Is there any plant source of vitamin B12?

December 12, 2025 •

4 min read

Vitamin B12 is essential for neurological function, red blood cell formation, and DNA synthesis, yet it is synthesized only by microorganisms and not by plants. Consequently, naturally occurring, reliable plant sources of active B12 are extremely limited, posing a challenge for those on a strict vegan diet.

Quick Summary

The search for plant-based vitamin B12 reveals that plants do not naturally produce this nutrient. Bioactive B12 is found in some fortified foods and potentially certain algae and fungi, but their reliability varies. A deep dive into the evidence clarifies how vegans and vegetarians can meet their B12 needs safely and effectively.

Key Points

Bacteria are the source: Vitamin B12 is synthesized by microorganisms, not by plants, and enters the food chain through animal products or bacterial interaction.
Unreliable plant sources: Foods like spirulina, most nori, and some fermented products are unreliable for B12 due to inconsistent levels or the presence of inactive analogues.
Fortified foods are key: The most dependable way for vegans to get B12 is by regularly consuming fortified foods like nutritional yeast, cereals, and plant-based milks.
Supplements offer consistency: For a consistent and guaranteed intake, a B12 supplement is the most reliable option for vegans and other at-risk individuals.
Deficiency risks are serious: Untreated B12 deficiency can lead to severe health problems, including irreversible nerve damage, and can be masked by high folate intake common in plant-based diets.

The Truth Behind Vitamin B12 and Plants

Where Vitamin B12 Actually Comes From

Vitamin B12, or cobalamin, is crucial for human health, playing a key role in numerous metabolic processes. Unlike other vitamins, it is exclusively produced by bacteria and archaea, not by plants or animals themselves. Animals acquire B12 through symbiotic bacteria in their digestive systems or by consuming bacteria-laden foods, which is why meat, dairy, and eggs are traditional sources of this nutrient. Plant-based diets, therefore, lack reliable natural B12 sources, making supplementation or fortification necessary for vegans and, in some cases, vegetarians.

The Misconception of Natural Plant B12 Sources

For years, some plant foods have been wrongly touted as natural sources of vitamin B12. Many studies have debunked these claims, showing that any B12 detected in these foods is either inactive (analogues) or the result of bacterial contamination.

Spirulina and Blue-Green Algae: These popular supplements are a prime example. While early tests suggested the presence of B12, further analysis revealed the compound was a pseudovitamin, or B12 analogue, that is biologically inactive in humans. Relying on these sources can be dangerous, as the analogues can interfere with the absorption of true B12.
Nori and Seaweed: While some studies, particularly from Japan and Korea, have found active B12 in dried purple laver (nori), the content can vary widely depending on the growing environment and microbial interaction. The Vegan Society and other health organizations advise against relying on seaweed alone due to this inconsistency.
Mushrooms: Certain mushrooms, like shiitake, may contain trace amounts of B12 due to bacteria in the soil or growing medium. However, the levels are generally too low and unreliable to satisfy daily requirements.
Fermented Foods: Foods like tempeh and some kimchis have shown inconsistent B12 levels. This is typically due to bacterial contamination during processing, not a natural property of the food itself. In Western countries with standardized food production, B12 contamination is much less common and fermented plant foods are not considered reliable sources.

Reliable Plant-Based Sources: The Role of Fortification and Supplements

For those on a plant-based diet, the most dependable way to get vitamin B12 is through fortified foods and supplements. These sources use cyanocobalamin, a stable and well-absorbed form of the vitamin.

Fortified Breakfast Cereals: Many cereals are fortified to contain a significant percentage of the daily B12 requirement. Always check the nutrition label to confirm fortification levels.
Nutritional Yeast: This popular vegan condiment is often heavily fortified with vitamin B12. Just a tablespoon can provide a full day's worth of B12. Look for brands that explicitly state they are B12-fortified.
Fortified Plant Milks: Soy, almond, and oat milks frequently have added B12, making them a convenient daily source. As with cereals, checking the label is essential.
Supplements: For consistent intake, especially for individuals with poor absorption, a B12 supplement is the most reliable option. Doses can range from a daily low-dose supplement to a weekly high-dose one.

Comparing Natural vs. Fortified B12 for Vegans


Feature	Naturally Occurring (in some plants/algae)	Fortified Foods & Supplements
Reliability	Unreliable due to varying content and presence of inactive analogues.	Very reliable and consistent source of active B12.
Form of B12	Often contains a mix of active B12 and inactive analogues (pseudovitamin B12).	Typically contains cyanocobalamin, a stable and bioavailable form.
Bioavailability	Inconsistent; some analogues may interfere with absorption.	High absorption rate, especially in small, frequent doses.
Convenience	Can be difficult to find and requires careful sourcing and preparation.	Readily available and easy to incorporate into a daily routine.
Risk Factor	Potential risk of deficiency if relied upon as a sole source.	Minimal risk when directions are followed; prevents deficiency effectively.

The Health Risks of B12 Deficiency

Vitamin B12 deficiency can lead to serious health issues if left untreated. For vegans, particularly those who have been unsupplemented for many years, the risk is significant. Symptoms can include:

Megaloblastic anemia
Nerve damage (peripheral neuropathy)
Fatigue and weakness
Cognitive issues, memory loss, and confusion
Depression

Since vegan diets are often rich in folate, a B-vitamin that can mask the anemia caused by B12 deficiency, the neurological damage can advance undetected. This makes regular monitoring and proactive supplementation crucial for all vegans and vegetarians.

Conclusion: How to Get Your B12 on a Plant-Based Diet

While the concept of natural plant-based vitamin B12 is appealing, the scientific consensus is clear: plants do not produce active, bioavailable B12. Any trace amounts found in certain plants, algae, or fermented foods are too unreliable to prevent deficiency. The most effective and safest strategy for anyone on a vegan or plant-focused diet is to regularly consume fortified foods, such as nutritional yeast, breakfast cereals, and plant-based milks, or to take a reliable B12 supplement. By understanding the science and taking proactive steps, vegans and vegetarians can ensure they meet their nutritional needs and maintain optimal health. For further reading, consult the Vegan Health website for a detailed overview of B12 in plant foods.

Frequently Asked Questions

No, plants do not produce vitamin B12. Any trace amounts found in some plant-derived foods are either inactive analogues or the result of bacterial contamination, making them an unreliable source for meeting daily requirements.

Fermented foods like tempeh are not a reliable source of active B12, especially in Western countries. While some batches might show traces due to bacterial contamination, the amount is inconsistent and insufficient to rely on for your daily intake.

Nutritional yeast is a reliable vegan source of B12 because it is fortified, meaning the active vitamin is added during processing. Always check the product label to ensure it has been fortified with cyanocobalamin.

A B12 analogue is a compound that is chemically similar to active B12 but is biologically inactive in humans. Relying on foods containing these analogues, like spirulina, is problematic because they do not prevent deficiency and can even interfere with the body's absorption of active B12.

Vitamin B12 deficiency can occur within the first two years of starting a plant-based diet, though it may take longer. Since the body stores some B12, early symptoms might not appear immediately, but ongoing deficiency can lead to serious health issues.

The most effective ways for vegans to get B12 are by consuming fortified foods like plant-based milks, cereals, and nutritional yeast, or by taking a regular B12 supplement.

Yes, vegetarians are also at risk for B12 deficiency, though less so than vegans, because they often consume some B12 from dairy and eggs. However, fortified foods and supplements are still recommended for consistent intake, as deficiency is common among vegetarians.