What is vitamin B12?

Vitamin B12 (cobalamin) is a vitamin that plays a crucial role in the synthesis of our genes (DNA and RNA).  Vitamin B12 is very important for our body’s cells to function normally, particularly for red blood cell formation and for neurons (the cells in our nervous system).  

Vitamin B12 deficiency can cause serious health problems:

Vitamin B12 is needed to make new red blood cells and for our nervous system to function properly.   

Vitamin B12 deficiency can lead to medical problems, most notably:

  • Anemia – low red blood cell count or low hemoglobin
  • Some types of dementia 
  • Worsened memory and cognitive function
  • Neuropathy – numbness, weakness, difficulty walking

How can I make sure I’m getting enough vitamin B12?

Vitamin B12 is found mainly in our diets.  Animal products including meat, dairy, and eggs are high in vitamin B12.  Clams and liver have particularly high concentrations of vitamin B12. 

Vitamin B12 is generally not found in plant-based foods.  Vegans and vegetarians need to find other sources of B12 aside from meats.  Many breakfast cereals are fortified with vitamin B12.  Nutritional yeast products also contain vitamin B12. Vitamin supplements can also supply vitamin B12.

Medical causes of low vitamin B12:

  • Pernicious anemia: Pernicious anemia is a condition that occurs when a person cannot absorb vitamin B12 from food. The stomach makes an important protein called “intrinsic factor” that our body needs to absorb vitamin B12. In pernicious anemia, the immune system attacks the intrinsic factor protein or the cells in the stomach and as a result vitamin B12 is not absorbed. 
  • Inadequate dietary intake: Vitamin B12 is present in animal-based foods and not plant-based foods.  Vegans, some vegetarians, or those who limit animal protein intake can become low in vitamin B12. 
  • Food cobalamin malabsorption: In this disorder, individuals cannot absorb vitamin B12 that is bound to proteins in their food.  This is the most common in people who don’t have enough acid in their stomachs to break down protein to release nutrients.  This can be caused by medications, bariatric surgery or gastrectomy, H. pylori infection, or disorders affecting the small intestine.  So although they may have good dietary supply through animal products, they are not absorbing vitamin B12 effectively.  Fortunately they can absorb vitamin B12 in a supplement form because it is not bound to protein in food then.  
  • Medications/drugs: Drugs such as proton pump inhibitors, antacids, metformin, and nitrous oxide all may contribute to vitamin B12 deficiency.
  • Genetic disorders: Although rare, some genetic disorders may play a role.  

How do I make sure I’m getting enough vitamin B12?

The National Institutes of Health (NIH) recommends a daily intake of vitamin B12 of 2.4 mcg per day in adults.  This amount should be slightly increased in those who are pregnant or breastfeeding.   

Generally speaking, diets with adequate animal protein intake have more than sufficient vitamin B12. Fish, poultry, eggs, and red meat are sources that are high in vitamin B12. 

But some people chose not to eat meat for medical or ethical reasons.  In these cases, supplementing with vitamin B12 or choose a food that is fortified with vitamin B12 is a good alternate way to make sure you are getting enough.   There are many breakfast cereals that are fortified with vitamin B12.

How can I supplement vitamin B12?

There are many formulations of vitamin B12 available at the pharmacy.  These include oral tabs, liquids, injectable and sublingual (under the tongue) forms.  All are effective in providing vitamin B12.  Most multivitamins also contain vitamin B12. 

Other names vitamin B12 may be displayed under including cyanocobalamin or methylcobalamin.

References

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Anthony CA. Megaloblastic anemias. In: Hematology: Basic Principles and Practice, 2nd ed, Hoffman R, Benz EJ, Shattil SJ, et al. (Eds), Churchill Livingston, New York 1995. p.552.

Scott JM. Folate and vitamin B12. Proc Nutr Soc 1999; 58:441.

Tefferi A, Pruthi RK. The biochemical basis of cobalamin deficiency. Mayo Clin Proc 1994; 69:181.

Allen RH, Stabler SP, Savage DG, Lindenbaum J. Metabolic abnormalities in cobalamin (vitamin B12) and folate deficiency. FASEB J 1993; 7:1344.

Friso S, Udali S, De Santis D, Choi SW. One-carbon metabolism and epigenetics. Mol Aspects Med 2017; 54:28.

Pruthi RK, Tefferi A. Pernicious anemia revisited. Mayo Clin Proc 1994; 69:144.

Koury MJ, Horne DW. Apoptosis mediates and thymidine prevents erythroblast destruction in folate deficiency anemia. Proc Natl Acad Sci U S A 1994; 91:4067.

Wickramasinghe SN. Morphology, biology and biochemistry of cobalamin- and folate-deficient bone marrow cells. Baillieres Clin Haematol 1995; 8:441.

Ingram CF, Davidoff AN, Marais E, et al. Evaluation of DNA analysis for evidence of apoptosis in megaloblastic anaemia. Br J Haematol 1997; 96:576.

 https://ods.od.nih.gov/factsheets/VitaminB12-HealthProfessional/ (Accessed on May 18, 2017).

 Allen LH. Vitamin B12 metabolism and status during pregnancy, lactation and infancy. Adv Exp Med Biol 1994; 352:173.

Balcı YI, Ergin A, Karabulut A, et al. Serum vitamin B12 and folate concentrations and the effect of the Mediterranean diet on vulnerable populations. Pediatr Hematol Oncol 2014; 31:62.


 

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