Which B vitamin do vegetarians lack? A complete guide to B12

November 14, 2025 •

4 min read

A review of studies found a high prevalence of B12 depletion and deficiency among vegetarians, confirming that the key B vitamin vegetarians lack is B12. This is a critical nutrient for nerve function and red blood cells that is primarily found in animal products.

Quick Summary

Vegetarians are most likely to be deficient in vitamin B12, as it is found almost exclusively in animal foods. Adequate intake can be achieved through fortified products, dairy, eggs, and supplements.

Key Points

Primary Concern: Vitamin B12 is the main B vitamin lacking in vegetarian diets, particularly for vegans, as it is found naturally almost exclusively in animal products.
Essential Functions: B12 is critical for red blood cell formation, nervous system health, and DNA synthesis, so deficiency can cause serious problems.
Symptoms Can Be Subtle: B12 deficiency symptoms often appear gradually and can be non-specific, including fatigue, tingling, and mood changes, so consistent intake is crucial.
Reliable Sources: The most dependable vegetarian B12 sources are dairy, eggs, fortified foods like nutritional yeast and cereals, and supplements.
Unreliable Plants: Some plant foods like seaweed and fermented products are unreliable for B12 because they may contain inactive analogues and have inconsistent, low amounts.
Supplementation is Key: For many vegetarians, especially vegans, supplements are necessary to ensure a sufficient and consistent B12 intake.
Regular Monitoring: Periodic blood tests, including checking methylmalonic acid (MMA) levels, can help monitor B12 status and prevent severe deficiency.

Understanding the B12 challenge in a vegetarian diet

Vitamin B12, also known as cobalamin, is a crucial nutrient for numerous bodily functions. It is essential for producing red blood cells, maintaining a healthy nervous system, and aiding in DNA synthesis. A deficiency can lead to a range of health issues, including megaloblastic anemia, fatigue, nerve damage, and psychological problems. The primary challenge for vegetarians is that vitamin B12 is produced by bacteria, and in nature, the only reliable food sources are from animal products, including meat, fish, eggs, and dairy.

For many vegetarians, particularly those following a lacto-ovo diet, dairy and eggs provide some B12. However, studies show that even lacto-ovo-vegetarians can have insufficient B12 levels, and vegans, who exclude all animal products, are at a much higher risk of deficiency. The body stores B12 for several years, so deficiency symptoms may appear gradually, making consistent intake essential for long-term health.

Symptoms and risks of vitamin B12 deficiency

Recognizing the signs of a vitamin B12 deficiency is important for timely intervention. The symptoms can be subtle and develop slowly over time, so they can easily be mistaken for other issues.

Common symptoms include:

Fatigue and weakness: Feeling unusually tired or lacking energy.
Pale or yellowish skin: Due to megaloblastic anemia, where red blood cell production is impaired.
Neurological problems: Pins and needles, numbness in hands and feet, vision problems, and memory loss.
Glossitis: A sore, red, and swollen tongue.
Psychological issues: Mood swings, irritability, depression, and confusion.
Gastrointestinal issues: Diarrhea, nausea, bloating, and constipation.

If left untreated, a B12 deficiency can lead to more severe and potentially irreversible neurological damage. For pregnant and breastfeeding women, adequate B12 intake is particularly critical, as a deficiency can affect the infant's development.

Reliable sources of vitamin B12 for vegetarians

To prevent deficiency, vegetarians and especially vegans must be proactive about their B12 intake through a combination of diet and supplementation. Reliable sources include:

Dairy and eggs (for lacto-ovo vegetarians)

Eggs: Two large eggs provide a significant portion of the daily B12 requirement. The B12 in egg yolks is more easily absorbed than in egg whites.
Dairy Products: Milk, cheese, and yogurt are all good sources of B12. The B12 in dairy products is absorbed more efficiently than in meat.

Fortified foods (for all vegetarians and vegans)

Fortified Cereals: Many breakfast cereals are fortified with B12 and are a simple way to increase daily intake.
Nutritional Yeast: A deactivated yeast with a savory, cheese-like flavor, often used as a seasoning. A single tablespoon of fortified nutritional yeast can provide 100% of the daily B12 value.
Plant-Based Milks and Spreads: Look for products like soy milk, almond milk, and margarine that have been fortified with vitamin B12.

