Recommended Daily Dosing for Methylcobalamin (Vitamin B12)
The recommended daily dose of methylcobalamin (Vitamin B12) for healthy adults is 2.4 micrograms per day, while higher doses of 1000-2000 micrograms (1-2 mg) daily are recommended for those with deficiency or absorption issues. 1
Standard Dosing for Healthy Adults
- The Dietary Reference Intake (DRI) for healthy adults is 2.4 μg/day based on maintenance of hematological status and serum cobalamin values 2
- The Adequate Intake (AI) estimated by EFSA is slightly higher at 4 μg/day for healthy adults 2
- During pregnancy, the recommended intake increases to 5 μg/day 2
- During lactation, breast-feeding mothers should receive at least 2.8 μg/day of cyanocobalamin orally 2
Therapeutic Dosing for Deficiency
- For vitamin B12 deficiency treatment, much higher doses are required - typically 1000-2000 μg (1-2 mg) daily 1
- For severe deficiency with neurological symptoms: 1000 μg intramuscularly three times a week for 2 weeks, followed by maintenance treatment of 1000 μg every 2-3 months 1
- Oral supplementation studies show that doses of 647-1032 μg daily are needed to achieve 80-90% of maximum reduction in methylmalonic acid (a marker of B12 deficiency) 3
- The lowest effective oral dose for normalizing mild vitamin B12 deficiency is more than 200 times greater than the recommended dietary allowance 3
Dosing for Specific Conditions
For patients with compromised cobalamin absorption (short bowel syndrome, bariatric surgery, Crohn's disease, gastrectomy, atrophic gastritis, ileal resection):
- Daily oral dose of 350 μg methylcobalamin, OR
- IM injections of 1000-2000 μg every 1-3 months 2
For acute clinical symptoms of deficiency or conditions with anti-intrinsic factor antibodies:
- Start with high doses of 1000 μg methylcobalamin IM every second day for 2 weeks (or daily for 5 days)
- Continue at least twice monthly until resolution of clinical signs 2
Administration Routes
- Oral supplementation is effective for most individuals without absorption issues 1
- Intranasal and sublingual administration are alternative routes for those with mild absorption issues 2
- Intramuscular (IM) injection is preferred for those with severe malabsorption or neurological symptoms 2
- For parenteral nutrition, at least 5 μg cyanocobalamin per day should be provided 2
Monitoring Considerations
- In patients at risk or on treatment with cobalamin, replenishment adequacy should be assessed at least annually by resolution of clinical symptoms and laboratory markers 2
- During initial treatment of pernicious anemia, serum potassium should be closely monitored during the first 48 hours 4
- Monitoring blood potassium should be part of repletion therapy 2
Important Cautions
- There is no established upper toxicity limit for cobalamin, and no reports of acute toxicity in oral or parenteral supplementation 2
- However, excessive provision might be harmful in some populations, such as patients with diabetic nephropathy 2
- Folic acid supplementation can mask vitamin B12 deficiency and should not be given before checking vitamin B12 status 1