Vitamin B12 deficiency historical perspective

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

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Common Causes

Vitamin B 12 deficiency may be caused by:

Decrease intake 

  • Strict vegan diet more than 3 years .
  • Breast fed infants of pure vegan may also develop deficiency .
  • Malnutrition most likely happen in elderly patients.

Malabsorption

  • Decrease intrinsic factor  due autoimmune destruction of parietal cell
  • Decrease Gastric acid production due to proton pump inhibitor and histamine 2 receptor antagonists
  • Gastric by pass surgery because intrinsic factor is produce by parietal cell of stomach 
  • Tapeworm (Diphyllobothrium latum ) ingested from contaminated fish , tapeworm saps nutrients
  • Crohn's disease

Increased requirement

  • pregnancy

Pathophysiology

  • Dietary Vitamin B12 binds to salivary R factor then the complex arrives at small intestine
  • In duodenum Vitamin B12 is detach from R- factor by pancreatic proteases
  • Now free B12 binds to intrinsic factor which is secreted by gastric parietal cell
  • The intrinsic factor - B12 complex is absorbed in the ileum
  • Absorbed vitamin B12 is use in metabolic pathways which is important for neurologic and hematologic function if vitamin B12 is deficit regardless of the cause many impairments may occur
  • Vitamin B12 is a cofactor for the enzyme methionine synthase which convert homocysteine to methionine as a result methyl- THF is converted to THF which is use in synthesis of pyrimidine base of DNA.
  • In B12 deficiency homocystein accumulate which cause megaloblastic anemia and hypersegmented neutrophils.

References

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