What is the recommended oral vitamin B12 (cobalamin) supplementation dose?

Oral Vitamin B12 Supplementation Dose

For general supplementation in healthy adults, take 2.4 micrograms daily; for treatment of deficiency or malabsorption, take 1000-2000 micrograms (1-2 mg) daily orally. 1

Maintenance/Prophylactic Dosing

• Healthy adults: 2.4 micrograms per day is the WHO-recommended dose for routine supplementation 1
• Adults over 50 years: Should use crystalline vitamin B12 (fortified foods or supplements) rather than dietary sources alone, as atrophic gastritis impairs absorption of protein-bound B12 2, 3
• Post-bariatric surgery patients: 1000 micrograms daily orally OR 1000 micrograms intramuscularly every 3 months 1, 4
  • After Roux-en-Y gastric bypass or biliopancreatic diversion: 1000-2000 mcg/day sublingual OR 1000 mcg/month IM 4
  • After sleeve gastrectomy or gastric banding: 250-350 mcg/day oral or 1000 mcg/week sublingual 4

Treatment of Deficiency

For confirmed vitamin B12 deficiency, oral high-dose therapy (1000-2000 micrograms daily) is equally effective as intramuscular injections for correcting anemia and neurologic symptoms in most patients. 2, 3

Oral Treatment Protocol

• Standard deficiency without neurological symptoms: 1000-2000 micrograms daily orally 1, 5, 2
• Minimum effective dose: Studies show 647-1032 micrograms daily is the threshold for efficacy 5
• Optimal dose: 1000 micrograms daily is recommended as it reliably reverses biochemical deficiency 5, 2
• Duration: Continue until deficiency is corrected, or indefinitely if the underlying cause cannot be reversed 4

When Intramuscular Therapy is Preferred

Intramuscular administration should be used in specific circumstances despite oral therapy being generally effective 2:

• Severe neurological involvement: 1000 micrograms IM on alternate days until no further improvement, then 1000 micrograms every 2 months 1, 4
• Without neurological involvement: 1000 micrograms IM three times weekly for 2 weeks, then 1000 micrograms every 2-3 months lifelong 1, 4
• Compliance concerns: Patients unable to adhere to daily oral dosing 5
• Swallowing difficulties: Patients who cannot take oral medications 5
• Severe clinical symptoms: Rapid correction needed 5, 2

Special Population Considerations

• Vegans/strict vegetarians: Should consume fortified foods or take supplements containing crystalline B12 2, 3
• Metformin users (>4 months): Consider screening and supplementation 2
• Proton pump inhibitor/H2 blocker users (>12 months): Consider screening and supplementation 2
• Ileal resection (>20 cm): 1000 micrograms monthly IM for life 1, 4
• Pregnant women post-bariatric surgery: Continue 1000 micrograms every 3 months IM or 1000 micrograms daily orally, with B12 levels checked every 3 months 1, 4

Monitoring and Follow-up

• During treatment: Check serum B12 and homocysteine every 3 months until stabilization 4, 6
• After stabilization: Monitor once yearly 4
• Target homocysteine: <10 μmol/L for optimal results 4, 6
• Symptom assessment: Evaluate for resolution of fatigue, neurological symptoms, and hematological abnormalities 6

Critical Precautions

• Never give folic acid before treating B12 deficiency, as it can mask B12 deficiency and precipitate subacute combined degeneration of the spinal cord 4, 6
• Do not discontinue supplementation even if levels normalize in patients with ongoing risk factors (malabsorption, bariatric surgery, strict vegetarian diet), as lifelong therapy is typically required 4, 6
• Oral doses ≤15 micrograms daily are inadequate for patients with malabsorption, particularly post-bariatric surgery 7

Formulation Considerations

• Crystalline B12 (cyanocobalamin, methylcobalamin, hydroxocobalamin) is better absorbed than naturally occurring dietary B12 2, 3
• Methylcobalamin or hydroxocobalamin may be preferable to cyanocobalamin in patients with renal dysfunction 1, 4
• FDA-approved dosing for over-the-counter cyanocobalamin is 1000 mcg (1 tablet) daily, preferably with a meal 8