Vitamin B12 on a vegan diet: the one supplement that is not optional
B12 is made by bacteria, not by plants or animals. Grazing animals get it from soil microbes or from supplemented feed; most farmed animals are given B12 in their feed directly. Taking it as a supplement simply removes the animal from the middle of that chain. The dose is larger than the RDA because absorption via the intrinsic-factor route saturates at a few micrograms per dose, with only about 1% of the rest absorbed passively.
Key facts
- Tlen ticnequi īpan cē tonalli
- 4 mcg
- Tlamantli tlen ticcuah tlen ōmochīuh
- 9
- Tlen quipia miac
- Cyanocobalamin tablet — 100 mcg
- Tlen ticcuah
- The simplest reliable routine
Quexquich ticnequi
Vegan Society / Vegan Health consensus
Equivalent absorbed dose via passive diffusion
Requires consistency; supplements are more reliable
Reduced stomach acid impairs release and absorption
Infant stores depend entirely on maternal status
Canin huītz
| Tlacualli | Tlaqualli | mcg | % tlen ticnequi |
|---|---|---|---|
| Cyanocobalamin tabletRoughly 2–5 mcg is actually absorbed | 1 tablet | 100 | 2500% |
| Fortified nutritional yeastOnly if the label says B12 added | 2 tbsp (5 g) | 5 | 125% |
| Fortified soy milk | 250 ml | 1 | 25% |
| Fortified oat milkMany organic brands are not fortified | 250 ml | 1 | 25% |
| Fortified breakfast cereal | 40 g | 1 | 25% |
| Fortified meat alternativesBrand-dependent — check the panel | 100 g | 1 | 25% |
| Fortified vegan spread | 10 g | 0.5 | 13% |
| Spirulina, chlorella, noriContains inactive analogues that can mask deficiency | any | 0 | 0% |
| Tempeh, kombucha, sauerkrautUnreliable and usually analogue only | any | 0 | 0% |
Tlen ticcelia, ahmo san tlen ticcuah
Big doses absorb badly, which is why the dose looks huge
The active transport route handles only about 1.5–2 mcg per dose and then saturates for several hours. Above that, roughly 1% crosses passively. A 1,000 mcg tablet therefore delivers around 10 mcg — the arithmetic behind every 'why so much?' question.
Chewable and sublingual are not magic, but they help
Trials show sublingual and oral tablets perform similarly in people with normal absorption. Chewing does help if you have low stomach acid or take a proton-pump inhibitor.
Cyanocobalamin is the best-evidenced form
It is the most stable and the form used in almost every trial. Methylcobalamin is fine but degrades faster in light and needs higher doses. People with kidney failure or the rare Leber's optic atrophy should use hydroxocobalamin or methylcobalamin instead.
The simplest reliable routine
One 2,000 mcg cyanocobalamin tablet, chewed, once a week — cheap, hard to forget and hard to overdose, since excess is excreted in urine. If you prefer daily, 100 mcg is plenty. Add a second source if you are over 50, pregnant, breastfeeding or on metformin or a PPI.
Tlen quimati īcuac ahmo ticpiya miac
- Tingling or numbness in hands and feet (early nerve involvement)
- Fatigue and breathlessness from macrocytic anaemia
- Memory problems, brain fog, low mood or irritability
- Sore, smooth, red tongue and mouth ulcers
- Unsteady walking and poor balance in advanced cases
- High-folate diets can mask the anaemia while nerve damage continues
Tlen monequi tictequipachoa
- Serum B12
- Cheap and widely available, but unreliable alone — analogues inflate it and levels under about 300 pmol/L can still be functionally low.
- Methylmalonic acid (MMA)
- The best functional marker. Elevated MMA means B12 is genuinely lacking at the cellular level.
- Homocysteine
- Rises in B12, folate or B6 deficiency; useful alongside MMA, not on its own.
- Full blood count
- Enlarged red cells (high MCV) hint at deficiency but appear late and are hidden by high folate intake.
Tlen monequi ticchīhua cualli
Trusting algae or fermented foods
Spirulina and nori contain corrinoid analogues that bind B12 receptors without doing the job, and can make blood tests look better than reality.
Stopping because a test came back normal
A normal result reflects a working supplement, not a diet that no longer needs one. Stores can last years, which is exactly why deficiency creeps up unnoticed.
Assuming plant milk is fortified
Organic ranges in the EU are frequently unfortified because organic rules restrict added vitamins. Read the panel each time you change brand.
Tlahtoltin tlen tlācatl quitemoa
Can you get B12 from plants?
Not reliably. B12 comes from bacteria; the traces found on unwashed produce or in fermented foods are inconsistent and often inactive analogues. Fortified foods and supplements are the only dependable vegan sources.
How long before deficiency shows up?
The liver stores two to five years' worth, so someone who stops all sources may feel fine for a long time and then develop neurological symptoms. Do not use 'I feel fine' as evidence.
Can you take too much B12?
There is no established upper limit; excess is water-soluble and excreted. Very high doses can cause acne in some people, and people with kidney disease should discuss dosing with a clinician.
Do meat eaters need B12 too?
Many get it supplemented indirectly, since livestock feed is routinely fortified with cobalt or B12. Deficiency is also common in older omnivores because of reduced absorption, not intake.
Is B12 in toothpaste or spray better absorbed?
Sprays and lozenges work about as well as tablets in people with normal absorption. Pick whichever you will actually take every week.
Tlamachiyōtl
Occequīntin tlamachiyōtl tlen ticcuah
Reviewed 2026-08-23 by the Veg.ac editorial team · Data: NIH ODS — Vitamin B12 fact sheet · Free to reuse under CC BY 4.0 with a link back.
Tlamachiyōtl tlen ahmo quimati tlen tictequipachoa. Xicnotza cē tlamachiyōtl ahnozo cē tlamachiyōtl ītechcopa tlen tictequipachoa.