November 19, 2012

Causes of Vitamin B12 Deficiency

Reduced dietary intake

Vitamin B12 is present in meat and dairy products and reduced dietary intake occurs mainly in vegans, strict vegetarians and in cases of severe prolonged malnutrition. Perhaps surprisingly, poor dietary intake is generally an uncommon cause of deficiency.

Malabsorption

Vitamin B12 may be malabsorbed as a result of several disorders affecting any part of the digestive system from the stomach to the site of its absorption in the lower small intestine.

Gastric factors

Stomach acid and an enzyme in gastric juice called pepsin are needed to release B12 from food binders.  Diseases affecting this process include non-specific gastritis, gastric surgery, acid suppressing drugs, and alcohol abuse. Intrinsic Factor is also needed to help absorb B12 across the gut, and this can be deficient as a result of an autoimmune disorder, atrophic gastritis or surgical resection, all of which result in defective secretion.

Addison’s anaemia

This usually occurs in those aged 60 and over and is more common in Europeans and especially Scandinavians.  Patients have typical clinical features of B12 deficiency and a macrocytic anaemia.  It is frequently associated with other autoimmune diseases such as thyroiditis.

Pancreatic disease

B12 deficiency can also occur as a result of chronic pancreatitis and cystic fibrosis.

Intestinal factors

There are many other potential causes of B12 malabsorption relating to the intestine. These include surgery (Ileal resection) parasitic infestation, obstructive jaundice, coeliac disease and tropical sprue. There are also several rare genetic causes of a deficiency.

Deficiency or Depletion?

As in other nutrient deficiencies, it is important to remember that deficiency can result from excess requirements; i.e. vitamin B12 depletion.  In later blog updates we will return to this issue in the context of dementia and memory loss.


 

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