Vitamin B12: Functions, Sources, Deficiency Symptoms

Vitamin B12 is a water soluble vitamin. It is known as cobalamin because it contains mineral cobalt. it is a unique vitamin, synthesized by only microorganisms and not by animals and plants. It is required for Red blood cell formation, myelin synthesis around neurons, DNA synthesis, and energy production.

How Much Vitamin B12 Required?

  • Up to age of 6 months 0.4 mcg
  • For 7-12 months of age, 0.5 mcg
  • For 1-3 years of age, 0.9 mcg
  • For 4-8 years of age, 1.2 mcg
  • For 9-13 years of age, 1.8 mcg
  • In adults (14+) 2.4 mcg
  • For pregnant female 2.6 mcg
  • And for lactating mother 2.8 mcg

Sources of Vitamin B12

Foods of animal origin are the only natural sources of vitamin B12. The richest sources are liver, kidney, milk, curd, eggs, fish, pork, and chicken.The curd is a better source than milk, due to the synthesis of B12 by Lactobacillus.

Fortified foods (fortified breakfast, nondairy milk, and cereals) Are sources of vitamin B12 for vegans.

Deficiency of Vitamin B12

Symptoms of vitamin B12 deficiency are Anemia (Megaloblastic anemia) Weakness, fatigue, neurological symptoms such as numbness and tingling of fingers and toes, Confusion, memory loss.

Causes of deficiency-
  • Autoimmune destruction of gastric parietal cells
  • Genetic causes
  • Partial or total gastrectomy
  • Insufficient production of IF in older individual
  • Dietary deficiency of Vitamin B1 is seen among the strict vegetarians


Vitamin B12 is administered in therapeutic doses (100-1000 mcg) Intramuscularly. Folic acid administration can also reverse hematological abnormalities observed in B12 deficiency.However, the neurological symptoms persist.Therefore, a combined supplementation of B12 and folate is employed to treat the patients with megaloblastic anemias.


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