Neurological Disorders: B12-Deficiency


Vitamin B12-deficiency, especially occurring for a prolonged period is a serious health concern, and can cause myriad neurological disorders. A Neurologist is frequently involved in the care of these patients.

This vitamin, also known as cobalamin, participates in several prime metabolic activities in the body, and it is lumped under the group of “water soluble vitamins”.

It is an essential vitamin; this means we human beings cannot synthesize it in our body, rather it needs to be supplied through food (or pharmaceutical sources). Unfortunately the plant sources of food are deficient in this vitamin; however the animal products like liver & meat are rich with it.

It also means the strict vegetarians (vegans, are one of the susceptible groups for this vitamin deficiency.

Anyway the good news is human body needs only very tiny amount of this vitamin for its daily requirements, which is around 2.5 micrograms for a typical adult. Human body stores between about 2 and 5 mg of B12, so generally only a prolonged decreased intake will manifest with diseases.

More details on B12

This vitamin occurs in many different forms, and they all contain the rare element cobalt, and all of these forms possess vitamin activity.

Cobalmin & hydroxyl-cobalamin are the two natural forms and the synthetic form is cyanocobalamin and is generally used as the dietary supplement or pills. Methyl and adenosyl forms are the active forms and they are used during the metabolic functions inside the cells. Methylcobalamin is too available in the market recently.

The orally consumed B12 will be destroyed by the gastric acid, and this is prevented by its combining to a glycoprotein (a complex of sugar and protein molecules). As this compound reaches duodenum, the first part of small intestine, the enzymes secreted by pancreas liberate cobalamin from this complex, and the free vitamin associates with another glycoprotein called IF (intrinsic factor) and then reaches ileum (distal small intestine) where finally it gets absorbed.

What causes B12 deficiency?

• Vegan (strict vegetarian diet)
• After stomach surgery
• After intestinal surgery
• Pernicious anemia (autoimmune disorder)
• Intestinal parasites like fish tapeworm
• Medication side effect example - metformin

How does patient manifest?

B12-deficiency may manifest as;

• Cognitive dysfunctions not amounting to dementia
• Frank dementia
• Neuropsychiatric manifestations
• Spinal cord damage (subacute combined degeneration)
• Neuropathy conditions (nerve damage)
• Anemia etc

Many cognitive & neuropsychiatric manifestations (confusion, memory deficits, delusions, hallucinations, psychosis etc) have been ascribed to B12-deficiency. Neuropathy can cause numb feeling, tingling (pins & needle) sensation, weakness in the limbs, gait unsteadiness etc. A form of spinal cord damage called as subacute combined degeneration can produce unsteadiness of gait, muscle weakness, sensory complaints, bowel, and bladder symptoms.


B12-deficiency has to be confirmed by laboratory tests.

Blood level of this vitamin is the mot frequently employed test. If the blood range is borderline then additional tests like serum methylmalonoic acid and homocystine (sometimes done on urine too) are of immense help.

Blood cell counts & hemoglobin estimation, peripheral smear and sometimes a bone marrow biopsy may be necessary.

If pernicious anemia is suspected tests like antiparietal cell antibodies, intrinsic factor antibodies, gastric mucosa biopsy etc may be necessary. Schilling test, once popular, is now-a-days rarely employed.


If a reversible cause is suspected e.g. drug or intestinal parasite causing the deficiency then it is appropriately managed.

B12 supplementation is must once the deficiency of this vitamin is suspected irrespective of what is causing the deficiency. Lifelong therapy is needed if the cause for this vitamin’s deficiency is irreversible e.g. pernicious anemia.

Depending upon the severity of deficiency and the organ or tissue damage it is administered either orally or parenterally (by injection) route. Injection route is more reliable and is the traditional route of administration of this vitamin; however some authorities believe that high oral doses are ok too.

B12-Deficiency to Neurology Articles