What Can Interfere with Vitamin B Absorption?

October 29, 2025 •

4 min read

According to the National Institutes of Health, many older adults struggle to absorb vitamin B12 from food due to reduced stomach acid. This highlights that a seemingly healthy diet is not always enough, and many factors can interfere with vitamin B absorption, leading to potential deficiencies and health complications.

Quick Summary

Several factors can inhibit the body's ability to absorb B vitamins effectively. These include medical conditions like autoimmune gastritis, certain medications, gastrointestinal surgeries, and a diet lacking in B12 sources. Addressing these underlying issues is crucial for maintaining proper B vitamin levels and preventing deficiency symptoms.

Key Points

Autoimmune Conditions: Diseases like pernicious anemia prevent the production of intrinsic factor, a protein vital for absorbing vitamin B12.
Gastrointestinal Surgery: Procedures such as gastric bypass can reduce stomach acid and bypass the part of the intestine where B12 is absorbed.
Medication Side Effects: Long-term use of certain drugs, including proton pump inhibitors (PPIs) and metformin, can significantly decrease B vitamin absorption.
Vegan Diets: Since vitamin B12 is primarily found in animal products, those on strict vegan diets require supplements or fortified foods to prevent deficiency.
Chronic Alcoholism: Excessive alcohol intake damages the stomach and liver, leading to inflammation and impaired absorption and storage of B vitamins.
Age-Related Issues: As people age, reduced stomach acid production can hinder the release of B12 from food, making absorption more difficult.
Malabsorption Disorders: Conditions like Crohn's and celiac disease cause inflammation and damage to the digestive tract, impairing overall nutrient uptake.

Understanding the Complexities of B Vitamin Absorption

Vitamin B is not a single entity but a complex of eight water-soluble vitamins, including B1 (thiamin), B2 (riboflavin), B3 (niacin), B5 (pantothenic acid), B6 (pyridoxine), B7 (biotin), B9 (folate), and B12 (cobalamin). Each plays a unique and essential role in the body's metabolic processes. Unlike fat-soluble vitamins, most B vitamins are not stored in the body in large amounts (with the exception of B12 and folate, which are stored in the liver), meaning a consistent dietary intake is necessary. The intricate absorption process involves several steps, particularly for vitamin B12, starting with the release from food by stomach acid and its subsequent binding to a protein called intrinsic factor. Interference at any stage of this process can significantly impede absorption.

Medical Conditions That Impair Absorption

Numerous health conditions can prevent the body from properly absorbing B vitamins from food, with vitamin B12 malabsorption being particularly common.

Digestive and Autoimmune Disorders

Atrophic Gastritis: A chronic inflammatory condition of the stomach common in older adults, it reduces the production of hydrochloric acid and intrinsic factor, both essential for B12 absorption.
Pernicious Anemia: An autoimmune condition where the body's immune system attacks and destroys the stomach cells responsible for producing intrinsic factor. Without intrinsic factor, vitamin B12 cannot be absorbed, leading to a severe deficiency.
Inflammatory Bowel Diseases (IBD): Conditions like Crohn's disease and celiac disease cause inflammation in the digestive tract, which can damage the lining and interfere with nutrient absorption, including B vitamins. Celiac disease, for example, damages the small intestine where absorption occurs.
Chronic Pancreatitis: The pancreas produces enzymes necessary for digestion. Chronic pancreatic disease can lead to a deficiency of these enzymes, impairing the release and binding of vitamins like B12.

Gastrointestinal Surgery

Major surgeries involving the digestive system can profoundly impact vitamin absorption.

Bariatric Surgery: Procedures such as gastric bypass or sleeve gastrectomy alter the structure of the stomach and small intestine. This can lead to a loss of the cells that produce intrinsic factor or bypass the section of the small intestine (terminal ileum) where the B12-intrinsic factor complex is absorbed, leading to malabsorption.
Gastrectomy or Ileal Resection: The surgical removal of part or all of the stomach (gastrectomy) or the terminal ileum can severely compromise the body's ability to absorb B12.

Medications That Can Interfere

Several common medications can disrupt the body's ability to absorb B vitamins. It is important to discuss any long-term medication use with a healthcare provider to monitor for potential deficiencies.

