What Does Vitamin B12 Do?

What does vitamin b12 do? Signs of Vitamin b12 deficiency can include headache, migraines, numbness, tingling and memory loss. Vitamin B12 (or cobalamin) is responsible for maintaining overall nerve health in the body. Specifically, it helps maintain the myelin sheath which is a substance that coats all nerves.

This includes not only the nerves in the spinal cord and all the nerves in the brain, but also all the nerves running throughout the body.

This is one of the water soluble vitamins that is present in foods and in some medications. What that means is that it does not deposit in the fatty tissues of the body such as the liver. As a result, taking a little more than necessary should not hurt you or cause any problems.

So once again: what does Vitamin B12 do? It is needed for the formation of healthy red blood cells in addition to forming DNA which is the genetic structure inside all cells. Through a complex biochemical reaction, it helps to form DNA and RNA.

Vitamin B12 Absorption

When in foods, it is bound to a protein that is cleaved by the acid in the stomach. If taken in supplementation, it is already in free form and this step is not needed. When absorbed properly from oral form, it binds to a protein produced in the lining of the gut called "intrinsic factor", carried across the gut wall and then can be used in the body. Lack of instrinsic factor is thought to be one of the most common causes of vitamin B12 deficiency symptoms by causing decreased Vitamin b12 absorption.

Pernicious anemia is one of the causes of B12 deficiency. This is an autoimmune disease that affects the lining of the stomach and results in atrophy or shrinkage of the lining. As a result, intrinsic factor cannot be produced leading to B12 malabsorption. Eventually, if the anemia is not treated, B12 deficiency results. This happens even if you are taking adequate amounts of this supplement through food or pills as you simply can't absorb it.

One way to increase absorption is to try sublingual vitamin B12 which is absorbed under the tongue, not through the GI tract.

vitamin b12 deficiency symptoms


Testing is quite easy. It involves a blood test for serum or plasma levels. Other tests that should be ordered include methymelonic acid and homocysteine levels. Both are involved with B12 in body metabolism. Methymelonic acid is the more specific of the two and may start to elevate abnormally up to a year before B12 begins to decline. B12 is stored in the liver and can take up to 2 years to deplete.

Normal plasma levels of B12 are 200-1000 picomol/L but many people will start having symptoms below 350. Generally speaking we start treatment if levels drop below 350. Since oral malabsorption is one of the main causes, B12 injections are the best way to start supplementation. Once someone has been on injections once a month for a year, then a blood level is redrawn to make sure they are at appropriate levels.

Testing for intrinsic factor is very expensive and generally not done unless a physician needs to prove pernicious anemia.

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1. Combs G. Vitamin B12 in The Vitamins. New York: Academic Press, Inc., 1992.
2. Zittoun J, Zittoun R. Modern clinical testing strategies in cobalamin and folate deficiency. Sem Hematol 1999;36:35-46. [PubMed abstract]
3. Institute of Medicine. Food and Nutrition Board. Dietary Reference Intakes: Thiamin, Riboflavin, Niacin, Vitamin B6, Folate, Vitamin B12, Pantothenic Acid, Biotin, and Choline. Washington, DC: National Academy Press, 1998.
4. Clarke R. B-vitamins and prevention of dementia. Proc Nutr Soc 2008;67:75-81. [PubMed abstract]


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