Supplements

Cyanocobalamin: This is the most common and stable form of B12 found in supplements.
Methylcobalamin: Another form, though cyanocobalamin is generally recommended due to its stability and long history of effective use.

Unreliable plant sources

Some plant-based foods, such as seaweed, certain fermented foods (like tempeh and miso), and specific mushrooms (like shiitake), are sometimes mentioned as B12 sources. However, many of these contain inactive B12 analogues that do not function in the human body and can interfere with the absorption of true B12. Their B12 content is also inconsistent and often insufficient, making them an unreliable primary source. The Vegan Society and other health organizations caution against relying on these foods.

Comparing B12 Sources for Vegetarians


Source Category	Examples	Reliability for Vegetarians	Notes
Animal Products (Dairy & Eggs)	Milk, cheese, yogurt, eggs	Good (for lacto-ovo only)	Bioavailability varies; often not sufficient alone for high-risk individuals.
Fortified Foods	Breakfast cereals, nutritional yeast, plant milks	High	A very reliable and accessible source, especially for vegans.
Supplements	Tablets, sublingual, injections	Very High	Direct and dependable source for ensuring adequate intake.
Some Plant-Based Items	Seaweed, mushrooms, fermented products	Low / Inconsistent	Often contain inactive B12 analogues that can interfere with absorption.

The importance of testing and supplementation

Given the risk of deficiency, especially for those on long-term plant-based diets, regular monitoring of B12 levels is recommended. Blood tests for serum B12 are the standard, but checking for levels of methylmalonic acid (MMA) is a more sensitive indicator of functional B12 status. An elevated MMA level indicates that the body's B12 stores are being depleted.

For those who do not regularly consume dairy, eggs, or fortified foods, supplementation is the most effective and reliable strategy to prevent deficiency. Many health professionals recommend supplements for all vegans and often for long-term vegetarians as well.

Conclusion: Strategic intake is vital

For vegetarians, the primary B vitamin of concern is B12, due to its limited natural availability in plant foods. While lacto-ovo vegetarians can derive some B12 from dairy and eggs, reliance on fortified foods and, for many, supplementation is a necessary and prudent strategy to avoid deficiency. By understanding the sources, recognizing the symptoms, and incorporating reliable strategies like fortified foods and supplements, vegetarians can ensure they maintain healthy vitamin B12 levels and prevent potential long-term health complications. Consult a healthcare professional to determine the right approach and dosage for your needs.

For more detailed information on vitamin B12, including dietary reference values, consult the National Institutes of Health (NIH) Office of Dietary Supplements website: Vitamin B12 - Health Professional Fact Sheet

Frequently Asked Questions

Vitamin B12 is produced by microorganisms, not plants. Animals obtain B12 from bacteria in their environment or diet, and it is then stored in their tissues and products, making animal-sourced foods the primary natural source.

The initial symptoms are often non-specific and can include fatigue, a lack of energy, and weakness. Over time, more distinct signs like a sore tongue, numbness or tingling, and memory problems may develop.

While dairy and eggs contain B12 and can be important sources for lacto-ovo-vegetarians, they may not provide a sufficient amount for everyone. Many vegetarians, and especially vegans, need to rely on fortified foods or supplements to meet their needs.

Good sources include fortified nutritional yeast, breakfast cereals, and plant-based milks and spreads that have been enriched with B12. It is important to always check the product label to confirm it contains added B12.

The most reliable sources for vegans are fortified foods and dietary supplements. Nutritional yeast and fortified plant milks are good dietary options, but supplements are a very dependable method for ensuring adequate intake.

Yes, research shows that the body absorbs small amounts of B12 more efficiently than large, infrequent doses. Taking smaller doses more often, possibly split with meals, can optimize absorption.

Untreated B12 deficiency can lead to severe and potentially irreversible health issues. These can include persistent nerve damage, heart conditions, and a decline in cognitive functions like memory and judgment.