What Keeps You From Absorbing B Vitamins?

December 9, 2025 •

3 min read

According to the National Institutes of Health, older adults with atrophic gastritis, a common cause of food-bound vitamin B12 malabsorption, represent a significant portion of those with B12 deficiency. Understanding the root cause is crucial for addressing poor absorption and maintaining optimal health.

Quick Summary

This article explores the common culprits behind poor B vitamin absorption, such as underlying medical conditions, certain medications, and lifestyle factors. We'll delve into the digestive process for B vitamins and provide guidance for optimizing your intake.

Key Points

Poor Absorption is Not Always About Diet: Even a nutritious diet can't prevent B vitamin deficiency if underlying medical conditions, medications, or genetic factors are interfering with absorption.
B12 Has a Unique Absorption Path: The process for absorbing vitamin B12 is complex, requiring both stomach acid and a protein called intrinsic factor, making it vulnerable to disruption.
Medications Can Cause Malabsorption: Common drugs for acid reflux and diabetes, like PPIs and metformin, can interfere with B12 absorption when taken long-term.
Lifestyle Habits Impact Absorption: Excessive alcohol use and adherence to a vegan diet are significant risk factors for B vitamin malabsorption and deficiency.
Gut Health Is Crucial: The balance of your gut microbiota is key, as an imbalance can lead to bacterial overgrowth that competes with your body for vital B vitamins.
Malabsorption Requires Professional Guidance: Diagnosing poor absorption requires clinical assessment and blood tests to determine the best course of treatment, which may include injections or high-dose supplements.

The Gut-Brain Axis: The Complex Journey of B Vitamins

B vitamins are essential water-soluble nutrients with vital roles in nearly every cell of the body. Their absorption is a complex process in the digestive system. While most B vitamins like B1, B2, and B6 are absorbed in the small intestine, B12 has a more involved route. B12 needs stomach acid to be released from food proteins and then must bind to intrinsic factor (produced in the stomach) before being absorbed in the ileum. Issues at any stage can impair absorption.

Gastrointestinal Disorders That Impair Absorption

Many digestive conditions can negatively impact B vitamin absorption:

Celiac Disease: Gluten damages the small intestine lining, hindering nutrient absorption, including B vitamins.
Inflammatory Bowel Diseases (Crohn's, Ulcerative Colitis): Inflammation and damage in the digestive tract, especially the ileum, can affect B12 absorption.
Atrophic Gastritis: Chronic stomach inflammation reduces stomach acid and intrinsic factor, both needed for B12 absorption.
Pernicious Anemia: An autoimmune form of atrophic gastritis where the body attacks intrinsic factor-producing cells, causing B12 malabsorption.
Small Intestinal Bacterial Overgrowth (SIBO): Excess bacteria in the small intestine can consume B vitamins, particularly B12.
Pancreatic Insufficiency: Impaired pancreatic enzyme production can affect the digestion of proteins needed to release B vitamins.

Medications That Block Absorption

Long-term use of certain medications can interfere with B vitamin absorption:

Metformin: This diabetes drug can reduce B12 absorption.
Acid Reducers (PPIs and H2 Blockers): Medications for acid reflux can lower stomach acid, which is needed to release B12 from food.
Antibiotics: Extended use may disrupt gut bacteria important for some B vitamin absorption.
Anticonvulsants: Some anti-seizure medications can interfere with B12 absorption.

Lifestyle and Surgical Factors Affecting Absorption

Lifestyle choices and certain surgeries can also play a role:

Excessive Alcohol: Chronic heavy drinking damages the digestive tract, impairs liver function, and reduces the absorption of several B vitamins.
Weight-Loss Surgery: Procedures like gastric bypass can reduce stomach size and affect the production of stomach acid and intrinsic factor, leading to B12 malabsorption.
Vegan/Vegetarian Diets: Since B12 is mainly found in animal products, plant-based diets require fortified foods or supplements to prevent deficiency.
Older Age: The natural aging process can reduce stomach acid and increase the risk of atrophic gastritis, affecting B12 absorption.

The Impact of Genetics and Microbiota

Genetics: Certain genetic factors, like the MTHFR gene mutation, can affect how the body metabolizes folate and B12. Rare conditions can also impair B12 transport.
Gut Microbiota: Gut bacteria contribute to B vitamin production but can also compete for them, especially in cases like SIBO. A healthy microbiome supports optimal vitamin absorption.

Comparison of Common B-Vitamin Absorption Issues


Factor	How It Affects B Vitamin Absorption	Primary B Vitamins Affected	Intervention/Management
Atrophic Gastritis	Decreases stomach acid and intrinsic factor production.	B12	Supplements (oral or injections), treating underlying cause.
Celiac Disease	Damages the small intestine lining, reducing absorptive surface.	All B vitamins, especially B12	Gluten-free diet.
Chronic Alcoholism	Damages stomach/intestinal lining; impairs liver's storage of B12.	B1, B6, B9, B12	Reduce/stop alcohol intake, supplementation.
Pernicious Anemia	Autoimmune attack on intrinsic factor-producing cells.	B12	B12 injections or high-dose oral supplements.
Metformin Use	Reduces B12 absorption in the intestine.	B12	Supplementation, regular monitoring.
Vegan/Vegetarian Diet	Lack of natural dietary sources.	B12	Fortified foods or supplementation.

Conclusion: Taking Control of Your B Vitamin Status

Recognizing factors that impede B vitamin absorption is key to preventing deficiency. Causes range from medical conditions and medications to lifestyle and genetics. Consulting a healthcare provider is essential, particularly for high-risk groups like older adults, vegans, or those on specific medications. Diagnosis, often through blood tests measuring homocysteine and methylmalonic acid (MMA), helps determine the best treatment plan, which may include diet changes, supplements, or injections. Proactive steps can ensure adequate intake of these vital nutrients for optimal health.

For more information on vitamin B12 deficiency, including symptoms, causes, and treatment options, visit the Cleveland Clinic at https://my.clevelandclinic.org/health/diseases/22831-vitamin-b12-deficiency.

Frequently Asked Questions

Symptoms can vary depending on the specific vitamin but often include fatigue, weakness, pale skin, shortness of breath, numbness or tingling in the hands and feet, confusion, and memory issues.

Yes, medications that reduce stomach acid, such as proton pump inhibitors (PPIs) and H2 blockers, can interfere with the body's ability to absorb vitamin B12 from food.

Chronic alcohol use can damage the stomach lining, impair the intestines' ability to absorb nutrients, and interfere with the liver's ability to store B12, leading to deficiencies.

Yes, because vitamin B12 is found almost exclusively in animal products, those on vegan or vegetarian diets are at higher risk of B12 deficiency without proper supplementation or consumption of fortified foods.

Pernicious anemia is an autoimmune condition where the body attacks the cells that produce intrinsic factor, a protein necessary for absorbing vitamin B12 in the small intestine. This results in severe B12 malabsorption.

Yes, procedures like gastric bypass can reduce stomach size and affect the parts of the digestive tract responsible for producing stomach acid and intrinsic factor, leading to vitamin B12 malabsorption.

Treatment depends on the cause but may involve injections of B12, high-dose oral supplements, or addressing the underlying medical condition, such as managing celiac or Crohn's disease.