Recommended Daily Allowance of Vitamin B12
The recommended daily allowance (RDA) of vitamin B12 for adults is 2.4 micrograms per day according to the World Health Organization guidelines. 1
General Requirements
Vitamin B12 (cobalamin) is an essential water-soluble vitamin that plays crucial roles in:
- Red blood cell formation
- Neurological function
- DNA synthesis
The daily requirements vary slightly by population:
- Adults (general population): 2.4 μg/day
- Pregnant women: 2.6 μg/day
- Lactating women: 2.8 μg/day
- Children: 0.5-3 μg/day (age-dependent) 2
Special Considerations for Different Populations
Older Adults (>50 years)
- Should obtain B12 primarily from supplements or fortified foods rather than naturally occurring food sources
- This is due to age-related decline in gastric acid production (atrophic gastritis) affecting protein-bound B12 absorption 3
- Crystalline B12 (the form in supplements and fortified foods) is better absorbed in this population
Vegetarians and Vegans
- Must take B12 supplements regularly as plant foods do not naturally contain vitamin B12
- Even vegetarians who consume dairy and eggs should monitor their B12 status 2
Post-Bariatric Surgery Patients
- Should receive 1 mg of oral vitamin B12 daily indefinitely 4
Patients with Inflammatory Bowel Disease (IBD)
- Patients with Crohn's Disease who have had >20 cm of distal ileum resected require vitamin B12 supplementation
- Recommended dose: 1000 μg (1 mg) intramuscularly monthly for life 1
Patients on Certain Medications
- Those taking methotrexate, sulphasalazine, proton pump inhibitors, or histamine H2 blockers for extended periods require monitoring and possible supplementation 1, 4
Treatment of B12 Deficiency
When deficiency is identified:
For patients without neurological symptoms:
- Hydroxocobalamin 1 mg intramuscularly three times weekly for 2 weeks
- Followed by maintenance with 1 mg intramuscularly every 2-3 months lifelong 1
For patients with neurological involvement:
- Hydroxocobalamin 1 mg intramuscularly on alternate days until no further improvement
- Then 1 mg intramuscularly every 2 months 1
Oral high-dose therapy:
- Daily doses of 647-1032 μg have been shown to normalize mild B12 deficiency 5
- This is more than 200 times the standard RDA
Important Cautions
- Folic acid supplementation can mask B12 deficiency symptoms while neurological damage continues
- Daily intake of folic acid should not exceed 1000 μg (1.0 mg) unless prescribed by a physician 1
- High serum folate during B12 deficiency may actually worsen anemia and cognitive symptoms 6
Monitoring
For patients at risk of deficiency, monitoring should include:
- Serum vitamin B12 levels
- Methylmalonic acid (MMA) levels (more sensitive marker)
- Complete blood count
- Homocysteine levels when appropriate
Remember that neurological symptoms may occur even without anemia, so early identification and treatment are essential for preventing irreversible neurological damage.