removal of some selenium from the blood and uremia.
  • People with HIV due to inadequate diet, malabsorption and selenium losses through diarrhea.
  • People with malabsorption problems such as in Crohn’s disease or ulcerative colitis.
  • Cigarette smoking, alcohol consumption and oral contraceptives reduce the concentration of selenium in blood and may lead to selenium deficiency in people who are already nutritionally compromised. (2, 13, 14)

Recommended daily intake of selenium (mcg/day)

Life StageAgeRDA for menUL for menRDA for womenUL for women
Infants0-6 months15 (AI)4515 (AI)45
Infants6-12 months20 (AI)6020 (AI)60
Children1-3 years20902090
Children4-8 years3015030150
Children9-13 years4028040280
Adolescents14-18 years5540055400
Adults19-50 years5540055400
Adults51-70 years5540055400
Adults> 70 years5540055400
Pregnancy14-18 years--60-
Pregnancy19-50 years--60-
Breast-feeding14-18 years--70-
Breast-feeding19-50 years--70-
For Table Legend & Data Sources Information click here.

Side effects of excessive selenium

Selenium toxicity is not uncommon and usually occurs form long term consumption of supplements or large amounts of high selenium foods, such as Brazil nuts. (read more..)
The most common symptoms of selenium toxicity are:

  • Early signs are garlic breath odor and metallic taste in the mouth
  • Weakness and fatigue
  • Gastrointestinal disorders (e.g. diarrhea)
  • Hair loss
  • Nail loss, discoloration and brittleness
  • Skin rashes and lesions
  • Bronchial irritation
  • Abnormalities in the nervous system such as peripheral neuropathy
  • Nausea
  • Mottled teeth
  • Irritability

Extremely high levels of selenium may cause:

  • Breathing difficulty
  • Kidney failure
  • Tremors
  • Heart attack
  • Heart failure

Some reports state that long term selenium supplementation (200mcg of selenium per day during 7 years) may increase the risk of diabetes. More studies are required to confirm these findings. (8, 15)

Selenium supplements

You should only take selenium supplements under medical supervision. Selenium supplementation may lead to type 2 Diabetes (more studies are needed to prove this) and interact with certain medications such as Cisplatin.


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