Where did vitamin B12 come from? A deep dive into its microbial origins

Less than 10% of the B12 in eggs is bioavailable to the human body, a surprising fact given their reputation as a B12 source. But to truly understand B12, we must look at its remarkable journey, and answer the question: where did vitamin B12 come from in the first place? The surprising answer lies not in animals or plants, but in the microscopic world of bacteria and archaea.

Quick Summary

Vitamin B12 is synthesized exclusively by certain bacteria and archaea, and is not produced by plants or animals. Humans and other animals acquire this essential nutrient either directly or indirectly by consuming animal products where it has been stored, or through fortified foods and supplements produced via microbial fermentation.

Key Points

• Microbial Origin: Vitamin B12 is produced exclusively by certain bacteria and archaea, not by plants or animals.

• Animal Storage: Animals acquire B12 by consuming these microorganisms and store it in their tissues, which is why animal products are a source for humans.

• Industrial Fermentation: The B12 in supplements and fortified foods is produced on an industrial scale using microbial fermentation in large vats.

• Synthetic vs. Natural: Synthetic B12 (cyanocobalamin) is highly stable and used in many products, while natural B12 (methylcobalamin) is found in foods. Both are effective once converted by the body.

• Plant-Based Sources: Reliable plant-based sources are limited to fortified foods and supplements, as the B12 in certain algae or mushrooms is inconsistent or bound up by symbiotic bacteria.

• Absorption: Absorption varies by source; B12 in supplements is often easier to absorb, especially for those with digestive issues, as it is in a free form.

The Unseen Producers: Bacteria and Archaea

Unlike most vitamins, which can be synthesized by plants or animals, vitamin B12 (also known as cobalamin) is only produced by specific bacteria and archaea. This makes it a unique and crucial compound in biological systems, and means that its presence in our food supply is the result of intricate biological processes and food chains. In nature, these microorganisms live in various environments, including soil, aquatic ecosystems, and the digestive tracts of animals.

The Role in Animal Food Sources

The presence of vitamin B12 in animal products is a secondary acquisition, not a result of the animal's own synthesis. Animals consume the B12-producing microorganisms present in their food and environment, and the vitamin is then absorbed and stored in their tissues.

• Ruminants (e.g., cattle and sheep): Herbivores like cows and sheep have a unique digestive system with a rumen, a specialized stomach compartment rich in B12-synthesizing bacteria. These animals can absorb the B12 produced by these symbiotic bacteria, and it accumulates in their meat and milk.
• Other Animals: Omnivores like chickens and fish also acquire B12 through their diet. For example, fish consume phytoplankton and other organisms that have, in turn, acquired B12 from bacteria in aquatic food chains.
• Historical Context: In the past, less hygienic food production practices meant that humans may have acquired some B12 from soil residue on unwashed produce. However, modern sanitation has made this an unreliable source.

The Journey to Fortified Foods and Supplements

The discovery that only microorganisms produce B12 revolutionized how we manage nutritional deficiencies. This knowledge was especially vital for addressing pernicious anemia, which is caused by B12 deficiency. The solution was to harness the power of microbes on an industrial scale.

Microbial Fermentation

Today, the B12 used in supplements and fortified foods is produced through a large-scale microbial fermentation process. Large vats are filled with specific, high-yield strains of bacteria, such as Propionibacterium freudenreichii or Ensifer adhaerens, that are fed a nutrient-rich medium. After fermentation, the B12 (in a raw form) is extracted, purified, and converted into a stable form, typically cyanocobalamin, for commercial use. This ensures a consistent and reliable supply for people who need it, especially vegans and vegetarians.

The Production Process:

1. Selection of Microorganism: Strains like Propionibacterium freudenreichii are chosen for their high B12-producing efficiency.
2. Fermentation: The microbes are cultured in huge vats for several days, converting the raw materials into B12.
3. Extraction: The B12 is recovered from the bacterial culture, sometimes by lysing the cells with heat.
4. Purification: Multiple steps, including chromatography and crystallization, are used to purify the B12.
5. Conversion: The final product is often converted to cyanocobalamin for stability and cost-effectiveness.

Natural vs. Synthetic Vitamin B12

There are key differences between B12 found in animal products and the synthetic form used in fortified foods and supplements.

