Which vitamin is deficient in vegetarians? An Essential Guide to B12 and More

October 25, 2025 •

5 min read

Studies consistently show that vegetarians and vegans are at a higher risk of developing a vitamin B12 deficiency due to the natural absence of this nutrient in plant-based foods. Therefore, understanding which vitamin is deficient in vegetarians is the first step toward safeguarding your health on a plant-based diet.

Quick Summary

Vitamin B12 is the primary nutrient of concern for vegetarians and vegans, as it is found naturally almost exclusively in animal products. This guide details the crucial roles of vitamin B12, deficiency symptoms, and provides reliable sourcing strategies through fortified foods and supplements to ensure adequate intake and prevent serious health complications.

Key Points

Primary Deficiency: The most significant vitamin deficiency concern for vegetarians, especially vegans, is vitamin B12, as it is primarily found in animal products.
Why It’s Lacking: Plants do not naturally produce vitamin B12; production is limited to microorganisms, making fortified foods and supplements crucial for intake.
Diverse Sources: Lacto-ovo-vegetarians can get some B12 from dairy and eggs, while fortified cereals, nutritional yeast, and supplements are essential for all vegetarians.
Monitor Other Nutrients: Vegetarians should also be mindful of potential shortfalls in iron, omega-3 fatty acids, vitamin D, and zinc, and plan accordingly.
Check for Symptoms: Watch for symptoms of B12 deficiency such as fatigue, nerve issues, and changes in mood or memory, and consult a doctor if concerned.
Proactive Planning: Regular monitoring and incorporating a combination of diet, fortified foods, and supplements are the most reliable methods for maintaining optimal nutrient levels.

The Primary Nutrient of Concern: Vitamin B12

For anyone following a vegetarian or vegan diet, vitamin B12 is the nutrient that requires the most vigilant attention. This water-soluble vitamin plays a critical role in some of the body's most essential functions, and without a deliberate strategy for intake, deficiency is a significant risk. Because the human body can store a several-year supply of B12 in the liver, symptoms may take a long time to emerge, leading to a false sense of security. However, once reserves are depleted, the health consequences can be severe and, in some cases, irreversible.

Why Vitamin B12 is Absent from Plant Foods

The reason for this nutritional gap is fundamentally biological. Vitamin B12 is produced by microorganisms, not by plants. As a result, it is found naturally and reliably only in animal-based foods, such as meat, fish, eggs, and dairy. While some plant-based foods, like certain algae or fermented products, may contain inactive forms of B12 or traces due to contamination, these are not reliable or sufficient sources. For this reason, a carefully planned approach to supplementation or fortification is essential for those on plant-based diets.

Critical Roles of Vitamin B12 in the Body

Vitamin B12 is indispensable for several vital bodily processes:

Red Blood Cell Formation: It is essential for the production of healthy red blood cells. A deficiency can lead to megaloblastic anemia, a condition where red blood cells are abnormally large and unable to function correctly.
Nervous System Function: B12 is crucial for maintaining the health of nerve cells and the proper functioning of the central nervous system. Prolonged deficiency can cause nerve damage, tingling sensations, numbness, and issues with balance and coordination.
DNA Synthesis: It is a key cofactor in the synthesis of DNA, the genetic material in all cells.
Cognitive Function: Adequate B12 levels are linked to normal brain function, memory, and mood regulation. Deficiency can lead to confusion, memory loss, and even dementia-like symptoms.

Addressing Deficiency: Reliable Sources for Vegetarians

Depending on the specific type of vegetarian diet, the approach to ensuring adequate B12 intake will differ. For most, this involves a combination of fortified foods and supplements.

Sources of Vitamin B12 for Vegetarians

Eggs and Dairy Products: Lacto-ovo-vegetarians can get B12 from eggs, milk, cheese, and yogurt. However, the amount from these sources can be low, and reliance on them alone may not be sufficient for everyone.
Fortified Foods: These are a reliable and common source of B12 for both vegetarians and vegans. Many breakfast cereals, nutritional yeasts, soy and plant-based milks, and meat alternatives are fortified with the vitamin. It is crucial to check the product labels to ensure B12 has been added.
Supplements: For many, especially vegans and older vegetarians, a supplement is the most reliable way to meet daily B12 needs. These come in various forms, including tablets, sprays, and injections.

Other Potential Nutrient Shortfalls to Consider

While B12 is the most prominent concern, other nutrients can also be limited on a plant-based diet.

