Where Does Plant-Based B12 Come From? Uncovering Vegan Sources

December 24, 2025 •

4 min read

According to The Vegan Society, the only reliable vegan sources of B12 are foods fortified with the vitamin and B12 supplements, as the nutrient is produced by microorganisms and not plants. This makes understanding the true source of B12 vital for those following a plant-based lifestyle.

Quick Summary

Vitamin B12 is synthesized by bacteria and reliably obtained on a plant-based diet through fortified foods and supplements, as natural plant sources contain none or inactive forms of the nutrient.

Key Points

Microbial Origin: Vitamin B12 is produced by bacteria and archaea, not by plants or animals directly.
Supplements are Reliable: B12 supplements, created through bacterial fermentation, provide a consistent and safe dose.
Fortified Foods are Key: Many plant milks, cereals, and nutritional yeasts are fortified with usable B12 and are reliable sources.
Avoid Inactive Analogues: Foods like spirulina, nori, and some fermented products are unreliable and can contain inactive B12 analogues that interfere with absorption.
Proactive Strategy: A proactive approach with fortified foods and/or supplements is necessary for vegans to prevent B12 deficiency.
No Special Status: The B12 used in supplements and fortified foods is the same microbial B12 found naturally in animal products.

The Microbial Origin of Vitamin B12

Contrary to popular belief that meat is the ultimate source of B12, the vitamin is not produced by plants or animals but by specific bacteria and archaea. This makes vitamin B12 unique among the essential vitamins. Animals, including cattle and other herbivores, acquire B12 from the microorganisms naturally present in their environment, their food, and their digestive systems. Humans historically might have acquired some B12 from less sanitary food preparation, but modern hygiene standards and water treatment have eliminated this unreliable source. For those on a vegan diet, replicating the intake of B12 through contaminated sources is neither safe nor necessary.

Unreliable "Natural" Plant Sources

Some plant-based items have been touted as natural B12 sources, but the scientific evidence does not support these claims for reliable intake. The primary issue is the presence of B12 analogues, or "false B12," which can interfere with true B12 metabolism and may even show up inaccurately on blood tests. For this reason, it is risky to depend on these sources.

Spirulina and Algae: While some algae species contain B12, the amount can vary greatly, and they often contain high levels of inactive B12 analogues. Relying solely on these could mask a deficiency while failing to provide the body with usable B12.
Nori (Dried Seaweed): Similar to other algae, dried nori has been shown to contain biologically inactive B12 compounds in addition to usable B12. Some studies have found it can contain active B12, but levels are inconsistent, making it an unreliable primary source.
Mushrooms: Edible mushrooms like dried shiitake can contain small, highly variable amounts of B12, which are likely absorbed from microorganisms in their growth substrate. However, the amounts are typically insufficient to meet daily needs.
Fermented Foods (e.g., Tempeh): The fermentation process can sometimes introduce B12 from bacteria, but this is an uncontrolled process and the resulting B12 content is often negligible and unreliable.

Reliable Vegan Sources of B12

For vegans, ensuring adequate B12 intake requires a proactive approach using scientifically validated methods. These methods involve B12 that is created in a controlled, sterile environment using bacterial fermentation. The resulting B12 is then added to foods or supplements.

B12 Supplements

This is often considered the most foolproof and convenient method. B12 supplements are widely available in several forms, each offering a reliable and standardized dose.

Tablets/Lozenges: These are designed to be swallowed or dissolved under the tongue (sublingual), which may enhance absorption.
Sprays: A convenient alternative for those who dislike tablets.
Injections: Reserved for individuals with severe deficiency or absorption issues, typically administered by a healthcare professional.

Fortified Foods

Many companies add B12 to their plant-based products, providing an easy way to get regular, smaller doses throughout the day. It is essential to read labels carefully to confirm B12 fortification and dosage.

Nutritional Yeast: A popular vegan seasoning with a nutty, cheesy flavor, often heavily fortified with B12. A tablespoon can often provide 100% of the daily value.
Plant-Based Milks: Many brands of soy, almond, and oat milk include added B12.
Breakfast Cereals: A number of breakfast cereals are fortified with B12, which can be a good way to start the day with a boost.
Vegan Meat Substitutes: Some products are enriched with B12 during production.

B12 Sources: Reliable vs. Unreliable


Feature	Reliable Plant-Based B12 Sources	Unreliable Plant-Based B12 Sources
Source	Produced by bacterial fermentation in controlled settings.	Natural growth on soil, microbial contamination, or fermentation.
Active B12	Formulated to contain bioavailable, active B12 (e.g., cyanocobalamin, methylcobalamin).	Often contains inactive B12 analogues that interfere with absorption.
Content Consistency	Standardized dose, clearly labeled on packaging.	Highly variable, depends on environmental factors and growing conditions.
Examples	Supplements, fortified plant milks, fortified cereals, nutritional yeast.	Spirulina, some seaweeds (nori), unfortified tempeh, certain mushrooms.
Recommended Intake	Health authorities endorse their use for vegans to prevent deficiency.	Should not be depended on to meet daily B12 needs due to risks.

Conclusion

Vitamin B12 is essential for nerve function, red blood cell production, and DNA synthesis. While a whole-food, plant-based diet offers immense health benefits, it cannot provide reliable B12. The source of all B12—animal or supplement—is bacteria. Therefore, the most responsible approach for vegans is to ensure consistent intake through fortified foods, supplements, or both. This allows individuals to enjoy a compassionate and healthy diet without risking serious deficiency. By focusing on reliable, man-made sources of this microbiologically produced nutrient, vegans can secure their long-term health.

For more information on vitamin B12 guidelines, consider visiting the National Institutes of Health website.(https://ods.od.nih.gov/factsheets/VitaminB12-HealthProfessional/)

Frequently Asked Questions

No, Vitamin B12 is not naturally produced by plants. While some plant products might contain trace amounts, this is often due to bacterial contamination and is not a reliable source.

Animals acquire B12 from bacteria in their environment, feed, or their own digestive systems. Humans then get B12 by consuming these animal products.

Fermented foods cannot be relied upon as a source of B12. The fermentation process can sometimes create B12, but the amount is often negligible and inconsistent, and may contain inactive analogues.

B12 analogues are chemically similar to true B12 but are biologically inactive. Consuming them can interfere with the body's absorption of active B12 and may provide false positive results on blood tests.

Vegan B12, whether in supplements or fortified foods, is created using bacterial fermentation in a controlled, sterile environment. Specific strains of bacteria are cultivated to produce the vitamin.

For most adults, the recommended dietary allowance is around 2.4 micrograms per day, though absorption is better in smaller, frequent doses. The Vegan Society recommends that all vegans use a supplement or consistently consume fortified foods to ensure adequate intake.

A B12 deficiency can lead to serious health problems over time, including anemia, nerve damage, fatigue, and cognitive issues. Since stores can last for years, deficiency often develops slowly and can go unnoticed until severe.

No. The B12 in animal products and supplements both originates from microorganisms. The B12 in fortified foods and supplements is just as bioavailable and effective for human use.