Vitamin B12
Contributes to normal functioning of the nervous system and to normal red blood cell formation.
Also known as Cobalamin, Methylcobalamin, Cyanocobalamin, Vit B12, B12
Common doses
500-2500 mcg
Best timing
Morning
Food
With or without food
Interactions
2 known
Vitamin B12 (cobalamin) is a water-soluble vitamin essential for red blood cell formation, neurological function, and DNA synthesis. It is unique among vitamins because it is produced exclusively by microorganisms and is found naturally only in animal products, making deficiency a significant concern for vegans and vegetarians.
B12 deficiency can cause irreversible neurological damage if left untreated, even before anaemia develops. This is particularly dangerous because high folate intake (common in fortified foods) can mask B12-deficiency anaemia while neurological damage continues silently.
Absorption of B12 requires intrinsic factor, a protein produced by the stomach. People with low stomach acid (common in older adults and those taking PPIs) may have impaired B12 absorption from food, even if intake is adequate. Sublingual or high-dose oral supplements can bypass this issue through passive diffusion.
Key benefits
Red blood cell formation
Vitamin B12 contributes to normal red blood cell formation. Deficiency causes megaloblastic anaemia (abnormally large, dysfunctional red blood cells).
Nervous system
Vitamin B12 contributes to normal functioning of the nervous system. It is required for myelin sheath synthesis, which insulates nerve fibres.
Energy metabolism
Vitamin B12 contributes to the reduction of tiredness and fatigue and to normal energy-yielding metabolism.
Homocysteine regulation
B12 (with folate) converts homocysteine to methionine. Elevated homocysteine is a risk factor for cardiovascular disease.
Available forms
Methylcobalamin
The active, methyl-donor form. Preferred by many practitioners. Directly usable in the methionine synthase reaction. Light-sensitive.
Cyanocobalamin
The most common supplement form. Very stable and well-studied. Must be converted to active forms in the body. Contains a trace amount of cyanide (negligible).
Hydroxocobalamin
Used in injections. Longer-lasting in the body than cyanocobalamin. Preferred for clinical B12 deficiency treatment.
Adenosylcobalamin
The mitochondrial form. Used in the methylmalonyl-CoA mutase reaction. Less common in supplements.
Food sources
- Liver and organ meats
- Clams and shellfish
- Beef and lamb
- Fish (salmon, trout, tuna)
- Eggs and dairy
- Fortified nutritional yeast (vegan)
Signs of deficiency
- Fatigue and weakness
- Numbness or tingling in hands and feet
- Balance problems
- Sore, swollen tongue (glossitis)
- Memory problems and confusion
- Mood changes
- Pale or jaundiced skin
Upper intake limit
No established upper limit (NIH). B12 is water-soluble with extremely low toxicity. Excess is excreted in urine. Some people take 1,000+ mcg daily without issues.
Research summary
Strong evidence for treating deficiency and preventing neurological damage. Essential for vegans and recommended for adults over 50 (regardless of diet) due to declining absorption. The methylcobalamin vs cyanocobalamin debate is largely academic; both work. Check serum B12 and MMA levels for accurate assessment of status.
Known interactions (2)
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1 flagZinc and Iron compete for the same absorption pathway. Take at least 2 hours apart.
Supplements
This information is for educational purposes only. It is not medical advice and does not diagnose, treat, cure, or prevent any disease. Always consult a qualified healthcare professional.