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.