Vitamin B12 (Cobalamin) Deficiency

Vitamin B12 (cobalamin) is a coenzyme required for various metabolic functions in the body, including fat metabolism, carbohydrate metabolism, and protein synthesis. It plays an additional critical roles in hematopoiesis and a major role synthesizing and maintaining myelin in the central and peripheral nervous system.

Vitamin B12 deficiency is an important cause of reversible neuropsychiatric symptoms and often overlooked.[1][2][3] Many case reports and series have reported psychosis,[4] hallucinations,[5][6] mood, irritability, dementia, catatonia,[7] delirium, hallucinations, and other neuropsychiatric symptoms in B12 deficiency.[8][9] The specific association between the role of B12 deficiency and neuropsychiatric symptoms is not well understood due to the lack of studies.

A Quick Review on Vitamins

Vitamins are either water-soluble (vitamins B and C), or fat-soluble (vitamins A, D, E, K)
  • Fat-soluble vitamins are dependent on absorption from the ileum and pancreas. Toxicity is easier with fat soluble vitamins because these vitamins accumulate in fat. Malabsorption syndromes such as cystic fibrosis and/or celiac disease) can result in fat-soluble vitamin deficiencies.
  • Water-soluble vitamins are usually important coenzymes in cellular processes or precursors to coenzymes. All are excreted easily from the body, except for vitamins B12 and B9. B vitamin deficiency can result in glossitis, dermatitis, and diarrhea. For certain vitamin B deficiencies (B1 and B12), there can be neuropsychiatric and cognitive symptoms as well. Broadly, the B vitamins include:

Very large reserve pools of B12 are stored primarily in the liver and can last for several years. Causes of B12 deficiency include:

  • Dietary insufficiency
    • B12 can be low in vegetarians or vegans, or in the elderly when there is malnutrition. This is because B12 is generally only found in meat and dairy products.
  • Decreased absorption
    • Deficiency of intrinsic factor (IF), leading to pernicious anemia
    • GI dysfunction such as hypochlorhydria
    • Long-term use of proton pump inhibitors
  • Inadequate utilization
    • Vitamin B12 is binds to the transport protein, transcobalamin II. In individuals with a transcobalamin II deficiency, this process is disrupted, and B12 cannot be delivered to sites of utilization and storage.
    • Nitrous oxide is a commonly abused inhalant drug and can precipitate vitamin B12 deficiency when used chronically and acutely, especially in individuals with pre-existing low vitamin B12 reserve.[10][11]
  • Complete blood count will show macrocytic, megaloblastic anemia, with hypersegmented polymorphonuclear leukocytes
  • Serum B12 level should be ordered first, if B12 levels are borderline low, then you should also order:
    • Serum methylmalonic acid (normal level, <400), elevated level of methylmalonic acid is more sensitive and specific for the diagnosis of B12 deficiency
    • Serum homocysteine (normal level, <14)
  • Note that if someone is taking vitamin B9 (folate) supplementation, this can mask the hematologic symptoms of B12 deficiency, but not the neurologic symptoms.

Although laboratory norms and ranges may show that a serum vitamin B12 level between 200 pg/mL and 900 pg/mL is considered normal, a minimum level of 300 to 350 pg/mL is desirable in the elderly.[12]

On exam, patients may have paresthesias.

If an individual is hospitalized, unable to take medications by mouth, or have severe neurological/psychiatric symptoms, then intramuscular (IM) administration of synthetic B12 (cyanocobalamin) is the treatment of choice. Otherwise, oral intake should be encouraged.[13]

Vitamin B12 Dosing

Oral • Cyancobalamin 1000mcg PO daily
• Ranges from 300 to 2000mcg have been commonly used with no evidence of toxicity
IM • Cyancobalamin 100 mcg for 5 to 10 days to saturate B12 stores
• Then 100 to 200 mcg qmonthly until normalization of the hemoglobin and hematocrit
• Then 100 mcg monthly to maintain remission