Comparison Table of Medications Interfering with B Vitamin Absorption


Medication Class	Example Medications	Mechanism of Action	Affected B Vitamins
Gastric Acid Inhibitors	Omeprazole (Prilosec), Lansoprazole (Prevacid)	Reduce stomach acid, which is needed to release B12 from food protein.	Primarily B12
Diabetes Medication	Metformin	Decreases B12 absorption in the intestines.	Primarily B12
H2-Receptor Antagonists	Cimetidine (Tagamet), Ranitidine (Zantac)	Also reduce stomach acid, interfering with B12 release from food.	B12
Antiseizure Drugs	Phenytoin (Dilantin), Carbamazepine (Tegretol)	Can lower levels of both vitamin B12 and folate.	B12, Folate
Certain Antibiotics	Chloramphenicol	Can interfere with the proper utilization of B vitamins.	B12
Anti-inflammatory Drugs	Colchicine	May interfere with B12 absorption.	B12

Dietary and Lifestyle Factors

Beyond medical conditions and medication, daily habits and dietary choices also play a critical role in B vitamin absorption.

Dietary Choices

Vegan or Vegetarian Diets: Vitamin B12 is found naturally only in animal products like meat, eggs, and dairy. Vegans and strict vegetarians must rely on fortified foods or supplements to meet their B12 requirements, as dietary intake alone is insufficient.
Excessive Folic Acid: While folate (B9) is crucial, very high supplemental doses can potentially mask a vitamin B12 deficiency, delaying diagnosis and treatment. It is recommended to take balanced B-complex supplements rather than high doses of a single B vitamin.
Food Processing and Cooking: B vitamins are water-soluble and can be destroyed by heat and excessive cooking. Food processing, such as turning whole grains into white flour, also removes these vitamins.

Alcohol Consumption

Chronic and heavy alcohol use is a major inhibitor of B vitamin absorption.

Damages Digestive System: Alcohol irritates the stomach and intestinal lining, causing inflammation (gastritis), which reduces the absorption of nutrients.
Impairs Storage: Vitamin B12 is primarily stored in the liver. Excessive alcohol consumption can damage the liver, impairing its ability to store and utilize vitamin B12 effectively.
Increases Excretion: Alcohol can also lead to increased urinary excretion of certain B vitamins, further depleting body stores.

Conclusion: Navigating Absorption Challenges

Poor absorption of B vitamins is a common issue with a wide range of causes, from underlying medical conditions and essential medications to everyday dietary choices and lifestyle habits. Factors such as aging, autoimmune diseases like pernicious anemia, and gastrointestinal surgeries can disrupt the complex process required for absorption. Furthermore, long-term use of certain medications, such as acid inhibitors and metformin, can interfere with vitamin B12 uptake. For those following vegan or vegetarian diets, intentional supplementation is key, while chronic alcohol use can damage the digestive tract and deplete body stores of B vitamins. Recognizing these potential issues and working with a healthcare provider is essential for addressing malabsorption, ensuring adequate nutrient levels, and preventing serious long-term health consequences. Taking action to manage underlying conditions and dietary risks can help maintain optimal vitamin B status.

Frequently Asked Questions

Vitamin B12 (cobalamin) is particularly susceptible to absorption issues because its complex process depends on adequate stomach acid and a protein called intrinsic factor. Conditions affecting the stomach and small intestine most often interfere with B12 absorption.

For some causes of malabsorption, such as low stomach acid in older adults, B-complex supplements can be effective because they contain B12 in a free, more easily absorbed form. However, severe issues like pernicious anemia or post-bariatric surgery malabsorption often require injections.

Metformin, a common diabetes medication, can lower vitamin B12 levels by interfering with its absorption in the intestines. Doctors often monitor B12 levels in long-term metformin users and may recommend supplementation.

For B12 found in food, hydrochloric acid in the stomach is required to release the vitamin from the protein it's bound to. Without sufficient stomach acid, this release doesn't happen efficiently, preventing the next steps of the absorption process.

No. While they are all water-soluble, their absorption mechanisms differ. Vitamin B12's pathway involving intrinsic factor is unique, while other B vitamins like riboflavin and niacin are absorbed through passive transport or different carrier systems.

Yes, inflammation in the digestive system, caused by conditions such as Crohn's disease, celiac disease, or gastritis, can damage the lining of the stomach and intestines. This damage impairs the body's ability to properly absorb nutrients, including B vitamins.

Symptoms of B vitamin deficiency can be varied and may include fatigue, tingling in the hands and feet, weakness, pale skin, or nerve damage. A diagnosis should be confirmed with blood tests ordered by a healthcare provider.