What Does B12 Deplete? Understanding the Causes of Deficiency

October 20, 2025 •

3 min read

According to the National Institutes of Health, up to 20% of adults aged 60 and over may have a vitamin B12 deficiency. This shortfall can arise from various factors that interfere with the body's ability to absorb or retain this essential nutrient, leading many to ask: what does B12 deplete?

Quick Summary

Several factors can cause vitamin B12 levels to drop, including dietary inadequacies, malabsorption issues from digestive conditions or surgeries, and the long-term use of certain medications. Lifestyle habits like excessive alcohol use and specific medical conditions like pernicious anemia are also major contributors to a B12 deficit.

Key Points

Dietary Restrictions: Vegan and vegetarian diets require supplementation or fortified foods to prevent B12 deficiency, as the vitamin is primarily found in animal products.
Medication Interference: Long-term use of certain drugs, including metformin for diabetes and acid-reducing medications like PPIs, can impair B12 absorption.
Autoimmune Conditions: Pernicious anemia is a common autoimmune disorder that prevents the body from producing intrinsic factor, a protein necessary for B12 absorption.
Digestive Health Issues: Inflammatory bowel diseases, bacterial overgrowth, and gastric surgeries can all damage the gut's ability to absorb B12 effectively.
Lifestyle Habits: Excessive alcohol consumption and the use of nitrous oxide can deplete B12 levels and lead to deficiency.
Early Diagnosis is Crucial: Because neurological damage from B12 deficiency can be irreversible, early screening and diagnosis are vital for high-risk individuals.

Vitamin B12, or cobalamin, is a water-soluble vitamin vital for nerve function, red blood cell formation, and DNA synthesis. While the body can store B12 for several years, its levels can be depleted by a range of issues, from dietary restrictions to underlying health conditions and medication side effects. Understanding these causes is the first step toward prevention and treatment.

Dietary and Lifestyle Factors that Deplete B12

Vegan and Vegetarian Diets

Vitamin B12 is almost exclusively found in animal products, including meat, fish, poultry, eggs, and dairy. Consequently, individuals following a strict vegan or vegetarian diet are at a high risk for B12 deficiency if they do not supplement or consume fortified foods. The body's large stores can mask a deficiency for years, but symptoms can emerge over time.

Excessive Alcohol Consumption

Chronic and excessive alcohol use can severely damage the digestive tract, impairing the body's ability to absorb nutrients, including vitamin B12. Alcohol can also lead to liver damage, which is where the body stores the majority of its B12.

Recreational Drug Use

Repeated exposure to nitrous oxide, commonly known as laughing gas, can inactivate vitamin B12 in the body. This can lead to a functional B12 deficiency, with potentially severe neurological side effects.

Medical Conditions Affecting B12 Absorption

Pernicious Anemia

This is a leading cause of B12 deficiency, especially in older adults and people of Northern European descent. Pernicious anemia is an autoimmune disease where the body's immune system attacks the stomach cells that produce intrinsic factor. Intrinsic factor is a protein essential for the absorption of B12 in the small intestine. Without intrinsic factor, dietary B12 cannot be absorbed, regardless of how much is consumed.

Gastrointestinal Disorders and Surgery

Several conditions can prevent the proper absorption of vitamin B12 in the digestive system. These include:

Crohn's Disease and Celiac Disease: These inflammatory bowel conditions can damage the lining of the small intestine, specifically the ileum, where B12 is absorbed.
Atrophic Gastritis: This condition, often seen in older adults, involves the thinning of the stomach lining. It results in decreased production of hydrochloric acid, which is needed to separate B12 from food proteins for absorption.
Gastric Surgery: Procedures like gastric bypass surgery for weight loss or the surgical removal of parts of the stomach or small intestine can dramatically reduce the body's capacity to absorb B12.
Small Intestinal Bacterial Overgrowth (SIBO): An overgrowth of bacteria in the small intestine can lead to the bacteria consuming B12 before the body has a chance to absorb it.

Parasitic Infection

Infection with the fish tapeworm (Diphyllobothrium latum) can cause B12 deficiency, as the parasite competes with the human host for the vitamin.

Medications Known to Deplete B12

Long-term use of certain medications can interfere with B12 absorption. A consultation with a healthcare provider is important for managing B12 levels when on these drugs.


Medication Category	Examples	Mechanism of B12 Depletion
Proton Pump Inhibitors (PPIs)	Omeprazole, Lansoprazole	Reduce stomach acid, which is needed to release B12 from food proteins.
H2 Blockers	Famotidine	Reduce stomach acid, impairing B12 release from food.
Metformin	Glucophage	Reduces B12 absorption in the small intestine, particularly with higher doses and prolonged use.
Antibiotics	Various	Long-term use can disrupt intestinal flora, impacting absorption.
Colchicine	Used for gout	Can interfere with B12 absorption.

How to Manage Potential B12 Depletion

If you have risk factors for B12 deficiency, such as following a vegan diet or taking specific medications long-term, it's crucial to discuss your concerns with a doctor. They may recommend regular blood tests to check your B12 levels, along with other markers like methylmalonic acid (MMA) and homocysteine, which can provide more sensitive indicators of a functional deficiency. For those with dietary limitations or malabsorption issues, supplementation through oral pills or injections may be necessary. Early diagnosis and treatment are key to preventing the potentially irreversible neurological damage associated with a severe B12 deficiency. The National Institutes of Health provides excellent information on the topic at ods.od.nih.gov/factsheets/VitaminB12-Consumer/.

Conclusion

Numerous factors can cause a B12 deficiency, extending beyond a simple lack of dietary intake. From autoimmune conditions like pernicious anemia to common medications for acid reflux and diabetes, and even lifestyle choices, the reasons for depletion are diverse. By understanding what can interfere with B12, individuals can be proactive about their health. Regular medical consultation, monitoring through appropriate blood tests, and targeted supplementation can effectively manage and prevent the health complications associated with low vitamin B12 levels.

Frequently Asked Questions

Common medications that can cause low B12 levels include proton pump inhibitors (PPIs), H2 blockers for acid reflux, metformin for diabetes, and some antibiotics used long-term.

Since B12 is found almost exclusively in animal products, vegan and vegetarian diets can lead to a deficiency. Individuals on these diets must consume B12-fortified foods or take supplements to maintain adequate levels.

Pernicious anemia is an autoimmune condition where the body attacks the stomach cells that produce intrinsic factor. Without this protein, the body cannot absorb dietary B12, leading to a deficiency.

Yes, chronic and excessive alcohol use can damage the digestive system and liver, impairing the body's ability to absorb and store vitamin B12.

Conditions such as Crohn's disease, celiac disease, atrophic gastritis, and small intestinal bacterial overgrowth (SIBO) can interfere with the proper absorption of B12.

Doctors can test for a B12 deficiency using a blood test to check serum B12 levels. In some cases, additional tests for methylmalonic acid (MMA) and homocysteine may be performed for a more sensitive diagnosis.

Early treatment with B12 supplementation can reverse many neurological symptoms. However, if a deficiency is left untreated for too long, some nerve damage may become permanent.