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Southern Cross Medical Library

The purpose of the Southern Cross Medical Library is to provide information of a general nature to help you better understand certain medical conditions. Always seek specific medical advice for treatment appropriate to you. This information is not intended to relate specifically to insurance or healthcare services provided by Southern Cross. For more articles go to the Medical Library index page.

Vitamin B12 deficiency

Vitamin B12, also called cobalamin, is necessary for the production of red blood cells and plays an important role in maintaining the health of nerve cells and in the formation of genetic material. It is a water-soluble vitamin found in certain foods: meat, fish, milk products and eggs. Vegetables alone are an inadequate source of vitamin B12.
According to a New Zealand Adult Nutrition Survey, 8% of the population may be vitamin B12 deficient.  The survey also revealed inadequate vitamin B12 levels are more common among females than males.
Initial symptoms of vitamin B12 deficiency include dizziness and fatigue. Untreated deficiency can result in anaemia and damage to the nervous system.  Intramuscular vitamin B12 injections form the basis of most treatment plans. 


Vitamin B12 deficiency is most commonly caused by a lack of intrinsic factor - a substance produced in the stomach that is necessary for the absorption of vitamin B12 from food. When intrinsic factor is lacking, vitamin B12 is unable to be absorbed and is therefore unable to be utilised by the body. Pernicious anaemia is one such condition where the production of intrinsic factor is impaired. It is a leading cause of vitamin B12 deficiency.  Other causes of vitamin B12 deficiency include:

  • A diet inadequate in vitamin B12 rich foods - particularly so in vegetarians who don’t eat any animal products, meat, fish, milk, eggs, butter, cheese and other dairy products (vegans)
  • Inadequate absorption or utilisation of B12 because of gastric abnormalities such as coeliac disease, inflammation of the stomach (gastritis), or pancreatic insufficiency
  • Inadequate absorption can also occur after stomach and intestinal surgery as well as in inflammatory bowel diseases like Crohn's disease
  • An increase in certain intestinal organisms 
  • Drugs that may interfere with the absorption of vitamin B12
  • Heavy alcohol consumption
  • Rare congenital disorders.
Research studies have indicated that genetic factors may influence the development of vitamin B12 deficiency in some people.


Symptoms of vitamin B12 deficiency usually don’t appear for at least two years. The reason for this is that a large amount of vitamin B12 is usually stored by the liver. Most people, apart from vegans, have a three to five year supply in their bodies.  Initial symptoms of vitamin B12 deficiency can include: 

  • Dizziness
  • Paleness
  • Shortness of breath
  • Fatigue
  • Anaemia
  • Hearing difficulties.

If left untreated vitamin B12 deficiency can cause progressive damage to the nervous system, especially the nerves outside the brain and spinal cord. When the spinal cord is involved, the first symptoms include difficulty in feeling vibrations in the feet, loss of position sense, and loss of muscle co-ordination (ataxia).  Other symptoms of untreated vitamin B12 deficiency may include:

  • Weight loss
  • An enlarged spleen and liver (hepatosplenomegaly)
  • Exaggerated reflexes
  • Mild depression and confusion
  • Hallucinations, personality and mood changes
  • Irritability
  • Damage to the optic nerve.

Treatment (injections)

Once vitamin B12 deficiency has been diagnosed, the cause of the deficiency must be found. A test that measures the absorption of vitamin B12 (the Schilling test) is used to help detect the underlying cause.
In most cases of vitamin B12 deficiency, intramuscular injections of vitamin B12 (cyanocobalamin) are given. To begin with, regular injections of 1000 micrograms are usually given every week  for 4-6 weeks. This frequency allows the body’s physiology to start producing red cells normally. It also allows the reserves that the liver normally holds to increase.
The injections do not solve the underlying cause of the deficiency and, depending on the underlying cause, it may be necessary to continue having B12 injections for life. It is usually recommended that a maintenance dose of 1000 micrograms is given every three months.
It is recommended that vegans take vitamin B12 supplements or vitamin B12 enriched nutritional yeast. Oral iron supplements can be prescribed if an iron deficiency is also present.
Side effects of vitamin B12 supplementation 
Adverse effects resulting from vitamin B12 supplementation are rare. Hypersensitivity (anaphylaxis) is exceptionally rare and may include swelling, itching, and shock. Very high doses of vitamin B12 may sometimes cause acne. Other uncommon side effects include skin rash, hot flushes, nausea, dizziness and cardiac arrhythmias.
It is important to note that vitamin B12 supplements can be destroyed if taken within an hour of large amounts of vitamin C. Absorption can also be impaired by deficiencies in folic acid, iron or vitamin E. Use of nicotine or excessive alcohol can also deplete vitamin B12 levels.
Improved absorption of vitamin B12 occurs when it is taken with other B vitamins or calcium. Some medications may also cause an increased use or decreased absorption of vitamin B12 (eg: corticosteroids, oral contraceptives, colchicine, proton pump inhibitors).


De Witt, R. S. (2006). Pernicious anaemia. The Gale Encyclopedia of Medicine. Third Edition. Jacqueline L. Longe, Editor. 5 vols. Farmington Hills, MI: Thomson Gale.
Edwards, C.R.W., Bouchier, I.A.D., Haslett, C. & Chilvers, E.R. (eds.). Davidson’s principles and practice of medicine (17th ed.). Edinburgh: Churchill Livingstone.
McGill University Health Centre (2012). Vitamin B12 Deficiency; tracking the genetic causes (Web Page). . [Accessed: 14/09/16]
Rubenstein, Federman et al (Date unknown). Scientific American Medicine. vol 2.
Turner, J. (2005) Vitamin B12. The Gale Encyclopedia of Alternative Medicine. 2nd Edition. Jacqueline L. Longe, Editor. Farmington Hills, MI: Gale Group.
University of Otago and Ministry of Health. 2011. A Focus on Nutrition: Key findings of the 2008/09 New Zealand Adult Nutrition Survey. Chapter 4. Nutrient intakes and dietary sources: Micronutrients. Wellington: Ministry of Health.

Last Reviewed – September 2016


Go to our Medical Library Index Page to find information on other medical conditions.