Vitamin B12 Deficiency

Causes

• Omeprazole, metformin, antihistamines

• Chronic alcoholism

• Atrophic gastritis

• Pernicious anaemia

• Helicobacter pylori infection (especially in refugee populations)

• Strict vegan diet

• Coeliac disease

• Crohn’s disease

• Bariatric surgery

Note: Long-term metformin use (>4 years) is associated with up to a 20% risk of B12 deficiency due to altered absorption

Supplementation

• Initial Therapy:

  • Hydroxocobalamin 1000 micrograms IM on alternate days for 2 weeks if severe anaemia or neurological symptoms

• Maintenance Therapy:

  • Hydroxocobalamin 1000 micrograms IM every 2–3 months

  • Alternative: Cyanocobalamin 500–1000 micrograms sublingual daily, or oral 50–200 micrograms daily (if no significant malabsorption)

• Monitoring:

  • Recheck B12 levels 3–6 months after commencing supplementation

• Other Options:

  • Intranasal cyanocobalamin 500 micrograms once weekly can be considered for maintenance in patients without severe deficiency but with chronic absorption issues

Key Notes

• Early intervention is crucial to prevent irreversible neuropathy

• Pure dietary deficiency is uncommon unless strict vegan

• Monitor iron and potassium levels after B12 replacement (haematopoietic changes can affect these levels)

• Pernicious anaemia increases gastric cancer risk, may need long-term follow-up