B12 Deficiency

by Dr. Thomas Lundberg, MD 25. July 2014 09:56

I am particularly vigilant for signs of B12 deficiency in my patients, as it is a reversible cause of dementia (if you are older than 50 I probably have you’re attention now).  Our diet is replete with B12 so deficiency is almost always due to poor absorption of B12.  There are a few caveats to B12 deficiency that are important to know.

  1. The normal range of B12 reported by most labs is 200-1100.  However, approximately 3-4% of patients with a B12 level 200-400 are “functionally deficient.”  The long story short is that you want you B12 level greater than 400.
  2. The reversibility of dementia due to B12 deficiency is time dependent i.e. the longer one is deficient the greater the chances of permanent damage.  As such early detection is key. 
  3. Metformin, the most commonly prescribed oral medicine for diabetes, is associated with low B12 levels.  I periodically check a B12 level on my diabetics on Metformin.  It is my experience that B12 deficiency is common in diabetics on long term Metformin.
  4. A very early and subtle clue to possible B12 deficiency can be found on the complete blood cell count.  If the “RDW” is elevated B12 deficiency is a possibility.  Although your physician should automatically check this, request it if not done so.
  5. Although poor absorption of B12 leads to B12 deficiency, most patients B12 levels can be raised with 500-1000 mcg of B12 supplement a day.  Some patients are not able to absorb any B12, and are therefore dependent on monthly intramuscular B12 shots. 




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