As we were looking to the symptoms of vitamin B12 deficiency in last weeks Health post, this week we focus on the cause of vitamin B12 deficiency.

A common problem, vitamin B12 deficiency affects the general population, especially the elderly. There are two types of sufferers from vitamin B12 deficiency. The first group is comprised of asymptomatic vitamin B12 deficiency and the other one is composed of hematologic vitamin B12 deficiency.


Vitamin B12 is a required nutrient and lack or deficiency of this vitamin may lead to serious impairment of normal bodily functions. Vitamin B12 is primarily obtained from animal proteins like red meat, poultry, fish, eggs, and dairy. Plants and vegetables do not contain vitamin B12, unless they have been contaminated by soil microorganisms, so plants and vegetables are not considered as consistent sources of the vitamin. Ovolactovegetarians and lactovegetarians can get adequate cobalamin, or vitamin B12, but strict vegetarians or vegans risk deficiency.


The body’s method of absorbing vitamin B12 from foods is complex. And that is why a defect in the absorption process can become a cause of vitamin B12 deficiency. Often, the absorption of vitamin B12 occurs in the stomach where the release gastric acid and pepsin help release cobalamin from animal proteins. Vitamin B12 absorption may also occur in the mouth where it binds preferentially to salivary R protein.

Pancreatic enzymes and an alkaline pH may also react with vitamin B12 and contribute to its rate of absorption. These two compounds digest the R protein-cobalamin complex but before it is absorbed, vitamin B12 first binds to intrinsic factor (IF) to form an IF-cobalamin complex.

Conditions that Affect Absorption

One cause of vitamin B12 deficiency is certain medical conditions that affect vitamin B12 absorption. These conditions include low consumption of vitamin B12 because of eating foods that lack vitamin B12. The cause of this vitamin B12 deficiency is veganism, or those strict vegetarians that eat only plants and vegetables that do not contain any cobalamin.

The failure to digest food protein is also a leading cause of vitamin B12 deficiency. This may be caused by the decreased release of gastric acid, which is in turn caused by an underlying health condition.

As briefly mentioned earlier, absorption of vitamin B12 by the body is accomplished when all the factors ?that is, the compounds necessary are present. Vitamin B12 combined with salivary R protein need to bind with intrinsic factors in the small intestine in order for the vitamin to be properly absorbed. If there are no intrinsic factors, then absorption fails and thus, this shortage of a vital compound can be a cause of vitamin B12 deficiency. Conditions that lead to absence of intrinsic factor include pernicious anemia and gastrectomy.

Image courtesy of Simon Howden /

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