• Decreased stomach acid
  • Atrophic gastritis
  • Autoimmune pernicious anemia
  • Helicobacter pylori
  • Gastrectomy, intestinal resection
  • Gastric bypass surgery
  • Malabsorption syndromes
  • Crohn’s disease
  • Celiac disease (gluten enteropathy)
  • Chronic pancreatitis
  • Bacterial overgrowth (small bowel)
  • Fish tapeworm
  • Alcoholism
  • Malnutrition—Eating disorders
  • Vegetarianism
  • Advanced liver disease
  • Transcobalamin II deficiency
  • Inborn errors of B12 metabolism
  • Certain drugs
  • Nitrous oxide