Selenium is an essential micronutrient (i.e., a substance the body needs only in very small quantities). It is found in trace amounts in certain foods. 


What does selenium do? 

  • Its antioxidant properties help it protect the body’s cells from free radicals, which contribute to the development of certain diseases such as cancer (notably prostate, colorectal, and lung cancer) and cardiovascular diseases;
  • It slows the aging process and certain metabolic cell disorders;
  • It slows the aging process and certain metabolic cell disorders;
  • It plays a key role in testosterone synthesis (the male sex hormone) and the formation of healthy sperm;
  • It stimulates the immune system.

Selenium is also believed to be effective in preventing cataracts and numerous viral diseases. 


Since the body does not synthesize selenium, we have to get it from food or supplements, if necessary.2 

Recommended Dietary Allowances for Selenium 

Age Group
Adequate Intake in µg/Day)
0 to 6 months
7 to 12 months
ChildrenAges 1 to 3
Ages 4 to 839
PreteensAges 9 to 1340
TeensAges 14 to 1855
AdultsAge 19 and older55
Pregnant women 60 
Nursing mothers 70

Source: Food and Nutrition Board, Institute of Medicine, Dietary Reference Intakes for Vitamin C, Vitamin E, Selenium, and Carotenoids, 2000. Multi-Vitamin/Mineral Supplement Monograph, 0ct. 2007.

**Lacking sufficient scientific evidence, authorities have established adequate intake (AI) amounts rather than recommended dietary allowances (RDAs).

Adequate selenium intake is based on observed average intakes in North American babies in good health.


Selenium enters the food chain through plants that draw this mineral from the soil. Wheat cultivated in North America is a good source of selenium. In Canada all farm animals are given a selenium supplement in their feed (excluding producing dairy cows). 

Food Sources for Selenium: 

  • Meats, seafood, and grains (depending on the selenium content of the soil where they are grown);
  • Brazil nuts are very rich in selenium. A single nut contains the recommended daily allowance of selenium.

Because of their high fat content, Brazil nuts can easily go rancid so choose nuts still in their brown skin to reduce the risks of buying rancid nuts 

Shell the nuts yourself or buy small quantities of shelled nuts from a store with fast stock turnover. You can store them in the freezer. 

Animal and vegetal food's source
Portion Size
Brazil nuts, dried
5g (1 nut)
Pacific oysters, raw or steamed
100g (3½oz)
(2-4 medium)
Tuna, canned
100g (3½oz)
Turkey or chicken giblets, braised
100g (3½oz)
Atlantic herring, marinated
100g (3½oz)
Clams, canned
100g (3½oz)
(13 medium)
Shiitake mushrooms, dried
10 mushrooms (36g)
Pork chops, cooked
100g (3½oz)
Tuna, halibut, cod, redfish, plaice, swordfish, and salmon, baked or grilled
100g (3½oz)
Crab or lobster, steamed or boiled
100g (3½oz)
Salmon, baked or canned
100g (3½oz)
Turkey, dark meat, roasted
100g (3½oz)
Shrimp, raw or cooked
100g (3½oz)
Beef, outside round, braised
100g (3½oz)
Lamb, shoulder, braised
100g (3½oz)
Domestic duck, roasted
100g (3½oz)
Regular ham (11% fat), roasted
100g (3½oz)
Egg, poached
1 large
Whole wheat bread
1 tranche (34g)
Brown long grain rice, cooked
125ml (1/2 cup)

Source: Health Canada, Canadian Nutrient File, versions 2001b and 2005; *U.S. Department of Agriculture (USDA), National Nutrient Database for Standard Reference.


Generally, selenium deficiency occurs only in the following cases: 

  • In people who mainly eat foods from regions where the soil contains little selenium (e.g., China);
  • In people fed parenterally using a formula not enriched with selenium for an extended period of time;
  • people suffering from serious intestinal diseases such as Crohn’s disease or ulcerative colitis.

Very minor deficiency may be associated with a variety of illnesses such as heart or inflammatory diseases, asthma, weakened immune system, cancer, cataracts, etc. 

Exact selenium needs for seniors are not well known, and the current recommended dietary allowances are derived from those established for young adults. It is critical that seniors ensure that they are getting enough selenium in their diet because it is suspected that a selenium deficiency may increase the risk of anemia.  

Signs of selenium deficiency: 

  • Weakness and loss of muscle mass;
  • Slight decrease in fertility in men;
  • Higher cholesterol level;
  • Change in thyroid gland function;
  • Weak immune system.

Adverse effects

Canadian and U.S. authorities have established the tolerable upper intake level of selenium at 400 µg a day for adults. Doses of 1,000 µg a day are considered toxic. 

Signs of excess selenium:  

  • Hair loss;
  • White spots on nails;
  • Brittle nails;
  • Skin problems;
  • Breath has garlicky odor;
  • Metallic taste in mouth;
  • Feelings of fatigue, irritability, and nausea.


  • Selenium allergy (rare);
  • People suffering from goiter (supplement not recommended).

*If you are pregnant or breastfeeding, selenium supplements are not recommended. Selenium intake from food is sufficient. 


Natural health products or vitamin supplements:  

  • none (Selenium’s beneficial antioxidant effects could be combined with those of certain supplements and plants); 


  • Antacids1 may reduce selenium absorption;
  • Prolonged use of high doses of corticosteroids may reduce the level of selenium in the blood.

Additional information

1If you take a selenium supplement, take it either one hour before or two hours after taking these medications. 

2Speak with your pharmacist if you plan to take selenium supplements. Your pharmacist can help you choose the solution that’s best for you based on your health and any drugs you take.