Is it possible to have no B12?

October 9, 2025 •

3 min read

According to the National Institutes of Health, vitamin B12 deficiency can take years to develop because the body stores substantial amounts of it in the liver. The idea of having absolutely no B12 is highly improbable for most people, but severe deficiency can occur due to long-term poor intake or medical conditions that prevent absorption.

Quick Summary

The human body stores vitamin B12, making a complete absence unlikely, yet severe deficiencies can develop due to dietary restrictions, particularly veganism, or impaired absorption from conditions like pernicious anemia. Untreated deficiency can lead to serious and irreversible neurological problems, as well as megaloblastic anemia. Treatment involves addressing the underlying cause and supplementing with B12 via appropriate methods.

Key Points

Absolute Zero is Improbable: While you won't have 'zero' B12, severe deficiency is possible once the liver's multi-year stores are depleted.
Veganism and B12: A strict vegan diet without reliable sources like fortified foods or supplements is a major risk factor for deficiency.
Pernicious Anemia Causes Malabsorption: This autoimmune disease prevents the absorption of B12, requiring lifelong administration methods.
Neurological Damage is a Risk: Untreated severe deficiency can lead to permanent nerve damage, balance issues, and cognitive decline.
Symptoms are Gradual: The slow onset of B12 deficiency symptoms, such as fatigue and tingling, can make it difficult to diagnose early.
Absorption Issues from Medication: Some common medications, including those for diabetes and heartburn, can interfere with B12 absorption.
Proper Treatment is Essential: Depending on the cause, B12 deficiency is treated with appropriate methods, such as oral supplements or injections, to replenish levels.
Early Diagnosis Prevents Permanent Damage: Promptly seeking medical advice and treatment upon suspecting a deficiency is crucial to prevent irreversible complications.

Understanding the role of Vitamin B12

Vitamin B12, also known as cobalamin, is a crucial nutrient for several fundamental bodily functions. It plays a vital role in maintaining the health of your nerve cells and red blood cells, and it is essential for the formation of DNA, the genetic material in all your cells. The human body does not produce its own vitamin B12; therefore, it must be obtained from external sources, primarily animal products and fortified foods. A long-term lack of this essential vitamin can lead to a condition known as vitamin B12 deficiency, which, if left untreated, can result in serious and potentially irreversible neurological and hematological issues.

The improbability of zero B12

While having 'zero' B12 is unlikely, a state of near-total depletion is a serious medical issue. The body stores significant B12 reserves in the liver, lasting two to five years. However, once depleted, severe deficiency can occur, with symptoms developing slowly.

Key causes of severe B12 deficiency

Severe B12 deficiency can result from dietary issues or malabsorption problems.

Dietary causes

A balanced diet with animal products typically provides sufficient B12.

Vegan Diet: Strict vegans are at high risk and require fortified foods or supplements as B12 is primarily in animal products.
Poor Diet: Long-term restricted diets, common in older adults or those with alcohol use disorder, can lead to deficiency.

Malabsorption issues

These conditions hinder B12 absorption. Intrinsic factor, produced in the stomach, is vital for B12 absorption. Pernicious anemia attacks intrinsic factor-producing cells, preventing B12 absorption. Stomach and intestinal surgery can impair intrinsic factor production or the absorption site. Chronic digestive disorders and certain medications can also interfere with B12 absorption.

The consequences of severe B12 depletion

Severe B12 depletion can cause neurological symptoms like tingling, numbness, balance problems, cognitive decline, and psychological issues. It can also lead to megaloblastic anemia and general anemia symptoms like fatigue and weakness.

A comparison of B12 deficiency and pernicious anemia


Feature	Vitamin B12 Deficiency (General)	Pernicious Anemia
Cause	Can be dietary (e.g., veganism), age-related, drug-induced, or due to malabsorption.	An autoimmune condition causing the body to attack cells producing intrinsic factor.
Mechanism	Inadequate intake, poor release from food proteins (low stomach acid), or intestinal damage.	Inability to absorb B12 due to a lack of intrinsic factor.
Onset	Can develop gradually over several years as the body's stores are depleted.	Typically insidious; symptoms often appear after age 50.
Treatment	May involve appropriate supplementation methods or fortified foods, potentially combined with managing the underlying cause.	Lifelong treatment with appropriate B12 administration is often required, as oral supplements are not effectively absorbed in many cases.

Conclusion: Preventing and managing B12 deficiency

While having no B12 is unlikely, severe deficiency poses real risks of permanent damage. Since the body can't produce this vitamin and stores deplete, proactive management is vital for at-risk groups. Maintaining adequate B12 through diet, fortification, or supplements for vegans, and lifelong management for pernicious anemia, is crucial for health. Consult a healthcare provider for diagnosis and treatment if you suspect deficiency.

This article is for informational purposes only and is not a substitute for professional medical advice. Always consult with a qualified healthcare provider for any health concerns or before making changes to your diet or treatment plan.

The Vegan Society's Guidelines on B12 for Vegans

The Vegan Society recommends vegans ensure adequate B12 intake via fortified foods or supplements to meet their needs {Link: The Vegan Society website https://www.vegansociety.com/resources/nutrition-and-health/nutrients/vitamin-b12/what-every-vegan-should-know-about-vitamin-b12}.

For more information, visit the What Every Vegan Should Know About Vitamin B12 page on The Vegan Society website.

Frequently Asked Questions

No, having absolutely zero B12 is not sustainable for human life. The body stores significant amounts of B12 in the liver, which can sustain bodily functions for several years. However, a severe and prolonged deficiency, once these reserves are depleted, can lead to serious and irreversible damage to the nervous system and blood cells.

Since the body stores a large reserve of vitamin B12, it can take several years, often between three to five, for a deficiency to develop after dietary intake ceases or absorption problems begin. The symptoms also tend to appear gradually, making early detection difficult.

Pernicious anemia is an autoimmune condition and a common cause of B12 deficiency where the body's immune system attacks the stomach cells that produce intrinsic factor. Intrinsic factor is a protein essential for absorbing B12 from the digestive tract. This renders dietary B12 sources ineffective, requiring treatment with specific administration methods.

Early symptoms often include fatigue, weakness, and a lack of energy. As the deficiency progresses, more specific signs can appear, such as a sore or red tongue, pale skin, pins and needles (paraesthesia) in the hands and feet, and mood changes.

No, while dietary restrictions like veganism are a significant risk factor, malabsorption issues are a common cause of deficiency in the general population, especially among older adults. Conditions like pernicious anemia, Crohn's disease, and certain medications can also cause B12 deficiency regardless of diet.

Diagnosis is typically based on a combination of patient symptoms, a physical examination, and blood tests. A blood test measuring total serum B12 is standard, but in some cases, other markers like methylmalonic acid (MMA) or homocysteine may also be tested to confirm a functional deficiency.

Many symptoms, especially those related to anemia, can resolve with appropriate B12 treatment. However, if severe neurological damage has occurred, particularly in long-standing, untreated cases, some symptoms may become permanent.