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What are the causes?

There are many causes for B12 deficiency. Autoimmune pernicious anaemia is just one. However having one autoimmune condition can unfortunately predispose some to develop others. For example many people who are coeliac or have thyroid dysfunction are also B12 deficient. Many common drugs can cause B12 deficiency as can some surgery and parasites, please see below.

(Please note that folate deficiency which often accompanies B12 deficiency, can be caused by many commonly prescribed drugs too).

We have developed an app to help determine your risk of B12 deficiency.

The What to do Next page is a good place to start if you think you may be deficient.  If you need personalised help please see the contact page for more information.

You can view a 90 minute broadcast on B12 deficiency with me, from the Academy of Physical Medicine here. There is a small charge. See a clip here


 The six most commonly identified causes of B12 deficiency are;

• An inability to absorb B12 

• A diet deficient in B12

• An autoimmune disorder

• A genetic defect (including MTHFR, MTRR)

• Medications that hinder the body's ability to use B12

• A secondary deficiency in a child, stemming from maternal deficiency prior to conception, during pregnancy or during nursing.

Toxic exposure could also be a factor please also see the Antidote page

More below;

  • Decreased stomach acid
  • Atrophic gastritis
  • Autoimmune pernicious anaemia
  • Helicobacter pylori
  • Gastrectomy, partial or complete
  • Gastric bypass surgery (weight loss)
  • Intestinal resection
  • Partial or complete ileectomy
  • Gastrointestinal neoplasms
  • Malnutrition
  • Eating disorders  - anorexia - bulimia
  • Inadequate diet
  • Vegetarianism / veganism
  • Malabsorption syndromes
  • Alcoholism
  • Crohn’s disease
  • Coeliac disease (gluten enteropathy)
  • Diphyllobothrium infection
  • blind loop syndrome
  • diverticulosis
  • inflammatory bowel disease
  • small bowel overgrowth (SIBO)
  • tropical sprue
  • gastric irradiation
  • illeal irradiation (bladder, cervix, uterus, prostate)
  • Inborn errors of B12 metabolism
  • Transcobalamin II deficiency
  • Pancreatic exocrine insufficiency & Chronic pancreatitis
  • Imerslund Gräesbeck syndrome
  • Zollinger - Ellison Syndrome
  • Bacterial overgrowth (small bowel)
  • Fish tapeworm
  • Advanced liver disease

Drug induced causes - Please note; this list is not exhaustive

  • Antacids
  • Colchicine (treatment of gout)
  • H2 Blockers (Zantac, Tagamet, Pepcid)
  • Metformin - Diabetes drug (Glucophage)
  • PPI's - Proton pump inhibitors (Omeprazole, Nexium, Prevacid, Protonix)
  • Nitrous oxide anaesthesia
  • Nitrous oxide recreational abuse (Laughing gas / Whippets / Hippy crack)
  • Levodopa (treatment of Parkinson's)
  • Mycifradin sulphate (Neomycin) antibiotic
  • Para aminosalicylates  antibiotic
  • Phenytoin (Dilantin) - anti-epileptic
  • Potassium chloride (K-Dur)
  • Cholestyramine (Questran)
  • Chemotherapy and radiation treatment

Increased demands

  • Chronic Hemoltic anaemia
  • Hyperthyroidism
  • Multiple myeloma
  • Myeloproliferative disorders
  • Neoplasms
  • Pregnancy

Information provided with kind permission of Sally M. Pacholok R.N. & Dr. Jeffrey J. Stuart.

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