Recommended Dosage of Vitamin B12 for Mental Health
For mental health concerns, vitamin B12 should be administered at a dose of 1 mg (1000 mcg) daily orally for most adults with suspected or confirmed deficiency, while intramuscular administration of 1 mg hydroxocobalamin should be used for severe deficiency or neurological symptoms. 1
Assessment of B12 Status
Before supplementation, proper assessment is crucial:
- Initial laboratory assessment should include complete blood count and serum vitamin B12 level
- Serum methylmalonic acid measurement should confirm deficiency in asymptomatic high-risk patients with low-normal B12 levels
- B12 deficiency is defined as:
- Severe deficiency: <150 pmol/L (associated with cognitive impairment)
- Subclinical deficiency: <250 pmol/L (associated with neuropsychiatric conditions)
Dosing Protocol Based on Clinical Presentation
For Patients with Neurological Involvement
- Hydroxocobalamin 1 mg intramuscularly on alternate days until no further improvement
- Then maintenance with 1 mg intramuscularly every 2 months 2
- Urgent specialist referral to neurologist and hematologist is recommended
For Patients without Neurological Involvement
- Hydroxocobalamin 1 mg intramuscularly three times a week for 2 weeks
- Then maintenance with 1 mg intramuscularly every 2-3 months for life 2
- Alternatively, oral high-dose vitamin B12 (1-2 mg daily) is equally effective for correcting deficiency 1
Special Populations and Considerations
- Adults over 75 years: Should be screened for B12 deficiency due to higher prevalence
- Vegetarians/vegans: Require regular B12 supplementation (1 mg daily)
- Post-bariatric surgery patients: Need 1 mg oral vitamin B12 daily indefinitely 1
- Patients taking metformin (>4 months) or acid suppressants (>12 months): Consider screening and supplementation
Evidence for Mental Health Benefits
While the evidence specifically for mental health outcomes is limited:
- B12 deficiency is associated with depression, cognitive impairment, and other neuropsychiatric symptoms 3
- Supplementation improves cognition only in patients with pre-existing B12 deficiency (<150 pmol/L) 4
- No high-quality evidence supports routine B12 supplementation for psychiatric disorders in the absence of deficiency 3
Important Caveats
- Always rule out B12 deficiency before initiating folate supplementation, as folate may mask B12 deficiency and precipitate neurological damage 2
- European guidelines suggest higher daily intake requirements (4-7 μg/day) than UK recommendations (1.5 μg/day) 2
- Testing for B12 deficiency should be considered for atypical or severe psychiatric presentations 3
- Approximately 10% of psychiatric patients may have low B12 levels, often due to nutritional insufficiency 5
B12 supplementation is safe and inexpensive, making it a reasonable intervention for those with confirmed or suspected deficiency presenting with mental health concerns, but it should not be viewed as a primary treatment for psychiatric disorders in the absence of deficiency.