Does B12 Come from Dirt? The Myth and the Modern Reality

November 16, 2025 •

4 min read

According to a study published in Nature, less than 10% of soil bacteria and archaea possess the genetic potential for B12 synthesis, and even when present, modern sanitation makes it unreliable. This reveals that while the claim that 'does B12 come from dirt' has a scientific root, relying on it for modern nutrition is ill-advised.

Quick Summary

Explore the bacterial origins of Vitamin B12 and why contemporary food systems make dirt an unreliable source. Understand how humans obtain cobalamin and the importance of supplementation for specific diets.

Key Points

Bacterial Origin: Vitamin B12 is not made by plants or animals, but by specific bacteria and archaea found in soil and water.
Unreliable Soil Source: Modern sanitation and agricultural methods, including pesticides, have made relying on incidental exposure to soil bacteria an unsafe and unreliable way to obtain B12.
Animal-Based Transfer: Herbivores get B12 from gut bacteria or supplemented feed, and humans get it by consuming animal products like meat, dairy, and eggs.
Supplementation is Key: Vegans, vegetarians, and older adults are at higher risk for deficiency and should rely on fortified foods or supplements for a consistent and reliable B12 source.
Bioavailability Varies: B12 in supplements (crystalline form) and fortified foods is often more easily absorbed than the protein-bound B12 found naturally in animal products.
Modern Production: The B12 in commercial supplements and fortified foods is produced via industrial-scale bacterial fermentation.

The Bacterial Origin of Vitamin B12

Contrary to popular belief, neither plants nor animals produce vitamin B12; it is synthesized exclusively by specific bacteria and archaea. These microorganisms are naturally present in environments like soil and water. The vitamin, also known as cobalamin, is vital for humans, playing a crucial role in red blood cell formation, neurological function, and DNA synthesis. The complex chemical structure of B12, centered around a cobalt atom, gives it its unique properties. For centuries, humans and other animals likely acquired B12 through incidental contact with soil bacteria, for example, by eating unwashed produce or drinking untreated water. However, modern hygiene and agricultural practices have drastically changed this relationship.

The Modern Disconnect from Soil B12

Today's food system is built on cleanliness and efficiency, which has a significant impact on our exposure to beneficial bacteria. Fruits and vegetables are thoroughly washed, sanitized, and treated with pesticides, which largely eliminates any trace of B12-producing microbes. As a result, plant-based foods, unless fortified, are not reliable sources of active B12 for humans. Moreover, industrial farming practices have depleted soil nutrients and changed the diet and living conditions for livestock. Animals raised indoors often have minimal contact with soil and are fed concentrated grain diets. To ensure their B12 levels, and subsequently the B12 content in meat and dairy, artificial B12 is often added to their feed.

How the Food Chain Transfers B12 to Humans

Since humans cannot produce B12 internally (though some gut bacteria do, it's produced too far down the digestive tract for absorption), we must obtain it through our diet. The transfer happens primarily through animal-derived foods.

Ruminant Animals: Grazing animals like cows and sheep have a unique digestive system with a rumen, a specialized stomach chamber. Here, B12-synthesizing bacteria thrive, and the B12 they produce is absorbed by the animal and stored in its tissues and milk.
Fish and Shellfish: In marine ecosystems, B12-producing bacteria are consumed by phytoplankton, which in turn are eaten by zooplankton and fish. This process concentrates B12 up the food chain, making fish and shellfish excellent sources.
Eggs and Poultry: Omnivores like chickens and pigs also obtain B12 from their feed, which may include insects or supplemented grain. This B12 is then stored in their meat and eggs.

Reliable Modern Sources of B12

Given the unreliability of soil as a direct source, modern diets depend on alternative methods for B12 intake. The main reliable options are animal products, fortified foods, and supplements.

Animal-Based Foods: These remain a natural source of B12 for omnivores. High-concentration sources include liver, kidneys, clams, and other organ meats, but significant amounts are also found in milk, cheese, and eggs.
Fortified Foods: Many modern plant-based products, like cereals, nutritional yeast, and non-dairy milks, are fortified with a crystalline form of B12. This form is often more easily absorbed by the body than the protein-bound B12 in animal products, especially for older adults.
B12 Supplements: The B12 used in supplements and fortified foods is produced on an industrial scale through bacterial fermentation. This ensures a consistent, high-quality, and bioavailable dose for those who need it, especially vegans and vegetarians.

