Vitamin B12 Supplementation Recommendations
For vitamin B12 deficiency, the recommended approach is oral supplementation of 1000 micrograms daily for most patients, with intramuscular injections (1000 micrograms every 2-3 months) reserved for those with severe malabsorption issues or neurological symptoms. 1, 2
General Dosing Guidelines
- The standard recommended daily dose for healthy adults is 2.4 micrograms per day 1
- For treatment of deficiency, higher doses of 1000-2000 micrograms (1-2 mg) daily are recommended 1, 3
- Oral administration of high-dose vitamin B12 (1000-2000 micrograms daily) is as effective as intramuscular administration for most patients with deficiency 3, 4
- High-dose oral supplementation works through passive diffusion, bypassing the need for intrinsic factor 5, 4
Route of Administration
Oral Supplementation
- Oral supplementation with 1000 micrograms daily has been shown to effectively treat vitamin B12 deficiency, even in patients with pernicious anemia 4, 3
- Oral route is comparable to intramuscular route for correcting vitamin B12 deficiency in most cases 6, 3
- Approximately 1% of oral vitamin B12 is absorbed through simple diffusion, which is adequate with high doses 5
Intramuscular Supplementation
- Recommended for patients with severe deficiency, neurological symptoms, or significant malabsorption issues 2, 3
- Initial treatment protocol for severe deficiency: 1000 micrograms intramuscularly three times a week for 2 weeks 2
- For neurological involvement: 1000 micrograms intramuscularly on alternate days until symptoms improve 2
- Maintenance treatment: 1000 micrograms intramuscularly every 2-3 months 2
Special Populations
Post-Bariatric Surgery
- Patients should receive vitamin B12 supplementation at 1 mg every 3 months via intramuscular injection or 1 mg daily orally 7, 1
- Patients with more than 20 cm of distal ileum resected should receive monthly 1000 microgram intramuscular injections 2
Elderly Patients
- Higher risk of B12 deficiency, with metabolic B12 deficiency present in 18.1% of patients over 80 years 7
- Should be screened regularly for deficiency, especially if taking proton pump inhibitors or metformin 3
Pregnant Women
- Recommended daily intake is 4 micrograms during pregnancy 5
- For pregnant women after bariatric surgery, 1 mg every 3 months via intramuscular injection or 1 mg daily orally 7, 1
Vegetarians and Vegans
- Should consume foods fortified with vitamin B12 or take supplements due to absence of B12 in plant foods 5, 3
- Deficiency has been recognized in infants of vegetarian mothers who were breastfed 5
Monitoring
- Serum B12 and total homocysteine should be measured to assess vitamin B12 status 7
- Target homocysteine level should be <10 μmol/L for optimal results 7
- In patients with deficiency, monitoring should occur every 3 months until stabilization, then once a year 7
- For patients after bariatric surgery planning pregnancy, B12 levels should be checked every 3 months 7
Type of Vitamin B12
- Cyanocobalamin is the most widely used form 5
- Methylcobalamin or hydroxocobalamin may be preferable to cyanocobalamin in patients with renal dysfunction 7, 1
- Both methylcobalamin and adenosylcobalamin are essential and have distinct metabolic functions 6
Important Cautions
- Never administer folic acid before treating vitamin B12 deficiency, as it may mask B12 deficiency and precipitate subacute combined degeneration of the spinal cord 2, 5
- Patients with pernicious anemia require lifelong supplementation to prevent irreversible neurological damage 5
- B12 deficiency is commonly missed because serum B12 in the normal range is often accepted as ruling out deficiency 7
Therapeutic Considerations
- Treatment should continue until the reason for deficiency is corrected, or indefinitely if the cause cannot be reversed 7, 5
- For patients with pernicious anemia, supplementation is required for life 5, 4
- Patients who have had bariatric surgery should receive 1 mg of oral vitamin B12 per day indefinitely 3