Vitamin B12 Supplementation Dosing Guidelines
For vitamin B12 supplementation, the recommended dosing is 1000 μg monthly via intramuscular injection for deficiency treatment, or 250-350 μg daily (or 1000 μg weekly) for oral supplementation to prevent deficiency. 1, 2
Dosing Based on Clinical Scenario
Prevention of Deficiency
- Oral supplementation:
- For high-risk populations (vegans, vegetarians, elderly >75 years):
- Daily B12 supplementation of 250-350 μg 2
Treatment of Deficiency
Mild Deficiency without Malabsorption
- Oral therapy:
Deficiency with Malabsorption Issues
- Intramuscular injection:
Severe Deficiency or Neurological Symptoms
- Intramuscular injection preferred:
Special Populations
Post-Bariatric Surgery
- 1000 μg vitamin B12 monthly intramuscularly after RYGB and BPD 1
- For LSG or LAGB: vitamin B12 supplements as needed to maintain normal levels 1
- 1000 μg oral B12 daily indefinitely for patients who have had bariatric surgery 2, 3
Crohn's Disease with Ileal Involvement
- 1000 μg vitamin B12 monthly if >20 cm of distal ileum is resected 2
Elderly Patients
- Higher prevalence of deficiency (10-15% of people over age 60) 6
- Oral doses of 647-1032 μg daily may be needed to normalize mild deficiency 7
- Consider screening in adults older than 75 years 3
Monitoring Recommendations
- Check B12 levels at 3,6, and 12 months in the first year after starting monthly injections 2
- Follow-up testing within 3 months after starting supplementation to assess response 2
- Annual monitoring once levels have stabilized 2
- Monitor for vitamin B12 deficiency when patients are treated with metformin for more than 4 years 1
Important Considerations
- Untreated vitamin B12 deficiency for more than 3 months may produce permanent degenerative lesions of the spinal cord 2
- Patients with pernicious anemia require monthly injections for life 5
- Folic acid may mask B12 deficiency hematologic manifestations while allowing neurological damage to progress 5
- Patients using metformin, proton pump inhibitors, or H2 blockers for extended periods should be monitored for B12 deficiency 2, 3
Administration of Injections
- Use a 1-inch, 22-25 gauge needle for intramuscular injections 2
- Preferred injection sites: deltoid muscle of the upper arm or anterolateral aspect of the thigh 2
- Inject slowly into the muscle after aspiration to ensure the needle is not in a blood vessel 2
The evidence clearly supports that higher doses of vitamin B12 (1000 μg) are more effective than lower doses for both treatment and maintenance, with no disadvantage in cost or toxicity 4.