Vitamin B12 deficiency may have a large variety of causes. In the intricate B12 absorption process a lot can go wrong. All causes listed below can lead to low B12 blood levels and have been described in specialist literature:

Gastric malabsorption

  • pernicious anaemia
  • (partial or total) gastrectomie, Gastric Bypass, Sleeve etc. 
  • Zollinger-Ellison syndrome

Intestinal malabsorption

  • Ileocecal resection or disease, e.g. Crohn inflammatory bowel disease and tuberculosis ileitis
  • Coeliac disease
  • Blind loop syndrome
  • luminal diseases: chronic pancreatitis and gastrinoma
  • parasites: Giardia, bacterial overgrowth and fish tapeworm

Pancreatic Insufficiency 

Reduced intake

  • malnourishment
  • strictly vegan or vegetarian diet

Congenital or hereditary factors

  • intrinsic factor receptor deficiency
  • Imerslund-Gräsback syndrome
  • congenital intrinsic factor deficiency: ‘juvenile’ pernicious anaemia
  • Cobalamin mutation (C-G-1-gen)
  • transcobalamine 2 deficiency

Increased consumption

  • hemolysis 
  • HIV
  • Waldenström’s disease
  • Kahler’s disease

Drugs and medication

  • alcohol
  • laughing gas
  • proton pump inhibitors (antacids)
  • H2 receptor antagonists
  • metformin
  • colchicine
  • Slow K (potassium chloride) preparations
  • cholestyramine
  • birth control pill
  • Levodopa
  • Nitrofurantoine: Be careful with neurological conditions. These antibiotics are frequently prescribed for cystitis and affect vitamin B-intake. See:…/nitrofurantoine… 

    Sources: (a.o.) Hunt, A., Harrington, D., & Robinson, S. (2014). Vitamin B12 deficiency, Clinical review. 349. doi:10.1136/bmj.g5226

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