What are the reasons for Vitamin B₁₂ Deficiency?

Health and Nutrition

Vitamin B₁₂ is present in many forms and contains the mineral cobalt. The compounds with vitamin B₁₂ activity are collectively called “cobalamins”. Vitamin B12 or cobalamin, encompasses a number of forms comprising cyano-, methyl-, deoxyadenosyl- and hydroxy-cobalamin. The cyanocobalamin form is used in supplements and is found in trace amounts in food (1).

Deficiency of vitamin B₁₂ is caused more because of malabsorption of vitamin B12 rather than lack of dietary vitamin B12. Consuming inadequate dietary vitamin B12 is however common in the elderly, vegans or lacto-ovo vegetarians with poor diets.

How much vitamin B12 do we need?

The recommended dietary allowance (RDA) of B12 for adults is 2.4 micrograms. The recommendation increases for women to 2.6 micrograms during pregnancy and 2.8 micrograms during lactation.

How is vitamin B12 absorbed?

In food vitamin B12 is bound to protein, hydrochloric acid released by the stomach is needed to break the bond. The free vitamin B12 can now interact with R proteins released by stomach cells. Once in the intestine cobalamin is released from R proteins and it binds to intrinsic factor to facilitate its absorption in the intestine (1).

Conditions in which vitamin B12 deficiency may occur

Are you a vegetarian?

If you are a strict vegetarian then you might be at a risk of being vitamin B12 deficient compared to non-vegetarians and lacto-ovo-vegetarians. The only sources of vitamin B12 are animal foods. Plant foods do not have any B12. Therefore, eating only foods from plant sources and without taking any vitamin B12 supplements will most likely lead to its deficiency (2).

Surgery of the stomach

The absorption of vitamin B12 depends on R proteins and intrinsic factor secreted by the stomach. These proteins need to interact with vitamin B12 so that the stomach and small intestine can absorb it. If for some reason these proteins are not secreted the absorption of vitamin B12 is affected.

For example, deficiency may occur in case of surgery of the stomach where part of it is removed or stapled.  There would be decrease in the cells that produce R proteins and intrinsic factor which in turn leads to reduction in the absorption of vitamin B12. In people with pernicious anaemia also synthesis of intrinsic factor is reduced thereby lowering vitamin B12 absorption.

Older people

Older people because of gastritis atrophy are at an increased risk of a vitamin B12 deficiency. Their stomachs lose the ability to make hydrochloric acid as they get older. Stomach acid is essential to free the vitamin B12 in food as it is bound to protein so that it interacts with R proteins and intrinsic factor and finally gets absorbed.

Because of the decrease in the amount of hydrochloric acid in the system it might lead to increase in the growth of normal intestinal microflora which probably consume vitamin B12. This situation leads to further reducing the amount of vitamin B12 available to the body for absorption (3).

Gastrointestinal disorders

People with stomach and small intestine disorders like celiac disease and Crohn’s disease may be unable to absorb enough vitamin B12 from food.

Though it is very important that pregnant women and elderly people get adequate vitamin B12, it is necessary for all throughout life to lead an optimal healthy life.


  1. O’Leary, F. and Samman, S. (2010) Vitamin B12 in health and disease, Nutrients. Vol. 2(3). https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3257642/
  1. Wildman, R. (2009) The Nutritionist-Food, Nutrition, and Optimal Health, Vitamins Are Vital Molecules in Food, 197. Routledge, Taylor and Francis Group. Second Edition. New York and London.
  2. Vitamin B12 Fact Sheet for Health Professionals. https://ods.od.nih.gov/factsheets/Vitamin B12 -Health Professional/

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