How much B12 should a vegan take?

Either 50–250 µg of cyanocobalamin daily or 2,000 µg weekly. Both maintain normal status in healthy adults.

Can I get B12 from fortified foods alone?

Yes, if you eat three fortified servings a day with labelled microgram amounts — but a tablet is cheaper and more reliable.

How often should I test?

Once at the start and then every one to two years, or sooner with tingling, fatigue or cognitive symptoms. Ask for MMA if results are borderline.

Is cyanocobalamin safe?

Yes. The cyanide moiety is trivial in size and cyanocobalamin is the most stable, best-studied and cheapest form.

Do children need B12 too?

Yes — dosing is age-scaled, usually via fortified foods plus a paediatric supplement; ask a paediatric dietitian.

All guidesNutrition science7 min read

Vitamin B12: the one supplement, explained without hand-waving

B12 is made by bacteria, not by animals or plants. Here is why supplementation is the honest answer, what dose works, and how to test.

In short

B12 is synthesised by microbes; farmed animals are routinely supplemented, so much of the world's B12 supply already comes from a factory.
Reliable vegan sources are supplements and fortified foods — not seaweed, tempeh, mushrooms or unwashed produce.
A common effective regimen is 50–250 µg daily or 2,000 µg weekly of cyanocobalamin.
Deficiency develops slowly and can cause irreversible neurological damage, which is why testing beats guessing.

Key numbers

2.4 µg

Adult reference daily intake

EFSA / NIH

2,000 µg

Typical weekly cyanocobalamin dose

Clinical practice

3–5 years

Liver stores before deficiency appears

NIH ODS

20%+

Share of over-60s with low B12 regardless of diet

NIH ODS

Where B12 actually comes from

Only bacteria and archaea synthesise cobalamin. Ruminants absorb it from gut microbes; monogastric farmed animals get it from fortified feed. Roughly 90% of global B12 production is fed to livestock, so an omnivore diet is often supplemented B12 taken indirectly.

Sources that do not work

Spirulina, nori, tempeh, kombucha, mushrooms and organic soil residues contain B12 analogues that can register on some assays without being biologically active — and inactive analogues may even compete with real B12 at the receptor. Do not rely on them.

Reliable: cyanocobalamin or methylcobalamin tablets, B12-fortified plant milks, nutritional yeast labelled as fortified, fortified cereals.
Unreliable: algae, fermented foods, unwashed vegetables, 'natural' B12 claims without a labelled microgram figure.

Dose, and why weekly works

Absorption through intrinsic factor saturates near 1.5–2 µg per dose, after which a small percentage crosses passively. That is why a 2,000 µg weekly tablet and a 50 µg daily tablet both maintain status: infrequent large doses lean on passive diffusion.

Testing without being misled

Serum B12 alone is a weak marker. Methylmalonic acid (MMA) and homocysteine reflect functional status better; ask for MMA if symptoms or borderline results appear. Folate supplementation can mask the anaemia while nerve damage continues, which is the reason for the neurological caution.

The data

Absorbed B12 from a single oral dose (approximate)

1 µg dose0.5 µg absorbed · ~50%
10 µg dose1.6 µg absorbed
500 µg dose5 µg absorbed
2000 µg dose20 µg absorbed · passive

At a glance

Common regimens and what they suit

Regimen	Form	Best for	Notes
50–250 µg daily	Cyanocobalamin	Most adults	Cheapest, most robust
2,000 µg weekly	Cyanocobalamin	People who forget daily pills	Relies on passive absorption
3 × fortified foods daily	Fortified	Children, light supplement users	Check the label microgram figure
1,000 µg daily	Methylcobalamin	Diagnosed deficiency, under supervision	Doctor-guided
Injections	Hydroxocobalamin	Absorption disorders	Prescription only

Common objections

ClaimIf a diet needs supplements it must be unnatural.

What the evidence showsFarmed animals are supplemented too, and iodised salt, fortified flour and vitamin D are standard across omnivore diets. A tablet is a delivery method, not a verdict.

ClaimSpirulina covers B12.

What the evidence showsIt supplies inactive analogues that do not correct deficiency and can distort test results.

ClaimYou only need B12 if you feel tired.

What the evidence showsNeurological damage can precede symptoms and can be permanent; steady low-cost supplementation avoids the gamble entirely.

Questions people ask

How much B12 should a vegan take?: Either 50–250 µg of cyanocobalamin daily or 2,000 µg weekly. Both maintain normal status in healthy adults.
Can I get B12 from fortified foods alone?: Yes, if you eat three fortified servings a day with labelled microgram amounts — but a tablet is cheaper and more reliable.
How often should I test?: Once at the start and then every one to two years, or sooner with tingling, fatigue or cognitive symptoms. Ask for MMA if results are borderline.
Is cyanocobalamin safe?: Yes. The cyanide moiety is trivial in size and cyanocobalamin is the most stable, best-studied and cheapest form.
Do children need B12 too?: Yes — dosing is age-scaled, usually via fortified foods plus a paediatric supplement; ask a paediatric dietitian.

Sources

Figures are drawn from the sources listed at the end of this guide.

Text on this page is free to reuse under CC BY 4.0 with attribution to Veg.ac.

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