Nutrient glossary
What is vitamin B12?
Vitamin B12 keeps nerves insulated and red blood cells forming, and it only occurs naturally in animal foods.
Reviewed 20 July 2026. General information, not medical advice.
The short version
B12 maintains the myelin sheath around nerves and partners folate in making red blood cells and DNA. Deficiency creeps: tiredness and pins and needles first, and nerve damage if it runs on, sometimes masked by high folate intakes.
No plant makes it. Meat, fish, eggs and dairy carry it naturally; vegans need fortified foods or a supplement, no exceptions. Absorption also falls with age and with long-term acid-suppressing medication, so low status is not just a vegan issue.
Daily reference
1.5 µg a day
The UK reference is 1.5 µg a day, which food easily covers for anyone eating animal products. Fully plant-based eaters should supplement regardless of how good the diet looks.
This is the fixed adult reference used across these pages. In the app, your amount adjusts to your body and way of eating.
Best food sources of vitamin B12
Full ranking| Food | Per serving | Per 100g |
|---|---|---|
| Beef Liver | 60 µg | 70.6 µg |
| Mussels | 24 µg | 24 µg |
| Mackerel | 20.9 µg | 19 µg |
| Oysters | 14.9 µg | 17.5 µg |
| Crab | 11.5 µg | 11.5 µg |
| Sardines (canned) | 8.2 µg | 8.9 µg |
| Trout | 5.3 µg | 4.1 µg |
| Salmon Fillet | 4.2 µg | 2.8 µg |
Common questions
- Which plant foods contain B12?
- None naturally. Fortified plant milks, fortified nutritional yeast and supplements are the reliable vegan sources; unfortified seaweed and spirulina are not.
- Why can B12 deficiency take years to appear?
- The liver stores several years of B12, so symptoms surface long after intake stops, which is exactly why new vegans should supplement from day one.