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Vitamin B12 – Essential for Nerves, Blood, and Energy
What is Vitamin B12?
Vitamin B12 (cobalamin) is the most structurally complex of all vitamins and the only one that contains a metal atom (cobalt). It is a water-soluble B vitamin with a unique property: it is produced exclusively by microorganisms (bacteria and archaea). Humans absorb it through animal foods that contain these microorganisms or have accumulated their B12.
Vitamin B12 is primarily known as the "vegan supplement" – and rightly so. People who abstain from animal products will, sooner or later, develop a deficiency without supplementation, which can cause serious and sometimes irreversible neurological damage.
Forms of Vitamin B12
| Form | Characteristics | Recommendation |
|---|---|---|
| Methylcobalamin | Directly bioactive form; particularly good for the nervous system | ⭐⭐⭐⭐⭐ First choice |
| Adenosylcobalamin | Mitochondrial form; good for energy metabolism | ⭐⭐⭐⭐ Good |
| Hydroxocobalamin | Long-term storage form; often in injections | ⭐⭐⭐⭐ Good |
| Cyanocobalamin | Synthetic, stable form; must be converted to methylcobalamin | ⭐⭐⭐ Sufficient, inexpensive |
Why is B12 absorption so complex?
B12 has the most complicated absorption pathway of all vitamins. In foods, it is bound to proteins. In the stomach, hydrochloric acid releases this bond. Then B12 binds to the "intrinsic factor" (a glycoprotein produced by stomach cells). This complex is absorbed in the terminal ileum. Disruptions at any of these steps lead to deficiency:
- Low stomach acid (common in older people, with gastritis)
- Lack of intrinsic factor (pernicious anemia – autoimmune disease)
- Intestinal diseases (Crohn's disease, celiac disease)
- Medications: Metformin, proton pump inhibitors inhibit B12 absorption
Symptoms of B12 deficiency
B12 is stored in the liver for 3–5 years – which is why a deficiency often develops insidiously:
- Exhaustion, weakness, lack of energy
- Megaloblastic anemia (large, immature red blood cells)
- Tingling or numbness in hands and feet (subacute combined degeneration of the spinal cord)
- Cognitive impairments: memory loss, confusion
- Depression, mood swings
- Elevated homocysteine levels (risk of heart disease)
Important: Neurological damage due to B12 deficiency can be irreversible with prolonged undersupply. Recognize and treat early!
Risk groups
| Group | Risk | Recommendation |
|---|---|---|
| Vegans | ⭐⭐⭐⭐⭐ Very high | Mandatory supplement |
| Vegetarians | ⭐⭐⭐ Moderate | Regular testing |
| Over 50 years | ⭐⭐⭐⭐ High (decreasing stomach acid) | Supplement recommended |
| Metformin users | ⭐⭐⭐⭐ High | Supplement + regular tests |
| PPI users (omeprazole etc.) | ⭐⭐⭐ Moderate | Watch out for deficiency |
Dosage
| Goal | Dose | Form |
|---|---|---|
| Prevention (vegans) | 250–1000 µg daily | Methylcobalamin oral |
| Treatment of deficiency | 1000–2000 µg daily | Oral or injection |
| Weekly intake | 2000–2500 µg 2×/week | Cyanocobalamin possible |
At very high oral doses (>200 µg), B12 is also absorbed without intrinsic factor through passive diffusion – this explains why high-dose oral supplements can also work for absorption problems.
Frequently Asked Questions (FAQ)
How often should I have my B12 level tested?
Vegans: At least once a year. The best marker is holotranscobalamin (active B12) or methylmalonic acid in urine – not just serum B12, which often appears normal despite deficiency.
Can I get B12 from algae?
Nori and some other algae contain B12 analogs that appear like real B12 in tests but are biologically inactive. They can even block real B12. Do not rely on them as a B12 source!
Related terms
B-Complex · Folic acid · Iron · Omega-3
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