Is There B12 in Grass? Understanding Herbivores and Vitamin Synthesis

December 6, 2025 •

2 min read

A 2024 review in the journal Nutrients highlighted the critical role of soil microbes in the global cobalamin cycle, the source of vitamin B12. The simple answer to "is there B12 in grass" is no; plants do not produce this vitamin, yet grazing animals naturally obtain it through a sophisticated biological process involving cobalt and bacteria.

Quick Summary

Vitamin B12 is produced by bacteria, not plants like grass. Herbivores, particularly ruminants, get their B12 by consuming cobalt, a mineral that allows stomach bacteria to synthesize the vitamin. Modern agriculture and soil health influence this process, affecting both livestock and human nutrition.

Key Points

Bacteria, not grass, make B12: Vitamin B12 is produced exclusively by certain bacteria and archaea, not by plants like grass.
Ruminants rely on gut microbes and cobalt: Grazing animals like cows and sheep get B12 from bacteria in their rumen that synthesize the vitamin from cobalt found in the soil.
Modern farming affects B12: Intensive farming and soil depletion often lead to cobalt deficiencies, requiring farmers to supplement livestock feed with cobalt or give direct B12 injections.
Human B12 comes from animal products or supplements: Humans obtain B12 by consuming animal products like meat and dairy, or through fortified foods and supplements made via bacterial fermentation.
Vegan B12 comes from fortified foods and supplements: Plant-based sources like unfortified seaweed or nutritional yeast are not reliable sources of active B12; fortified foods and supplements are necessary for vegans.
Soil microbes are the ultimate source: Whether through animals or supplements, the original source of all dietary B12 is the synthesizing activity of microorganisms.

The Surprising Source of Vitamin B12 in a Herbivore's Diet

For many, the idea that herbivores get their B12 directly from grass is a common misconception. The reality is more complex and depends entirely on a microbial relationship. While vitamin B12 is essential for all mammals, including humans and cows, neither plants nor animals can produce it on their own. The source is almost always microorganisms, specifically certain bacteria and archaea found in soil and water.

How Ruminants Make Their Own B12

Animals like cattle, sheep, and goats are called ruminants because they have a unique four-chambered stomach. The first chamber, the rumen, is a fermentation vat teeming with B12-producing bacteria. Grazing ruminants consume grass and small amounts of soil. The grass provides no B12, but the soil contains cobalt. In the rumen, symbiotic bacteria use cobalt to synthesize vitamin B12. The B12 is absorbed later in the digestive tract and stored in tissues like the liver. This makes grazing ruminants a source of B12 for humans who consume their products. Modern farming can impact this process, often requiring farmers to provide cobalt supplements or B12 injections.

Other Herbivores and B12 Acquisition

Non-ruminant herbivores like rabbits may practice cecotrophy to obtain B12 from gut bacteria. Wild herbivores may ingest soil during foraging.

Plant vs. Animal-Derived B12 Sources

Some plant-based foods may contain trace B12 from bacterial activity but are generally not reliable sources. Inactive B12 analogues can also interfere with metabolism.


Feature	B12 from Animal Sources	B12 from Plant Sources	Note
Production Source	Synthesized by gut bacteria in animals from cobalt.	Fortified foods or supplements via industrial bacterial fermentation.	Most natural B12 originates from microbes.
Reliability	Generally a reliable dietary source of absorbable B12 for omnivores.	Unreliable in nature; must rely on fortified foods or supplements.	High-quality organic sources are best, but supplements are the most reliable source for vegans.
Nutrient Transfer	Stored in animal tissue and milk, passed to human consumers.	Not inherently present in plants; requires fortification or supplements.	The pathway is indirect for both options.
Absorption Rate	Absorption from dairy and meat is generally efficient for non-compromised digestive systems.	Absorption rates can vary, but fortified sources can be highly effective.	Absorption can decrease with age or certain conditions, regardless of source.

Conclusion

Grass does not contain vitamin B12. Herbivores obtain B12 from microorganisms in their digestive system, which require cobalt, often found in soil. Humans primarily get B12 from animal products, fortified foods, or supplements, originating from either natural processes or industrial bacterial fermentation. For vegans, fortified foods and supplements are essential. The source of B12 for livestock and the nutritional quality of our food are connected to soil microbes {Link: Facebook https://www.facebook.com/RipEsselstyn/posts/people-love-to-bring-up-b12-like-its-a-reason-to-eat-meatbut-heres-the-irony-eve/1319247703198806/}.

Authoritative Resource on B12

For more in-depth scientific information on vitamin B12 metabolism and sources, a great resource is the fact sheet from the National Institutes of Health (NIH): Vitamin B12 - Health Professional Fact Sheet

Frequently Asked Questions

Cows, being ruminants, have B12-producing bacteria in their stomachs. They ingest the mineral cobalt from the soil and grass, which these bacteria use to synthesize the vitamin B12 that the cow's body can absorb.

Relying on unwashed vegetables is not a safe or reliable way to get enough B12. While soil bacteria produce B12, modern agricultural and cleaning practices make it impractical, and contamination risks are high.

The active forms of B12 are chemically the same. The difference is the source: B12 from a cow comes from gut microbes, while supplemental B12 is mass-produced using bacterial fermentation in a controlled, industrial environment.

Fortified foods like cereals, plant-based milks, and nutritional yeast have B12 added during manufacturing. The B12 used for fortification is produced by bacteria in a lab, making it a controlled and reliable source.

Wild herbivores also rely on gut bacteria and environmental cobalt. Historically, humans and animals consumed soil with their food, acquiring B12 naturally. However, modern agriculture alters this natural process for livestock.

Cobalt is an essential mineral that is the central component of the vitamin B12 molecule. B12-producing bacteria require sufficient cobalt in the environment to synthesize the vitamin.

The B12-producing bacteria in the human large intestine (colon) are located too far down the digestive tract for efficient absorption. Absorption primarily occurs in the small intestine, well before the colon.