Vitamin B12 in food

Foods rich in Vitamin B12:

Found only in food of animal origin

• Fishes: standing out in the blues
• Shellfish and derivatives: clam (25 µg) mussel (22 µg), mackerel (10 µg), sardine (15 µg), trout (6,4 µg)
• Liver: may contain 31 to 81 µg of Vitamin B12. Cow and ox being richer
• Egg: chicken egg yolk (4.7µg) and duck egg yolk (5,4µg)
• dairy and cheese: 0.2-3.1 µg

(Values over 100gr of food)

How his deficit manifests itself:

In the blood test: low vitamin B12, larger erythrocytes.
Physically: Anemic symptoms

Other considerations:

Vitamin B12 is essential for functions such as DNA formation, red blood cell growth and tissue regeneration. It is also involved in the metabolism of certain macronutrients. Its deficit is directly associated with a pernicious megaloblastic anemia with symptoms of tiredness, anorexia, pallor, tachycardia, jaundice. Degenerative alterations, mucocutaneas and atherosclerosis may also occur. For the absorption of the food-borne B12 protein, the presence of a gastric mucosal protein called intrinsic factor is necessary, forming the B12-FI complex which will bind to the receptors of the ileum mucosa so that B12 can be absorbed.
It is true that a strict vegetarian diet would imply a deficit of Vitamin B12, but under normal conditions the liver is a good body reserve and its deficit can take years to manifest.
People with atrophic gastritis (common in the elderly) require intramuscular B12, as well as intervened gastric bypass patients.
Pregnant or lactating women have increased Vitamin B12 requirements.