Vitamin B12 (cobalamin) is a water soluble vitamin. It can only be absorbed in conjunction with intrinsic factor, a type of protein secreted by the stomach. 


What does vitamin B12 do? 

Vitamin B12 plays a key role in: 

  • Growth;
  • Cell division;
  • q Proper functioning of the body’s cells;
  • Balancing the nervous system;
  • Synthesizing DNA, RNA, protein, and myelin (a substance that coats some nerve fibers);
  • Producing red blood cells;
  • Producing and breaking down carbohydrates and lipids.

Together with vitamins B6 and B9, vitamin B12 helps prevent cardiovascular disease by limiting the formation of a sulfur-based amino acid that causes arterial and venous vascular accidents (homocysteine) in blood. 


Recommended Dietary Allowance for Vitamin B12: 

Amount (µg* per day)
0 to 6 months
7 to 12 months
1 to 3 years
4 to 8 years
9 to 13 years
14 years and up
Pregnant women
Nursing mothers

Source:; Food and Nutrition Board, Institute of Medicine, Dietary Reference Intakes for Thiamin, Riboflavin, Niacin, Vitamin B6, Folate, Vitamin B12, Pantothenic Acid, Biotin, and Choline, 2000. This data reflects a consensus between Canadian and U.S. health authorities.

*µg = microgram = 1 millionth of a gram

**Due to a lack of sufficient scientific evidence, authorities have established adequate intake (AI) amounts rather than recommended dietary allowances (RDAs). The adequate intake for vitamin B12 is based on observed average intakes in North American babies in good health.


Vitamin B12 is naturally present mostly in foods of animal origin. Many processed foods are enriched with vitamin B12. 

Food Sources for Vitamin B12: 

Portion Size
Vitamin B12 (µg*)
Tinned clams
100g (3½oz) (13 medium)
Cooked beef liver
100g (3½oz)
71µg to 83µg
Braised lamb, turkey, and veal testicles and liver
100g (3½oz)
37µg to 77µg
Clam and tomato cocktail
125ml (1/2 cup)
Boiled octopus
100g (3½oz)
Raw or steamed Pacific oysters
100g (3½oz) (2 to 4 medium)
16µg to 28µg
Sautéed or braised veal brains
100g (3½oz)
10µg to 21µg
Steamed crab
100g (3½oz)
7µg to 12µg
Grilled tuna
100g (3½oz)
Stewed poultry giblets
100g (3½oz)
Tinned sardines (bone-in)
100g (3½oz) (8 medium)
Tinned, baked, grilled, or smoked salmon
100g (3½oz)
4µg to 6µg
Baked or grilled rainbow trout
100g (3½oz)
Pickled herring
100g (3½oz)
Cooked beef and veal, all parts
100g (3½oz)
2µg to 4µg
Tinned tuna
100g (3½oz)
2µg to 4µg
Raw egg yolk
30g to 60g (2 to 4 yolks)
Baked swordfish
100g (3½oz)
Steamed shrimp
100g (3½oz)
Braised lamb, all parts
100g (3½oz)

Source: www.passeportsanté.net; Health Canada, Canadian Nutrient File, versions 2001b and 2005; United States Department of Agriculture (USDA), National Nutrient Database for Standard Reference.

*µg = microgram = 1 millionth of a gram


Vitamin B12 deficiency is difficult to diagnose as the body’s cobalamin reserves are quite high thanks to the liver, which retains them for long periods of time. The symptoms of deficiency may therefore take a number of months or even years to appear. 

Vitamin B12 deficiency is often caused by poor absorption. Because vitamin B12 must bond with intrinsic factor, which is secreted by the stomach, to be absorbed, it must first be separated via gastric acidity from food proteins. Vitamin B12 absorption is compromised if one of these two steps does not take place or is slowed down. 

Particular care should be taken by: 

  • People with pernicious anemia (Biermer’s anemia), because they do not secrete intrinsic factor, which is crucial to absorbing vitamin B12;
  • People who have had their ileum (part of the intestine) removed;
  • The elderly, who may have trouble absorbing vitamin B12 due to low gastric acidity;
  • Vegans and vegetarians. Pregnant or nursing vegan women must take care to include an appropriate amount of vitamin B12 in their diets.

Signs of vitamin B12 deficiency: 

  • Fatigue;
  • Weakness;
  • Shortness of breath;
  • Nausea;
  • Constipation and flatulence;
  • Loss of appetite, weight loss;
  • Neurological symptoms such as tingling and numbness of the extremities, difficulty walking;
  • Mood swings;
  • Memory loss and dementia.

Adverse effects

No harmful effects have been observed among healthy individuals who ingest excessive amounts of vitamin B12 through food or supplements. The low apparent toxicity of this vitamin may result from the fact that only a small amount of vitamin B12 is absorbed through the digestive tract, even when large doses are taken orally. 

Signs of excess vitamin B12: 

  • None. 

NOTE: Very high doses may aggravate acne.


  • None at normal doses;
  • People who have suffered a heart attack or who are at a high risk of cardiovascular disease, as high doses taken over an extended period of time may increase the risk of recurrence for cardiovascular disorders and even death.


Natural health products or vitamin supplements: 

  • Folic acid (may mask a vitamin B12 deficiency);
  • Potassium supplements may decrease the absorption of vitamin B12.


  • All antacids (they reduce the absorption of vitamin B12 from food sources, but not from supplements);
  • Medications that lower blood sugar levels may reduce the absorption of vitamin B12 (milk or a calcium carbonate supplement may cancel out this effect);
  • Medications used to treat gout;
  • Anti-cholesterol medications;
  • Some antibiotics.

Additional information

Speak with your pharmacist if you plan to take vitamin B12 supplements. Your pharmacist can help you choose the solution that’s best for you based on your health and any drugs you take. 

Other names

Vitamin B12, Cobalamin