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Human Body
B Vitamins

Vitamin B12

There are several vitamins. Vitamin B12 is also known as cobalamin and cyanocobalamin and is one of the group of B vitamins.


Active Forms of Vitamin B12:

There are two active forms of vitamin B12:

  • deoxyadenosylcobalamin, and
  • methylcobalamin


Functions of Vitamin B12:

The main functions of vitamin B12 are:

  • Promotes growth, especially healthy growth in children - vitamin B12 is needed for cell division and the production of erythrocytes (i.e. red blood cells)
  • Prevents anaemia - which results from insufficient red blood cells. Pernicious anaemia is sometimes treated with injections of vitamin B12. Symptoms of anaemia can include low energy ranging from mild fatigue to extreme tiredness.
  • Health of nervous system - via maintenance of myelin in the nervous system
  • Synthesis of nucleic acids
  • Correct functioning of Folic Acid (which is also known as vitamin B9)
  • Production of serotonin and dopamine - which affect emotional outlook / "mood" and sleep patterns.
    This function is why increased intake of vitamin B12 may help to alleviate depression and anxiety.
  • Coenzyme for two enzymes:
    1. Methylmalonyl CoA mutase, and
    2. Homocysteine methyltransferase.


Sources of Vitamin B12:

The sources of vitamin B12 come from animals so there are concerns about deficiency in vegans.

  • Liver is an especially good source
  • Meat e.g. beef or pork
  • White fish
  • Eggs (one egg per day is enough for RDA)
  • Milk / Dairy products
  • Brewers Yeast / Yeast Extract
  • Some breakfast cereals are fortified with vitamin B12

Problems due to insufficient or too much Vitamin B12:

Signs of Deficiencies of Vitamin B12

Signs of Excessive Intake of Vitamin B12

  • Affects most body tissues, especially those containing rapidly dividing cells
  • Pernicious anaemia
  • Degeneration of the nervous system (incl. loss of sensation and poor co-ordination)
  • Tongue infections

Although vitamin B12 is not considered toxic, there have been rare reports of allergic reactions to injections of high-doses of vitamin B12.

See also what is a balanced diet? .

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