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Vitamin B12: the daily reference intake
Vitamin B12 is the nutrient that separates a plant-based diet from a plant-only one, and the nutrient where an older person can eat enough and still run short. EFSA sets an adequate intake of 4 micrograms a day for adults — well above the 2.5 micrograms used on European labels.
These are published population reference values, not a diagnosis and not a prescription. A reference intake describes what covers a healthy group; it cannot tell you your own status, and no page can. Pregnancy, chronic illness, medicines and malabsorption all change the picture — take those questions to a doctor, midwife, pharmacist or dietitian.
Vitamin B12 by age, sex and life stage
EFSA 4 microgram adequate intake is noticeably higher than several older national values, which is why B12 figures quoted from different countries disagree so widely. This page carries the adult values.
| Group | Reference value | Type | Note |
|---|---|---|---|
| Men 19-50 | 4 µg | AI | |
| Women 19-50 | 4 µg | AI | |
| Men 51 and over | 4 µg | AI | |
| Women 51 and over | 4 µg | AI | |
| Adults 65 and over | 4 µg | AI | the number does not change; absorption often does |
| Pregnancy | 4.5 µg | AI | |
| Breastfeeding | 5 µg | AI |
It comes only from animal foods, or from fortification
Vitamin B12 is made by bacteria, not by plants or animals, and it accumulates in animal tissue. No unfortified plant food is a reliable source. Claims for spirulina, nori, tempeh and various mushrooms recur, and mostly involve inactive corrinoid analogues that fill the assay without doing the job — some of which may even interfere with real B12 metabolism.
For anyone eating a fully plant-based diet the conclusion is not controversial and is shared by every national dietetic body: a B12 supplement or reliably fortified foods are required, not optional. That is a statement about a diet, not about a person.
The absorption machinery is elaborate, and it fails with age
B12 has to be released from food protein by stomach acid, bound to intrinsic factor made by the stomach lining, and absorbed by a specific receptor in the terminal ileum. Any step can fail. Atrophic gastritis reduces acid and intrinsic factor and becomes more common with age; pernicious anaemia destroys the intrinsic factor mechanism outright; ileal disease or resection removes the receptor.
The practical result is the striking one: an older adult can eat a diet that supplies far more than 4 micrograms a day and still become deficient, because the food-bound vitamin cannot be released and absorbed. Free B12 in a supplement or fortified food does not need the acid step, which is why supplemental forms often work when food does not.
Metformin and acid-suppressing medicines
Long-term metformin, used for type 2 diabetes, lowers B12 absorption and B12 levels are commonly monitored in people taking it. Long-term proton pump inhibitors and H2 blockers reduce stomach acid and so reduce the release of food-bound B12. Neither is a reason to stop a medicine, and nobody should stop one over a web page — they are reasons to have B12 checked if symptoms appear.
Why deficiency is worth catching early
B12 deficiency causes a large-cell anaemia and, separately, a progressive neurological syndrome: numbness and tingling, unsteady walking, memory and mood changes. The nerve damage can begin before the anaemia is obvious, and can become permanent if it goes on long enough. Folic acid supplementation can hide the blood picture while the nerves continue to deteriorate.
Persistent tingling, unexplained fatigue or unsteadiness deserve a blood test rather than a supplement bought on a hunch. Diagnosis and treatment, including injections where absorption is the problem, belong with a clinician.
The upper level
No tolerable upper intake level has been set for vitamin B12. Absorption via the intrinsic factor route saturates, so a large oral dose is mostly not absorbed, which is also why high-dose oral supplements work for people who cannot absorb it normally: a small fraction crosses by passive diffusion.
Ordinary food against the 4 microgram adult adequate intake
Top of this list: Veal liver, 59.9 µg in a 100 g serving (a small portion) — 1 496% of the 4 microgram adult adequate intake. One serving covers the whole day on its own.
| Food | Ordinary portion | Per portion | Share of the day |
|---|---|---|---|
| Veal liver | a small portion, 100 g | 59.9 µg | 1 496% |
| Mackerel | a fillet, 120 g | 22.8 µg | 570% |
| Canned sockeye salmon | half a tin, 100 g | 5.5 µg | 138% |
| Sardines | half a tin, 60 g | 5.36 µg | 134% |
| Trout | a fillet, 120 g | 4.93 µg | 123% |
| Salmon | a fillet, 120 g | 3.66 µg | 92% |
| Liverwurst spread | on one slice of bread, 25 g | 3.37 µg | 84% |
| Ground beef | a portion, 120 g | 3.28 µg | 82% |
| Canned tuna | a small tin, drained, 100 g | 2.55 µg | 64% |
| Cod | a fillet, 130 g | 1.36 µg | 34% |
| Greek yogurt | a small pot, 150 g | 1.12 µg | 28% |
| 2% milk | a glass, 200 g | 1.06 µg | 27% |
Portion sizes are ordinary household servings chosen for this table, not official reference portions, and the shortlist is an editorial one: everyday foods eaten in this region rather than the highest per-100 g entries in the database. A raw per-100 g ranking would be topped by dried herbs, drink powders and fortified breakfast cereals, which answers a different question. The composition data is American, so where US fortification practice differs from European practice the row carries a dagger and the reason. For the full per-100 g ranking of a nutrient, the food-data section of this site publishes one.
Vitamin B12 for one group at a time
For the full ranking of every food in the database by vitamin b12 per 100 g, see foods highest in vitamin b12.
Sources: EFSA Dietary Reference Values · Regulation (EU) No 1169/2011, Annex XIII · USDA FoodData Central SR Legacy (food composition) · EFSA scientific opinion on dietary reference values for cobalamin, vitamin B12 (2015) · Regulation (EU) No 1169/2011, Annex XIII · checked 2026-09-06
Frequently asked questions
How much vitamin B12 a day?
EFSA adequate intake for adults is 4 micrograms a day, 4.5 in pregnancy and 5.0 while breastfeeding. European labels use 2.5 micrograms, an older and lower reference figure.
Do vegans need a B12 supplement?
Yes. No unfortified plant food is a reliable source of active vitamin B12, and every national dietetic body advises a supplement or reliably fortified foods for a fully plant-based diet.
Why do older adults get B12 deficiency even with a normal diet?
Because releasing B12 from food needs stomach acid and intrinsic factor, and both decline with atrophic gastritis, which becomes more common with age. Supplemental and fortified B12 does not need the acid step.
Does metformin affect vitamin B12?
Long-term metformin reduces B12 absorption, and B12 is commonly monitored in people taking it. That is a reason to have it checked, not a reason to stop the medicine.
See your own numbers, not the population average
TempoLife logs what you eat and adds it up, so you can compare a real week against the reference intake on this page instead of guessing.