Can You Get a B12 Deficiency from Not Eating?

December 17, 2025 •

3 min read

According to the National Institutes of Health, people who do not consume enough vitamin B12 through fortified foods or animal products can develop a deficiency. While the body can store B12 for several years, a prolonged lack of dietary intake will eventually deplete these reserves and cause problems.

Quick Summary

A vitamin B12 deficiency is possible from inadequate dietary intake, especially for vegans and vegetarians, or due to malabsorption issues. It is crucial to identify the root cause for effective treatment and management.

Key Points

Diet is a Primary Factor: B12 is naturally found in animal products, so a diet lacking these foods (like a vegan diet) is a direct risk factor for deficiency.
Malabsorption is Also Common: Beyond diet, many conditions like pernicious anemia, gastritis, Crohn's disease, and gastric surgery can prevent the body from absorbing B12.
Deficiency Can Take Years to Appear: The body stores a large amount of B12, so symptoms from dietary changes may not show up for years, making regular monitoring crucial.
Symptoms are Varied and Serious: Signs include fatigue, neurological issues like tingling and numbness, psychological changes, and in severe cases, irreversible nerve damage.
Treatment Depends on the Cause: Oral supplements are effective for dietary deficiencies, while injections are often necessary for malabsorption problems to bypass the gut.
Fortified Foods and Supplements are Key: At-risk individuals, including vegans and older adults, can prevent deficiency by consistently consuming fortified foods and/or supplements.

Understanding the Role of Vitamin B12

Vitamin B12, or cobalamin, is an essential water-soluble vitamin crucial for brain function, the nervous system, red blood cell formation, and DNA synthesis. The body stores significant amounts, primarily in the liver, for several years. This means deficiencies due to dietary changes, like going vegan, might take time to appear. However, by the time symptoms manifest, reserves are likely low. A major cause of vitamin B12 deficiency is insufficient dietary intake, as it's primarily found in animal products.

The Direct Link: Diet and B12 Deficiency

Not eating enough B12-rich foods can indeed lead to a deficiency. Strict vegans, who avoid all animal products, are particularly vulnerable. Vegetarians consuming eggs and dairy may get some B12, but intake can still be insufficient. To address dietary deficiency, incorporate reliable B12 sources:

Fortified Plant Milks: Soy, almond, and oat milks often contain added B12.
Nutritional Yeast: Fortified nutritional yeast is a good vegan source.
Fortified Breakfast Cereals: Many cereals are fortified; check labels.
Supplements: Regular B12 supplements are often recommended for vegans.

Beyond Diet: Malabsorption Issues

Even with sufficient dietary intake, B12 deficiency can occur if the body cannot absorb it properly. Malabsorption can stem from issues with the digestive system. Non-dietary causes include:

Pernicious Anemia: An autoimmune condition where the body attacks stomach cells producing intrinsic factor, essential for B12 absorption.
Chronic Gastritis: Inflammation of the stomach lining can reduce acid needed to free B12 from food.
Gastrointestinal Surgery: Procedures like gastric bypass can impair absorption.
Digestive Diseases: Conditions like Crohn's and celiac disease can damage the B12 absorbing parts of the intestine.
Medications: Certain drugs, including long-term PPIs and metformin, can lower B12 levels.

Symptoms and Complications of Deficiency

B12 deficiency symptoms often develop slowly and affect physical and neurological health. Signs can include:

Fatigue and Weakness: A common physical symptom.
Neurological Issues: Tingling or numbness in extremities (peripheral neuropathy) is a classic sign.
Psychological Changes: Irritability, depression, confusion, memory loss, and in severe cases, paranoia.
Megaloblastic Anemia: Production of abnormally large red blood cells, causing paleness, dizziness, and rapid heart rate.
Sore or Red Tongue: Known as glossitis, often with mouth ulcers.
Mobility Issues: Problems with balance and coordination in advanced cases.

Comparing Dietary vs. Malabsorption B12 Deficiency

Identifying the cause – dietary lack or malabsorption – is vital for treatment. The table below highlights key differences:


Feature	Dietary Deficiency	Malabsorption (e.g., Pernicious Anemia)
Underlying Cause	Insufficient intake of B12 foods.	Inability to absorb B12 due to digestive issues.
Absorption Mechanism	Normal digestion, but lack of dietary B12.	Impaired absorption in small intestine.
Treatment Method	High-dose oral supplements or fortified foods.	Initial injections often needed, followed by ongoing injections or high-dose oral therapy.
Preventive Strategy	Consistent supplements or fortified foods.	Regular medical monitoring and prescribed treatment.

Diagnosis, Treatment, and Prevention

Diagnosis

Diagnosis involves blood tests. A full blood count (CBC) may show large red blood cells. A vitamin B12 test measures blood levels. A methylmalonic acid (MMA) test can further confirm deficiency.

Treatment

Treatment depends on the cause. For dietary deficiencies, high-dose oral supplements are usually effective. Malabsorption often requires hydroxocobalamin injections to bypass the digestive system. A lifelong treatment plan, either with injections or high-dose oral supplements, is often necessary for malabsorption.

Prevention

Prevention is crucial for those at risk. Vegans and vegetarians should include fortified foods and/or supplements. Older adults, prone to reduced stomach acid, may also benefit from supplements. Individuals with chronic digestive conditions or on relevant medications require regular medical monitoring. Consult a doctor or dietitian for personalized prevention advice.

Conclusion

Yes, you can develop a B12 deficiency from not eating enough B12-rich foods, primarily because it's naturally found in animal products. However, medical conditions affecting absorption can also cause deficiency, regardless of diet. Given the risk of serious and irreversible neurological damage, individuals with risk factors should ensure adequate B12 intake through monitoring and supplementation.

For more detailed information on vitamin B12 and its health effects, see the NIH Office of Dietary Supplements Fact Sheet.

Frequently Asked Questions

Because the body stores large reserves of B12, it can take anywhere from three to five years after removing animal products from the diet for a deficiency to develop. This is why consistent supplementation is essential for vegans, even early on.

While vegetarian diets, which include eggs and dairy, contain some B12, intake may still be inadequate for some individuals. It is important to monitor B12 levels and consider fortified foods or supplements to ensure you meet daily requirements.

The initial symptoms often include fatigue, weakness, a sore or red tongue, and mild neurological issues such as tingling or numbness in the hands and feet.

Diagnosis is typically made through blood tests, including a complete blood count (CBC) to check for large red blood cells, and a serum vitamin B12 level test. Further tests, like a methylmalonic acid (MMA) test, may be used for confirmation.

Yes. Malabsorption conditions, such as pernicious anemia, chronic gastritis, or intestinal surgery, can prevent your body from absorbing B12 properly, regardless of your dietary intake.

For dietary-related deficiencies, high-dose oral B12 supplements are generally very effective. However, for malabsorption issues, injections may be required.

Conditions such as pernicious anemia, Crohn's disease, celiac disease, gastritis, and surgical removal of parts of the stomach or small intestine can all lead to B12 malabsorption.