Comparison of B12 Sources for a Balanced Diet


Source	B12 Origin	Reliability for Humans	Absorption for Humans	Typical Diet	Best For	Notes
Animal Products	Bacteria from animal gut/feed	Very Reliable	Can be complex for some	Omnivore/Carnivore	General population	B12 is protein-bound, absorption can be impaired in some individuals.
Fortified Foods	Industrial bacterial fermentation	Very Reliable	Often better absorption	Vegan, Vegetarian, Omnivore	Everyone, especially those over 50	Crystalline B12 is not protein-bound, making it easier to absorb.
Supplements	Industrial bacterial fermentation	Very Reliable	Excellent absorption	Vegan, Vegetarian, Omnivore	Vegans, older adults, malabsorption issues	Offers precise dosing and is highly bioavailable.
Mushrooms/Algae	Concomitant bacteria in cultivation	Not Always Reliable	Varies, sometimes inactive analogues	Vegan, Vegetarian	Only certain species	Some algae like nori contain active B12, but amounts can be inconsistent.
Soil/Unwashed Produce	Wild soil bacteria	Extremely Unreliable	Minimal to none	None (not recommended)	None	Modern sanitation and agriculture make this unsafe and unreliable.

Conclusion: The Source of Your B12

While the concept of getting vitamin B12 from dirt has a fascinating basis in natural microbial processes, it is a practice rendered obsolete and unsafe by modern life. The foundation of B12 remains with certain bacteria, but the delivery mechanism has fundamentally shifted. For herbivores, it's their symbiotic gut flora. For omnivores, it's the animal products they consume. And for vegans, or anyone with compromised absorption, it's fortified foods and pharmaceutical-grade supplements derived from controlled bacterial fermentation. Understanding the true origin of B12 and its modern distribution ensures everyone can maintain adequate levels of this critical nutrient without resorting to outdated and unhygienic practices. It is a testament to both nature's ingenuity and scientific progress that we can source this vital compound reliably and safely in the 21st century.

A Final Word on Optimal B12 Intake

For optimal health, it's recommended that vegans and vegetarians use B12 fortified foods or a certified supplement. Annual check-ups to monitor your B12 status are also recommended, especially for vulnerable populations like pregnant women, older adults, and those with specific health conditions. Supplements are a safe and effective method to meet daily requirements, and the crystalline form used is highly absorbable. The best approach is to follow dietary guidelines from reputable health organizations and seek professional advice when needed, ensuring your intake is consistent and sufficient. National Institutes of Health Fact Sheet on B12

Frequently Asked Questions

No, it is not safe or reliable to obtain B12 this way. While bacteria in soil produce B12, the presence is inconsistent and the risk of ingesting harmful pathogens from unwashed produce is very high due to modern farming and hygiene practices.

Animals obtain B12 in different ways. Ruminants like cows and sheep have symbiotic bacteria in their stomachs that produce B12. Other livestock often have B12 supplements added to their feed, especially in modern farming.

The most reliable sources for vegans are B12 fortified foods, such as certain plant milks, nutritional yeast, and cereals, or taking a regular B12 supplement.

The B12 used in fortifications and supplements is produced by bacteria in a lab setting and is chemically identical to natural B12. It is often more bioavailable because it is not protein-bound, aiding absorption.

B12 deficiency is common in the general population, especially older adults, due to malabsorption issues. The body's ability to absorb the protein-bound B12 from animal foods can decline with age or due to health conditions affecting the digestive system.

Most omnivores get sufficient B12 from animal products. However, some groups, particularly adults over 50 and those with absorption disorders, may still benefit from supplements, as they can more easily absorb the crystalline B12.

Many fermented foods and some mushrooms and algae contain trace amounts of B12, but often in the form of inactive analogues that the human body cannot use effectively. They are not considered reliable sources for meeting daily requirements.