Vitamin B12: Complete Guide
Essential for energy, nerves, and blood cells. 20% of adults over 60 are deficient. Vegans need this.
Quick Summary
Essential for energy, nerves, and blood cells. 20% of adults over 60 are deficient. Vegans need this. 500-1000mcg daily or 2500mcg weekly. Best form: Methylcobalamin.
What is Vitamin B12?
B12 (cobalamin) is a water-soluble vitamin needed for DNA synthesis, red blood cell formation, and nerve function. It's only naturally found in animal foods. Your body stores it for years, so deficiency develops slowly and sneakily.
Who Should Consider Vitamin B12?
- Vegans and vegetarians (no plant sources)
- Adults over 50 (absorption decreases with age)
- People on metformin (depletes B12)
- Those with digestive issues (malabsorption)
- Anyone with fatigue, brain fog, or numbness/tingling
How It Works
B12 acts as a cofactor for enzymes involved in DNA synthesis and methylation. It's required for converting homocysteine to methionine (important for heart health) and for maintaining the myelin sheath around nerves. Deficiency causes irreversible nerve damage if prolonged.
Forms Comparison
Different forms of Vitamin B12 have varying absorption rates and best uses. Here's how they compare:
| Form | Bioavailability | Best For |
|---|---|---|
| Methylcobalamin | 50% | Active form. No conversion needed. Preferred for most. |
| Cyanocobalamin | 45% | Most stable and studied. Body converts to active forms. |
| Adenosylcobalamin | 50% | Mitochondrial form. Sometimes combined with methyl. |
| Hydroxocobalamin | 55% | Injection form. Longest retention time. |
Our recommendation: Methylcobalamin for most people due to superior absorption and tolerability.
Benefits & Evidence
Vitamin B12 has 3 strongly-evidenced benefits and 1 moderately-evidenced benefits.
Energy levels
strong evidenceResolves fatigue caused by B12 deficiency
Nerve function
strong evidencePrevents/treats peripheral neuropathy
Cognitive function
strong evidenceDeficiency causes brain fog, memory issues
Heart health
moderate evidenceLowers homocysteine (cardiovascular risk marker)
Dosing & Timing
Recommended Doses
Timing
Side Effects & Interactions
Possible Side Effects
- Essentially none. Very safe
- Acne (rare, high doses). Rare
Interactions to Know
- Metformin reduces B12 absorption (supplement if on metformin)
- PPIs and H2 blockers reduce absorption
- Generally safe with all supplements
Frequently Asked Questions
Both work. Methyl is the active form (no conversion needed). Cyanocobalamin is cheaper and more stable. For most people, doesn't matter. MTHFR gene variants may do better with methyl.
Ingredient Analysis Pages
Full evidence-based analysis for each form and variant:
Related Topics
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About this information: Our analysis of Vitamin B12 is based on peer-reviewed research from PubMed, ClinicalTrials.gov, and NIH databases. These statements have not been evaluated by the FDA. Supplements are not intended to diagnose, treat, cure, or prevent any disease.
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