Feature	Naturally-Sourced B12 (from animal products)	Synthetically-Sourced B12 (from supplements/fortified foods)
Origin	Created by bacteria consumed by animals, which then store it in their tissues.	Produced by specific, cultivated bacteria in a controlled fermentation process.
Form	Primarily exists as methylcobalamin and adenosylcobalamin, its active coenzyme forms.	Most commonly found as cyanocobalamin, a highly stable, manufactured form.
Absorption	Protein-bound B12 requires separation by stomach acid and enzymes before absorption, which can be less efficient.	Already in a free, crystalline form, potentially making absorption easier for some individuals, particularly those with low stomach acid.
Bioavailability	Variable, and can be relatively low depending on the food source and a person's digestive health.	Often higher, with a steady absorption rate. However, larger doses have diminishing returns.
Cost	Dependent on the cost of animal farming and processing.	Generally more cost-effective to produce on a large scale.

Plant-Based Sources: A Deeper Look

Since plants do not naturally produce B12, sources for vegans and vegetarians are limited and often misunderstood. While some plant-based foods contain B12-like compounds, many are inactive or pseudovitamin B12. Reliable vegan sources rely on bacterial interaction or fortification.

• Fortified Foods: The most reliable vegan sources are foods fortified with B12, such as nutritional yeast, plant-based milks, and breakfast cereals.
• Algae and Mushrooms: Some species, like nori seaweed and certain mushrooms, contain active B12. However, the levels can be inconsistent and may not be sufficient for daily needs, making supplementation a safer choice. The B12 in these foods is actually derived from symbiotic bacteria.
• Supplements: For those following a strict plant-based diet, supplements containing cyanocobalamin or methylcobalamin are the most dependable way to ensure adequate B12 intake.

Conclusion: A Global Nutrient from Microscopic Life

The story of where vitamin B12 came from is a fascinating tale of microbiology and human ingenuity. It highlights the essential role that bacteria and archaea play in our global ecosystem, acting as the sole biological manufacturers of this critical nutrient. We get B12 either indirectly by consuming animal products, which have accumulated the vitamin from microorganisms, or directly from supplements and fortified foods created through industrial fermentation. This understanding is crucial for ensuring everyone, regardless of their dietary choices, can maintain proper B12 levels and avoid the serious health consequences of a deficiency.

References

• Fang, H., Kang, J., Zhang, D. (2017). Vitamin B12 sources and microbial interaction. Nutrients, 9(4), 312.
• Fang, H., Kang, J., Zhang, D. (2017). Vitamin B12 sources and microbial interaction. PMC.
• Forks Over Knives. (2017). Vitamin B12: All Your Questions Answered.
• Healthline. (2024). Vitamin B12 Foods: 12 Great Sources.
• Quadram Institute. (2023). An environmentally friendly vitamin B12 production method.
• Office of Dietary Supplements. (2025). Vitamin B12 - Health Professional Fact Sheet. NIH.
• WebMD. (2024). What Are Plant Food Sources of Vitamin B12?.

Frequently Asked Questions

Which specific microorganisms produce vitamin B12?

A variety of bacteria and archaea synthesize vitamin B12, including strains of Pseudomonas denitrificans, Propionibacterium freudenreichii, and Bacillus megaterium. These microbes are used in the commercial fermentation processes that produce B12 for supplements and fortified foods.

How do animals get vitamin B12 if they can't produce it?

Animals acquire vitamin B12 by consuming the microorganisms that produce it. Herbivores like cattle absorb B12 from bacteria in their digestive systems, while fish obtain it through the food chain from plankton and other marine life that have a symbiotic relationship with B12-producing bacteria.

Can humans get B12 directly from soil or plants?

For most people today, consuming unwashed produce is not a reliable way to get vitamin B12. While some plants have traces of B12 due to bacterial interaction, their levels are inconsistent and generally insufficient for human needs. Modern hygiene practices also remove much of the soil bacteria that might contain B12.

What is the difference between cyanocobalamin and methylcobalamin?

Cyanocobalamin is a synthetic, stable form of B12 often used in supplements and fortified foods. Methylcobalamin is a natural, active form of B12 found in animal products. The body can convert cyanocobalamin into the active forms it needs.

Why is B12 from fortified foods often better absorbed?

The B12 in fortified foods and supplements is in a free, crystalline form, which doesn't require the same digestive steps as the protein-bound B12 in animal products. This can result in more efficient absorption, especially for older adults who may have lower stomach acid.

Are there reliable vegan food sources of B12?

The most reliable vegan sources of B12 are fortified foods, such as nutritional yeast, some cereals, and plant-based milks, along with dietary supplements. Other potential sources like certain algae and mushrooms can have variable and unreliable B12 content.

How is the synthetic B12 in supplements made?

Synthetic B12 is produced by feeding specific bacteria or archaea a nutrient-rich medium in large fermentation tanks. After fermentation, the resulting cobalamin is extracted, purified, and treated with cyanide to form the stable cyanocobalamin used in supplements and fortification.