Nutrients ·
Vegan B12: forms, doses and how to know you're covered
The short answer
Vegans need a reliable B12 source because plants don't make it. Common approaches are a daily supplement (often 25–100 mcg), a weekly higher dose, or fortified foods eaten two to three times a day. Cyanocobalamin is the most studied and stable form; methylcobalamin also works.
Why B12 is different
B12 is produced by microorganisms. Animals get it from bacteria and feed; humans eating plants get almost none unless foods are fortified. The body stores B12 for years, so a shortfall can be silent for a long time.
Forms
- Cyanocobalamin — the most researched, very stable, converted by the body into active forms.
- Methylcobalamin and adenosylcobalamin — active forms; effective, less shelf-stable.
- Hydroxocobalamin — used mostly in injections.
How much
The adult recommended intake is 2.4 mcg a day (NIH). Only a small fraction of a large oral dose is absorbed, which is why supplements are often 25–1,000 mcg. A clinician can tailor the dose, especially if levels are already low.
Testing
Serum B12 alone can look normal while stores are low. Methylmalonic acid (MMA) or holotranscobalamin are more sensitive markers. Ask for them if you've been plant-based for years.
Sources besides pills
Fortified plant milks, breakfast cereals and nutritional yeast can supply B12 — check the label for amounts. Seaweed, spirulina and fermented foods are not reliable sources.
See the rest of the plant-based essentials in our beginner's guide.
Questions
- Is methylcobalamin better than cyanocobalamin?
- Not clearly. Both raise B12 levels. Cyanocobalamin is more stable and has the most research; methylcobalamin is a reasonable alternative.
- Can spirulina provide B12?
- No. Spirulina contains B12 analogues that the body can't use and may interfere with tests.
- Can you take too much B12?
- No upper limit has been set because excess is excreted, but very high doses aren't needed for most people.
From the shop
This article is for general information and isn't medical advice. These statements have not been evaluated by the Food and Drug Administration. Products are not intended to diagnose, treat, cure or prevent any disease. Talk to a healthcare professional before starting a supplement, especially if you are pregnant, nursing or take medication.