Understanding Why You Might Be Asking, 'What can cause depletion of B12?'

October 16, 2025 •

3 min read

While the body stores several years' worth of vitamin B12, approximately 10–30% of adults over 65 may experience malabsorption, making them susceptible to depletion. Understanding what can cause depletion of B12 is critical for recognizing risk factors and maintaining optimal health.

Quick Summary

Several factors, from insufficient dietary intake to medical conditions and medications, can lead to vitamin B12 depletion. Poor absorption is the most common cause, especially in older adults and those with gastrointestinal disorders.

Key Points

Dietary Intake: Strict vegans and vegetarians are at high risk of B12 depletion due to the absence of animal products, the primary natural source of the vitamin.
Pernicious Anemia: This autoimmune condition, preventing intrinsic factor production, is a common cause of B12 deficiency.
Malabsorption: Digestive disorders and surgeries like Crohn's, celiac disease, and bariatric surgery can impair B12 absorption.
Medication Side Effects: Drugs like metformin and acid reducers (PPIs) can decrease B12 levels.
Aging and Alcohol Use: Reduced stomach acid in older adults and alcohol abuse can hinder B12 absorption.
Underlying Health Conditions: Chronic illnesses, including advanced HIV and autoimmune disorders like Sjögren's syndrome, increase the risk.

The Importance of Vitamin B12

Vitamin B12, or cobalamin, is a vital water-soluble nutrient essential for red blood cell production, DNA synthesis, and maintaining a healthy nervous system. A deficiency can manifest as fatigue, weakness, or neurological problems. Although the body stores a significant amount of B12, these reserves can be exhausted if the underlying cause of depletion isn't addressed.

Dietary Insufficiency: Where is the B12?

B12 is primarily found in animal-based foods. Therefore, dietary choices significantly impact B12 levels.

Vegan and Strict Vegetarian Diets: Individuals avoiding animal products are at high risk of depletion and need B12 from fortified foods or supplements. Symptoms may not appear for years as the body uses its stores.
Infants of Vegan Mothers: Breastfed infants of B12-deficient vegan mothers are vulnerable to severe deficiency, impacting development and neurology.
General Poor Intake: While uncommon in those who eat animal products, a consistently poor diet can also lead to B12 depletion over time.

Fortified cereals, plant-based milks, nutritional yeast, and oral supplements are crucial B12 sources for individuals with restrictive diets.

Malabsorption: The Body's Biggest Hurdle

Inadequate absorption is a more frequent cause of B12 deficiency than low dietary intake. Absorption relies on stomach acid and intrinsic factor, a protein.

The Intrinsic Factor Connection

Pernicious Anemia: This autoimmune condition causes the body to attack stomach cells that produce intrinsic factor, preventing B12 absorption in the small intestine.
Atrophic Gastritis: Inflammation and thinning of the stomach lining, often due to autoimmune issues or H. pylori, reduce stomach acid and intrinsic factor needed for B12 release from food. This is common in older adults.

Digestive System Disorders and Surgery

Conditions and surgeries affecting the digestive tract can hinder B12 absorption. This includes conditions like Crohn's disease and celiac disease, as well as procedures like bariatric surgery.

Medication Interactions and Lifestyle Factors

Certain medications and lifestyle choices can contribute to B12 depletion. These include gastric acid inhibitors, metformin, and excessive alcohol consumption. Age can also be a factor, as reduced stomach acid is common in older adults.

Comparing Causes of B12 Depletion


Feature	Dietary Insufficiency	Malabsorption (e.g., Pernicious Anemia)
Cause	Lack of B12-rich foods (primarily animal products) in the diet.	Impaired digestive function preventing B12 absorption.
At-Risk Groups	Vegans, strict vegetarians, infants of vegan mothers.	Older adults, individuals with autoimmune diseases or gastrointestinal disorders.
Absorption	Can be effectively treated with oral supplements.	Oral supplements may be ineffective; often requires injections.
Onset	Can be slow, with body stores lasting several years.	Can be slow but may present with more severe symptoms.

Conclusion

Identifying what can cause depletion of B12 is crucial for treatment and prevention. Causes range from dietary deficiencies to complex medical issues. Malabsorption is a significant factor, particularly in older adults. Individuals with risk factors or symptoms should consult a healthcare provider for diagnosis and treatment. Addressing the root cause is vital for restoring B12 and maintaining health.

For more detailed information on vitamin B12, visit the {Link: NIH Office of Dietary Supplements website https://ods.od.nih.gov/factsheets/VitaminB12-Consumer/}.

Frequently Asked Questions

Yes, a vegan diet can cause vitamin B12 deficiency because B12 is found naturally only in animal products. Vegans must consume fortified foods or take supplements to meet their needs.

Pernicious anemia is an autoimmune disease where the body cannot produce intrinsic factor, a protein needed to absorb B12 from the stomach. This is a major cause of B12 deficiency.

As people get older, the production of stomach acid often decreases. Since stomach acid is necessary to release vitamin B12 from food, this can lead to poor absorption of the nutrient over time.

Yes, several medications can interfere with B12 absorption. Examples include metformin for diabetes and gastric acid inhibitors like proton pump inhibitors (PPIs) and H2 blockers.

Digestive diseases such as Crohn's and celiac disease can cause inflammation or damage to the small intestine, particularly the ileum, where B12 is absorbed. This impairs the body's ability to take in the vitamin.

Early signs often include fatigue, weakness, lack of energy, and a sore or red tongue. Neurological symptoms like tingling in the hands and feet can also develop.

Treatment varies depending on the cause. It can range from oral supplements for dietary deficiencies to injections for malabsorption issues like pernicious anemia. A healthcare provider will determine the best course of action.