Is Vitamin B12 Deficiency Dangerous?

Health and Nutrition

Vitamin B12 is a water-soluble B vitamin. At the centre of the molecule of vitamin B12 is an atom of cobalt and hence the name cobalamin. The compounds with vitamin B₁₂ activity are collectively called “cobalamins”. The cyanocobalamin form is used in supplements and is found in trace amounts in food (1).

Is deficiency of vitamin B12 dangerous?


Unlike other B vitamins, vitamin B12 losses from the body are small and that small amount is through stools. Most of the B12 vitamin released into the digestive tract is again reabsorbed. It was found that only 0.1 % of vitamin B12 is lost from our body stores every day (2). 


That is the reason why B12 deficiency is not seen immediately even though the diet is lacking in vitamin B12.  If our body stores of vitamin B12 are good it could be years before the deficiency signs are seen even on a B12 deficient diet.


But if deficiency does set it can have some serious consequences especially if it is not detected early and corrected.


Pernicious anaemia


The deficiency of vitamin B12 leads to pernicious anaemia (macrocytic megaloblastic anaemia). The main reason for this type of anaemia is the involvement of vitamin B12 in folate metabolism and synthesis of DNA (2). 


In pernicious anaemia the red blood cells (RBCs) under microscope look large and immature. The other reason for pernicious anaemia is the lack of intrinsic factor in the gastric juice which is essential for absorption of vitamin B12 (3).


Pernicious anaemia symptoms (2, 3, 4)


  • Weakness
  • Lethargy
  • Constipation
  • Loss of appetite


Affects nervous system


Vitamin B12 deficiency causes destruction of myelin sheath of the nerve cells. This leads to problems with nervous system (2).


  • Nerve impulse conduction problems
  • Paralysis and it may become fatal


Because of nervous system being affected following symptoms may be seen


  • Back pain
  • Tingling sensation in legs and feet
  • Depression
  • Confusion
  • Dementia (decline in memory)
  • Redness of mouth and tongue
  • Unsteadiness and issues with maintaining balance


Neurological symptoms are seen at a later stage of deficiency and usually develop after the onset of anaemia (5). 


Because of balance issue the risk of falling and fracture of bones also increases.


Cardiovascular disease


Elevated levels of homocysteine a sulphur containing amino acid which is derived from methionine is an independent risk factor for cardiovascular disease. Vitamin B12 along with folic acid and vitamin B₆ is involved in homocysteine metabolism. 


In a study it was observed that hyper-homocysteinemia was common enough and was due to low vitamin B 12 concentration as they did not find any case of subnormal serum folic acid level (6).


When there is a deficiency of vitamin B12 the homocysteine levels increase in the blood. It is very important for our heart health to take recommended dietary allowance of vitamin B12 (4).


Vitamin B12 is very important for every age


Vitamin B12 deficiency has been linked to age-related vision problems and risk of frailty. Both are major risk factors for disability in the elderly. For pregnant women also vitamin B12 is very important as low levels of vitamin B12 has been linked to higher risk of neural tube defect in babies (1). 


Severe cobalamin deficiency early in life may affect psychoeducational functioning through adolescence (7).


Some of the deficiency consequences are serious in nature and can be dangerous if not corrected.


Final word

The signs and symptoms of vitamin B12 usually appear before there is any permanent damage to the nervous system. Especially anaemia is seen much before any serious damage is done. Catch vitamin B12 deficiency in early stages and avert any substantial damage that can occur.




  1. O’Leary, F. and Samman, S. (2010) Vitamin B12 in health and disease. Nutrients. Vol. 2(3).


  1. Wildman, R. (2009) The Nutritionist-Food, Nutrition, and Optimal Health, Vitamins are vital molecules in food 191. Routledge, Taylor and Francis Group, Second Edition.   New York and London.


  1. Yeung, D. and Laquarta, I. (2003) Heinz Handbook of Nutrition, Vitamins 109, Ninth Edition. Distributed by H.J. Heinz Company.


  1. National Institute of Health, Office of Dietary Supplements (2019). Vitamin B12.


  1. Ralapanawa, D. M., Jayawickreme, K. P., Ekanayake, E. M. and Jayalath, W. A. (2015) B12 deficiency with neurological manifestations in the absence of anaemia, BMC research notes. Vol. 8 (458).


  1. Raina, S. K., Chahal, J. S. and Kaur, N. (2015) Correlation between homocysteine and Vitamin B12 levels: A post-hoc analysis from North-West India, Int J Health Allied Sci. Vol.4 (2).;year=2015;volume=4;issue=2;spage=115;epage=118;aulast=Raina


  1. Black, M. M. (2008) Effects of vitamin B12 and folate deficiency on brain development in children, Food and nutrition bulletin. Vol. 29 (2 Suppl).


Leave a Reply

Your email address will not be published. Required fields are marked *

Your email address will not be published.Required fields are marked *

Looks good!
Please Enter Your Comment
Looks good!
Please Enter Your Name
Looks good!
Please Enter Your valid Email Id