B12 deficiency is sneaky. Symptoms develop slowly and can mimic other conditions. Vegans are at highest risk, but so are people over 50, those on metformin or PPIs, and anyone with absorption issues.
B12 Forms
Methylcobalamin - Active, methylated form - Used directly by the body - May be better for those with MTHFR variants - Slightly more expensive
Cyanocobalamin - Synthetic, must be converted - Most studied form - More stable (better shelf life) - Works fine for most people
Adenosylcobalamin - Another active form - Less common in supplements - Used by mitochondria
Hydroxocobalamin - Used in injections - Longer-lasting than cyano - Less common in pills
Where to Find B12
Standalone B12 - Best for treating deficiency - 500-5000mcg common - Sublingual dissolves under tongue (may bypass absorption issues)
B-Complex - All 8 B vitamins together - Usually 50-500mcg B12 - Good for general support
Multivitamins - Should include 25-100mcg - Often cyanocobalamin - May be enough for maintenance
Vegan supplements - Fortified with B12 - Nutritional yeast often contains added B12 - Essential for plant-based diets
Who Really Needs B12
Definitely need to supplement: - Vegans (no exceptions) - Vegetarians not eating eggs/dairy daily - Anyone over 50 (absorption decreases with age) - Those on metformin, PPIs, or H2 blockers - People with Crohn's, celiac, or gastric surgery
Symptoms of deficiency: - Fatigue, weakness - Numbness/tingling in hands and feet - Difficulty walking - Mood changes, depression - Memory problems
Testing: Serum B12 plus methylmalonic acid (MMA) gives the full picture. Serum B12 alone can miss functional deficiency.