11.

Vitamin B12

Vitamin B12 deficiency occurs when a lack of vitamin B12 causes the body to produce abnormally large red blood cells that cannot function properly.
Vitamin B12 is involved in producing red blood cells, maintaining a healthy nervous system, and converting food to energy. It also helps to regulate the immune system and mood, and control levels of the amino acid homocysteine, elevated levels of which are associated with heart disease.

Symptoms of Vitamin B12 Deficiency
Vitamin B12 performs several important functions in the body, including keeping the nervous system healthy.

A deficiency in this vitamin can cause a wide range of problems, including:
•    extreme tiredness 
•    a lack of energy 
•    pins and needles (paraesthesia)
•    a sore and red tongue 
•    mouth ulcers 
•    muscle weakness 
•    disturbed vision 
•    psychological problems, which may include depression and confusion  
•    problems with memory, understanding and judgement 

Treating Vitamin B12 Deficiency 
Vitamin B12 deficiency can be easily treated with injections to replace the missing vitamins.
Vitamin B12 supplements are usually given by injection at first. 
Adult dose- 1 mg every week for 1 month then 1mg once every 1–3 months, by intramuscular injection.