Vitamin B12 is a vital component of myelin production in the nervous system. Mild deficiency can lead to neuropathy, whilst extremely severe deficiency can result in irreversible neurological complications such as subacute combined degeneration of the spinal cord. Vitamin B12 can demonstrate a macrocytic anaemia on blood film.
Causes of Deficiency:
Pernicious Anaemia – this is the most common cause of vitamin B12 deficiency. It is an autoimmune disease most commonly occurring in the 45 – 65 year old age group and predominantly in females. It involves gastritis, atrophic changes and loss of normal gastric glands, mucosal architecture, parietal and chief cells, resulting in the absence of gastric acid. This results in a lack of intrinsic factor production needed to bind to vitamin B12 to aid absorption.
- Inadequate intake: strict vegans as no animal sources in their diet
- Malabsorption states ileal resection, intestinal inflammation e.g. Crohn’s Disease
- Post gastrectomy as fewer parietal cells remain to produce intrinsic factor
- Bacterial overgrowth as a result of blind loop syndrome
- Malignant disease requiring radiotherapy causing irradiation of the terminal ileum
- Gut infection (tapeworm)
- Medications – colchicine, neomycin, metformin, anticonvulsants
- Long-term use of PPIs or H2 receptor antagonists which lower available gastric acid
