Vitamin B12 deficiency Flashcards
What synthesises B12?
Microorganisms
What sources contains B12?
Meat, fish, dairy products
What is the recommended daily allowance of B12?
1.25 mcg
What is the western daily consumption of B12?
5-30 mg
What is the estimated daily loss of B12?
1-3 mcg
How long will B12 store if supply cut off?
2-5 years
Explain passive absorption of B12
Through buccal, duodenal, ileal mucosa
Rapid but inefficient
<1% of oral dose absorbed
Explain active transport of B12
Normal physiological mechanism
Occurs through ileum
Mediated by gastric intrinsic factor
~70% of ingested amount is absorbed
Where is intrinsic factor produced?
Parietal cells and secretion parallels that of acid
What happens in the absence of intrinsic factors?
Inadequate amount of B12 absorbed
Causes megaloblastic anaemia called pernicious anaemia
What is pernicious anaemia?
Autoimmune atrophic gastritis
Destruction of gastric parietal cells and the associated lack of intrinsic factor
Immune response is directed against H+/K+ ATPase
Also causes achlorhydria (production of gastric acid is low or absent)
Can also be caused by antibodies directed against intrinsic factor
What are the causes of B12 deficiencies?
Inadequate dietary intakes
Loss of intrinsic factor
Abnormally functioning intrinsic factor
What drugs induce B12 deficiency?
PPIs, oral contraceptive, hormonal therapy, metformin, cholchicine
What is the normal serum concentration of B12?
115- 1000 pmol/L
What is the hallmark of symptomatic B12 deficiency?
Megaloblastic anaemia
