Do you need to take B12 on a vegan diet?

Yes, and it is the least disputed recommendation in all of plant-based nutrition. B12 is not reliably present in unfortified plant foods, and its deficiency can leave neurological damage that does not always reverse. On a vegan diet the supplement is not an extra: it is part of the diet.

How much B12 should you take?

The EU reference value is 2.5 micrograms a day, but supplements carry much more (500 or 1000 micrograms) because absorption saturates and only a fraction of a high dose is used. That is why both small daily regimes and large weekly ones work. The specific regime is best adjusted with a professional.

Is methylcobalamin or cyanocobalamin better?

Both correct deficiency. Cyanocobalamin is the most studied, most stable and cheapest form; methylcobalamin is sold as the active form, without that translating into a clear advantage at usual doses. If price decides, cyanocobalamin.

How do you know if you are short of B12?

With a blood test, ideally including more than blood B12: homocysteine or methylmalonic acid detect insufficient intake earlier. Tiredness or tingling are late, non-specific symptoms. The interpretation is for a doctor.

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Vitamin B12 · Strong evidence

What vitamin B12 is for and who needs to take it

The short answer. B12 is the one vitamin that cannot be reliably obtained from a 100 % plant diet: it is found in animal foods and fortified products. Deficiency takes years to appear because the liver keeps reserves, and when it does appear it can leave neurological damage. That is why it is this site’s exception to "first check whether you lack it": on a vegan diet the supplement is part of the diet, not an extra.

Several meta-analyses or position stands from scientific societies agree that there is an effect. No figure on this page is attributed to a specific product: the effect belongs to the ingredient and every number carries its source next to it.

01 What it does and how much

Each row is a measured effect, with the figure the study gives and the source number. Where the evidence gives no figure, the column says so instead of making up a percentage.

Effects of vitamin B12 with their source
Effect	How much	Detail
EU daily reference value	2.5 micrograms	The labelling NRV. Supplements carry much higher doses (500 or 1000 micrograms) because absorption saturates and only a small fraction of each dose is used. [1]
Functions authorised in the EU	red blood cells, energy and tiredness	It contributes to normal red blood cell formation, normal energy metabolism, normal nervous system function and reduced tiredness. [2]
Deficiency prevalence in vegetarians and vegans	high	The review summarising the studies finds frequent deficiency in those who do not supplement, more so the stricter and longer the diet. [3]
Liver reserves	years	That is the trap: you can go a long time without intake and without symptoms. When they appear, part of the neurological damage may not reverse. [3]

02 How to take it

Dose. On a vegan diet, the usual approach is a high weekly dose or a smaller daily one. Adjust it with whoever manages your case.
When. The time does not matter. Sublingual forms have not been shown to be better than swallowing it.
How long before you notice it. Reserves refill over weeks or months.

Details that change the result

The higher the dose, the lower the percentage absorbed: that is why tubs carry hundreds of times the reference value and it is not a mistake.
Cyanocobalamin and methylcobalamin both work; cyanocobalamin is the most studied and the cheapest.
Nutritional yeast, algae and tempeh are not reliable sources unless they are fortified and say so.
From age 60, absorption drops even if you eat meat, and it is worth checking then too.

03 When it makes sense and when it does not

Worth it if

Vegan diet: here it is not optional.
Vegetarian diet with little dairy and few eggs.
Over 60s or absorption problems, with medical follow-up.
Long-term treatment with metformin or proton pump inhibitors, which are linked to lower levels.

Not worth it if

As an energiser in someone who eats meat and has normal levels.
Relying on unfortified algae or yeast as a source.
Never checking it, if you have been on a strict plant diet for years.

04 Sources

Every figure above comes from here. They are position stands from scientific societies, meta-analyses and peer-reviewed reviews: if a claim cannot hang from one of these lines, it is not on the page. References are cited in their original form.

Reglamento (UE) 1169/2011, Anexo XIII: valores de referencia de nutrientes. Vitamina B12, 2,5 microgramos. https://eur-lex.europa.eu/legal-content/ES/TXT/?uri=CELEX%3A32011R1169
Reglamento (UE) 432/2012: declaraciones autorizadas. La vitamina B12 contribuye a la formacion normal de globulos rojos, al metabolismo energetico normal, al funcionamiento normal del sistema nervioso y a disminuir el cansancio y la fatiga. https://eur-lex.europa.eu/legal-content/ES/TXT/?uri=CELEX%3A32012R0432
Pawlak R et al. How prevalent is vitamin B12 deficiency among vegetarians? Nutr Rev. 2013;71(2):110-117. doi:10.1111/nure.12001

This is not medical advice. It is what some studies say about an ingredient, not a protocol for you. With an illness, medication or pregnancy involved, the decision belongs to a healthcare professional who knows you.

Questions about vitamin B12

Answered with the data on this page

Do you need to take B12 on a vegan diet?: Yes, and it is the least disputed recommendation in all of plant-based nutrition. B12 is not reliably present in unfortified plant foods, and its deficiency can leave neurological damage that does not always reverse. On a vegan diet the supplement is not an extra: it is part of the diet.
How much B12 should you take?: The EU reference value is 2.5 micrograms a day, but supplements carry much more (500 or 1000 micrograms) because absorption saturates and only a fraction of a high dose is used. That is why both small daily regimes and large weekly ones work. The specific regime is best adjusted with a professional.
Is methylcobalamin or cyanocobalamin better?: Both correct deficiency. Cyanocobalamin is the most studied, most stable and cheapest form; methylcobalamin is sold as the active form, without that translating into a clear advantage at usual doses. If price decides, cyanocobalamin.
How do you know if you are short of B12?: With a blood test, ideally including more than blood B12: homocysteine or methylmalonic acid detect insufficient intake earlier. Tiredness or tingling are late, non-specific symptoms. The interpretation is for a doctor.

And now, which to buy

Prices, kept apart from the evidence

This page explains what vitamin B12 does and deliberately names no brand. The comparison is the other half: 106 products from 9 stores from €0.025 per capsule, sorted by price and by how verifiable their certification is.

See the vitamin b12 comparison

Other guides

What each supplement does, with its sources