Does B12 only come from animals? The truth about its origins

December 22, 2025 •

4 min read

Specific bacteria and archaea are the true producers of vitamin B12, a nutrient that neither plants nor animals synthesize themselves. Animals acquire B12 by consuming these microorganisms, and humans then obtain it by eating animal products or through other modern sources.

Quick Summary

Vitamin B12 is produced by bacteria, not animals. While animal products contain B12 from these bacteria, fortified foods and supplements are reliable alternatives, especially for plant-based diets.

Key Points

Bacterial Origin: Vitamin B12 is produced by bacteria and archaea, not by plants or animals themselves.
Primary Animal Source: Animals absorb B12 from bacteria and store it in their tissues, making meat, dairy, and eggs common dietary sources.
Reliable Vegan Sources: The only dependable vegan options for B12 are fortified foods, such as plant milks and cereals, and supplements.
Unreliable Plant Sources: Natural plant-based foods like seaweed or tempeh contain unreliable amounts of active B12 and should not be depended upon.
Fortification is Key: Modern hygiene has reduced the amount of bacteria in our food and water, making fortification and supplementation necessary for many, particularly vegans.
Deficiency Consequences: A lack of B12 can lead to serious health issues including anemia, nerve damage, and cognitive problems.

Where Does B12 Truly Come From?

Contrary to popular belief, vitamin B12 is not naturally produced by either animals or plants, but is instead synthesized by specific microorganisms, namely certain bacteria and archaea. The reason that animal products are widely recognized as primary sources of B12 is that animals consume these bacteria and absorb the B12 they produce into their tissues, muscles, and organs. For instance, grazing animals ingest microorganisms from soil, which produce B12 in their digestive tract. As a result, humans who consume meat, eggs, and dairy products obtain their B12 indirectly from this bacterial origin. The narrative that B12 is an exclusively 'animal' nutrient is therefore a simplified, if understandable, misconception of how the nutrient enters the food chain.

Reliable Sources of Vitamin B12

To ensure adequate intake, understanding the reliable sources is key, whether you follow an omnivorous or a plant-based diet. These sources are categorized into animal-based options and modern alternatives like fortified foods and supplements.

Animal-Based Sources

These foods naturally contain vitamin B12 in varying concentrations, reflecting the animal's diet and ability to store the nutrient.

Organ Meats: Liver and kidneys are exceptionally rich sources of B12, often containing many times the daily recommended intake.
Clams and Shellfish: Small shellfish like clams and mussels are among the most concentrated natural sources of B12.
Meat and Poultry: Beef, lamb, and chicken are good sources, especially in lean cuts.
Dairy Products: Milk, yogurt, and cheese provide B12, and the bioavailability is often higher than in meat or eggs.
Eggs: The yolk of an egg is a decent source of B12.

Fortified Foods and Supplements

For vegans, vegetarians, and even many older adults who have trouble absorbing B12 from food, fortified products and supplements are a reliable way to get this nutrient.

Nutritional Yeast: Often fortified with B12, this deactivated yeast has a cheesy flavor and can be sprinkled on many dishes.
Fortified Breakfast Cereals: Many brands of cereals are fortified with B12, providing a convenient daily source.
Plant Milks: Fortified non-dairy milks like soy, almond, and oat milk are common sources.
Meat Alternatives: Some vegan meat substitutes and spreads are fortified.
Supplements: B12 supplements are widely available in various forms (pills, sprays, sublingual) and are a highly dependable option.

The Unreliable Nature of Natural Plant Sources

Some plant-based foods, such as certain seaweeds (like nori), mushrooms, and fermented products (like tempeh), may contain B12 or B12 analogues. However, these are not considered reliable sources for two main reasons. First, the B12 content is often inconsistent and can be very low. Second, many of these foods contain B12 analogues, which are chemically similar to B12 but are not biologically active in humans and can even interfere with absorption of the active vitamin. Therefore, for consistent intake, fortified foods or supplements are strongly recommended over these purported natural sources.

Deficiency Risks and Symptoms

B12 deficiency is a significant concern for several groups, including vegans, older adults, and those with gastrointestinal conditions that affect absorption, such as Crohn's disease or pernicious anemia. Because the body can store B12 for several years, deficiency symptoms can take a long time to manifest. When they do appear, they can be serious and wide-ranging, from physical to neurological and psychological symptoms. Common symptoms include fatigue, weakness, numbness or tingling in the extremities, cognitive difficulties like memory loss, and a sore or red tongue. If left untreated, severe deficiency can lead to irreversible nerve damage.

Comparison of B12 Sources


Feature	Animal Products (Meat, Dairy, Eggs)	Fortified Foods (Cereals, Plant Milks)	Supplements	Unreliable Natural Plant Sources
Natural Origin	Yes, from bacteria consumed by animals.	No, B12 is added synthetically.	No, B12 is added synthetically.	No, may contain inactive analogues.
Reliability	Highly reliable for omnivores.	Highly reliable for all, with consistent checking.	Most reliable, especially for vegans.	Unreliable, inconsistent, and often inactive.
Bioavailability	Varies by source, dairy often higher than meat.	High; crystalline form is easily absorbed.	High, especially with larger doses or sublingual forms.	Low to none; some analogues interfere with absorption.
Suitability for Vegans	Not suitable as a primary source.	Essential part of a vegan diet.	Essential part of a vegan diet.	Not recommended as a reliable source.

Conclusion

Vitamin B12 is not an exclusive product of the animal kingdom. Instead, it is a microbially produced nutrient that humans obtain from various sources. While animal products have long served as the primary source for many, modern dietary practices, including the rise of plant-based diets, have made reliable alternatives like fortified foods and supplements essential for many people. Given the serious health consequences of B12 deficiency, awareness of these sources is critical for ensuring optimal health, regardless of dietary choices. As highlighted by the National Institutes of Health, older adults and vegans, in particular, should prioritize reliable B12 sources. Ultimately, understanding where B12 truly originates empowers individuals to make informed decisions about their dietary intake and supplementation.

NIH Office of Dietary Supplements: Vitamin B12 Fact Sheet

Frequently Asked Questions

While most animal products contain vitamin B12, the amount can vary significantly based on the type of food and the animal's diet. Organ meats are much more concentrated than, for example, a serving of chicken breast.

No, it is not safe or reliable to try and obtain B12 from unwashed produce. Modern farming and sanitation practices have reduced environmental sources, and potential bacterial contamination poses other health risks.

If you don't get enough B12, you can develop a deficiency which may cause fatigue, nerve damage (tingling/numbness), megaloblastic anemia, and cognitive issues over time.

The body stores a large amount of B12 in the liver, so symptoms can take several years to appear after a person stops consuming enough of the vitamin.

The best way for a vegan to ensure adequate B12 intake is through regular consumption of fortified foods, like plant milks and nutritional yeast, and/or taking a B12 supplement.

Yes, B12 supplements are considered safe, even in larger doses, as it is a water-soluble vitamin. Any excess is typically excreted in the urine.

No, nutritional yeast does not naturally contain B12. It must be fortified with B12 during the manufacturing process to be a reliable source.

B12 levels can be checked with a blood test. However, for vegans, tests measuring methylmalonic acid (MMA) or homocysteine levels can be more reliable than a simple B12 level test.