What is the role and treatment of vitamin B12 deficiency?

Vitamin B12 Deficiency: Role and Treatment

Vitamin B12 deficiency requires prompt treatment with either intramuscular hydroxocobalamin or high-dose oral supplementation, with treatment protocols determined by the presence of neurological symptoms and the underlying cause of deficiency. 1, 2

Diagnosis and Clinical Presentation

• Vitamin B12 deficiency presents with hematological abnormalities (megaloblastic anemia) and/or neurological symptoms including paraesthesia, numbness, muscle weakness, abnormal reflexes, gait ataxia, and myelopathies 3
• Diagnosis should include serum B12 levels and functional biomarkers such as homocysteine and methylmalonic acid, as metabolic B12 deficiency can occur even with normal serum B12 levels 3, 2
• Metabolic B12 deficiency is defined as serum B12 below 258 pmol/L with elevated plasma total homocysteine or methylmalonic acid 3
• Elderly individuals have higher risk of B12 deficiency, with metabolic B12 deficiency present in 18.1% of patients over 80 years 3

Treatment Protocols

Based on Clinical Presentation

• For patients with neurological involvement:

  • Administer hydroxocobalamin 1 mg intramuscularly on alternate days until no further improvement 1, 2
  • Then transition to maintenance with hydroxocobalamin 1 mg intramuscularly every 2 months 1, 2

• For patients without neurological involvement:

  • Initial treatment is hydroxocobalamin 1 mg intramuscularly three times a week for 2 weeks 1, 2
  • Follow with maintenance treatment of 1 mg intramuscularly every 2-3 months lifelong 1, 2

Based on Cause of Deficiency

• Malabsorption (pernicious anemia, ileal resection, bariatric surgery):

  • Parenteral vitamin B12 is required for life 1, 4
  • Patients with more than 20 cm of distal ileum resected should receive prophylactic vitamin B12 injections (1000 μg) monthly for life 1

• Dietary deficiency:

  • High-dose oral vitamin B12 (1-2 mg daily) can be effective in patients without malabsorption issues 5
  • Patients older than 50 years and vegans/vegetarians should consume foods fortified with vitamin B12 or take supplements 5

Special Considerations

• Methylcobalamin or hydroxocobalamin may be preferable to cyanocobalamin in patients with renal dysfunction 3
• Never administer folic acid before treating vitamin B12 deficiency, as it may mask underlying B12 deficiency and precipitate subacute combined degeneration of the spinal cord 1, 2
• B12 deficiency is associated with increased risk of stroke due to hyperhomocysteinemia; supplementation with B vitamins can reduce stroke risk by 43% 3
• Target homocysteine level should be <10 μmol/L for optimal results 3, 1

Monitoring

• Monitor neurological symptoms regularly during treatment, as improvement indicates effective therapy 1
• In patients with deficiency, monitoring should occur every 3 months until stabilization, then once a year 1
• Serum B12 and total homocysteine should be measured to assess vitamin B12 status 3, 1

High-Risk Populations

• Elderly individuals (>80 years): 18.1% have metabolic B12 deficiency 3
• Patients after bariatric surgery require close monitoring and supplementation 1, 5
• Patients with ileal Crohn's disease involving more than 30-60 cm of ileum 1
• Vegans and strict vegetarians 1, 5
• Patients taking metformin for more than four months or proton pump inhibitors/H2 blockers for more than 12 months 5

B12 deficiency is a significant but often overlooked condition with potentially irreversible neurological consequences if left untreated. Early diagnosis and appropriate treatment are essential to prevent permanent neurological damage 3, 2.