Quick answer
- The NHS says adults need about 1.5 µg a day, that vegans may not get enough, and that 2 mg (2,000 µg) or less a day from supplements is unlikely to cause harm.
- Vegans need a B12 supplement or fortified foods; older adults and people on metformin or acid-reducing medicines are also at risk of low B12.
- Labels show high doses because absorption drops sharply above 1–2 µg: from about 50% of a small dose to about 1.3% of 1,000 µg.
- There is no evidence that methylcobalamin is absorbed better than cyanocobalamin, according to the US National Institutes of Health.
- No safe upper level has been set: B12 has low toxicity. Tiredness only improves if you were low to begin with.
Key numbers
- UK daily need (NHS)
- 1.5 µg/day
- UK figure for supplements (NHS)
- 2 mg/day or less
- Unlikely to cause harm.
- Reference intake on labels (NRV)
- 2.5 µg/day
- Adequate intake, adults (EFSA)
- 4 µg/day
- Safe upper level
- Not set
- Low potential for toxicity.
- Absorbed from a 1,000 µg dose
- ~1.3% (about 13 µg)
- Minimum for an authorised claim
- 0.375 µg per daily dose
What these terms mean: NRV upper levels (NHS, EFSA) maximum levels by country daily dose
How to choose
- Decide why you take it: vegan diet, age over about 50, metformin or long-term acid blockers are the usual reasons. Otherwise you probably get enough from food.
- Check the µg per daily dose. Low daily doses work because absorption is efficient; high doses rely on the small share absorbed without intrinsic factor.
- Cyanocobalamin is the most studied and cheapest form; methylcobalamin costs more without proven extra benefit.
- Chewable or sublingual tablets are fine; there is no need for injections unless a doctor prescribes them.
- If you take a B complex or multivitamin, check whether it already covers B12.
Vitamin B12 forms compared
| Form | What it is | Good to know |
|---|---|---|
| Cyanocobalamin | The standard synthetic form | Most studied, stable and cheap |
| Methylcobalamin | An active form found in the body | No proven absorption advantage; costs more |
| Hydroxocobalamin | The form used in injections | Mostly in medicines, rarely in supplements |
| Adenosylcobalamin | Another active form | Often combined with methylcobalamin; little extra evidence |
What the evidence says
B12 comes almost only from animal foods, so a vegan diet without supplements or fortified foods eventually leads to deficiency. With age, stomach acid and intrinsic factor often fall, which makes B12 from food harder to absorb; supplements are absorbed better because the vitamin is not bound to food protein.
Absorption depends on the dose: at around 1–2 µg, about half is absorbed; at 500 µg about 2%, and at 1,000 µg about 1.3%, according to the US National Institutes of Health. Extra B12 reduces tiredness only if you were low; read our guide to supplement labels to compare doses and %NRV.
What the label may legally claim
Authorised claims (GB and EU registers)
- Contributes to the reduction of tiredness and fatigue
- Contributes to normal energy-yielding metabolism and normal red blood cell formation
- Contributes to normal functioning of the nervous system and normal psychological function
- Contributes to normal function of the immune system (all from 0.375 µg per daily dose)
Not authorised in GB or the EU
- More energy if you are not deficient
- Better memory
- Weight loss
How health claims work (UK & EU): health claims
Products we have checked
Label data checked by NutriMetrics for products sold in Spain and Germany. UK product checks are next. Sorted alphabetically, not ranked.
Who should be careful
- Symptoms of deficiency (numbness, tingling, anaemia, memory problems) need a diagnosis, not just a supplement. See a doctor.
- Folic acid can mask B12 deficiency, so do not take high doses of folic acid alone if your B12 might be low.
- Blood tests: supplements raise blood B12 for a while; mention them before testing.
FAQ
Who needs vitamin B12 supplements?
Vegans and some vegetarians, older adults (who often absorb less), people with digestive conditions or stomach surgery, and people taking metformin or acid-reducing medicines for a long time.
Is methylcobalamin better than cyanocobalamin?
There is no evidence that absorption differs between forms. Cyanocobalamin is the most studied and usually the cheapest.
Is 1,000 µg of B12 too much?
No safe upper level has been set, because B12 has low toxicity. Only about 1.3% of a 1,000 µg dose is absorbed, which is why such doses exist.
Sources
- NHS — B vitamins and folic acid
- DHSC — Great Britain nutrition and health claims (NHC) register
- NIH Office of Dietary Supplements — Vitamin B12 fact sheet for health professionals
- EFSA — Dietary reference values
- European Commission — EU Register of nutrition and health claims
- Commission Regulation (EU) No 432/2012 — list of permitted health claims
Information only, not medical advice. No product on this page is a paid placement.