Iron: The iron found in plant foods (non-heme iron) is less easily absorbed than the iron in meat (heme iron). To boost absorption, consume iron-rich plant foods like lentils, beans, and spinach alongside a source of vitamin C.
Omega-3 Fatty Acids: Long-chain omega-3s, EPA and DHA, are most readily available from fatty fish. Plant-based sources like flaxseeds, chia seeds, and walnuts provide ALA, but the conversion to EPA and DHA in the body is inefficient. Algal oil supplements are an excellent vegan source of DHA and EPA.
Vitamin D: While sunlight is a primary source, dietary vitamin D is also important. Vitamin D3 is most often derived from animal products, though vegan D3 supplements made from lichen are available. Many fortified foods also contain vitamin D.
Zinc: Phytates in whole grains and legumes can inhibit zinc absorption. Vegetarians should ensure a consistent intake from sources like nuts, seeds, and beans.

A Comparison of Vitamin B12 Sources for Vegetarians


Source	Availability in Diet	Reliability for B12	Who Needs to Pay Attention?
Eggs and Dairy	Only for lacto-ovo and lacto-vegetarians	Variable; may not provide enough B12 for all individuals, especially over time.	Those with low consumption, and all lacto-ovo and lacto-vegetarians over 50 years of age.
Fortified Foods	Available for all vegetarians and vegans (check labels)	Highly reliable if consumed regularly and consistently.	All vegans and many vegetarians, especially those who avoid or limit dairy and eggs.
Supplements	Available for all dietary patterns	Most reliable and easily controllable source.	All vegans and those who struggle to meet requirements from fortified foods or diet alone.
Fermented Foods (e.g., tempeh, miso)	Present in many vegetarian and vegan diets	Unreliable; often contains inactive B12 analogues that interfere with absorption.	All individuals; should not be relied upon as a primary B12 source.

Symptoms and Proactive Monitoring

Early signs of B12 deficiency can be subtle, but if they persist, they should prompt a visit to a healthcare provider.

Common Symptoms of B12 Deficiency

Persistent fatigue and weakness
Tingling or numbness in hands and feet
Anemia, which can cause pale skin and shortness of breath
A painful, smooth, or swollen tongue
Changes in mood, memory, or cognitive function

Proactive monitoring is crucial, especially for long-term vegetarians and vegans. A doctor can test B12 levels via a blood test. More advanced testing, such as measuring homocysteine or methylmalonic acid (MMA), may be recommended for a more accurate assessment of cellular B12 status.

Conclusion: A Well-Planned Diet is Key

A vegetarian diet can be healthful and nutritionally adequate for all life stages, but it requires mindful planning to address specific nutrient gaps. Of all the potential deficiencies, vitamin B12 is the most critical for vegetarians and vegans to monitor. Relying on a combination of fortified foods and targeted supplementation is the most effective and reliable strategy to ensure sufficient B12 intake and prevent long-term health complications. Regularly consulting a healthcare professional or registered dietitian for advice and monitoring can provide extra assurance that your plant-based diet supports your best health.

For more information on the nutrient needs for a vegetarian lifestyle, consult reliable resources such as the Academy of Nutrition and Dietetics at eatright.org.

Frequently Asked Questions

Vegans, who consume no animal products, are at the highest risk for B12 deficiency. Lacto-ovo-vegetarians who consume eggs and dairy have a lower risk, but many may still need fortified foods or supplements to meet their needs, especially with age.

There are very few reliable, natural plant-based sources of active B12. Fortified foods like cereals, plant-based milks, and nutritional yeast are the most dependable vegan options, as the B12 is added intentionally.

Symptoms can include fatigue, weakness, pale skin, shortness of breath, a sore tongue, and neurological issues like tingling or numbness in the hands and feet. In severe cases, it can cause memory loss and confusion.

The human body can store B12 for several years, so deficiency symptoms can take a long time to appear. It could be anywhere from 2 to 10 years, depending on the individual's stored reserves and intake.

While consuming dairy and eggs reduces the risk, it does not eliminate it. Many factors affect absorption, and intake can vary. For this reason, many dietitians recommend supplements, particularly for those over 50 or those with limited intake.

A deficiency is typically diagnosed through a blood test that measures your serum B12 levels. To get a more accurate picture of your cellular B12 status, doctors may also test for elevated levels of homocysteine or methylmalonic acid (MMA).

No, you should not rely on these. The B12 found in some fermented foods and seaweeds is often an inactive form that the body cannot use effectively. These products are not considered reliable sources for meeting B12 needs.