Can B12 deficiency cause nausea? Uncovering the link to digestive issues

October 9, 2025 •

3 min read

According to Johns Hopkins Medicine, nausea is a possible symptom of vitamin B12 deficiency anemia. This can occur because a lack of this essential nutrient impacts red blood cell production, which is crucial for delivering oxygen to the digestive tract and other vital systems.

Quick Summary

Vitamin B12 deficiency is known to cause various gastrointestinal issues, including nausea, vomiting, and diarrhea. This connection is primarily due to the vitamin's role in healthy red blood cell production and proper oxygen supply to the gut, affecting digestive function.

Key Points

Nausea is a known symptom of B12 deficiency: It is listed alongside other digestive and systemic symptoms in medical literature.
Reduced oxygen supply to the gut can cause nausea: A lack of B12 impairs red blood cell production, decreasing oxygen to the digestive tract and causing distress.
B12 deficiency also affects nerve function: Nerve damage can disrupt normal digestive processes, contributing to feelings of nausea.
Other GI symptoms often accompany nausea: Diarrhea, constipation, bloating, and loss of appetite are common alongside B12-related nausea.
The deficiency is typically caused by malabsorption or diet: Common causes include pernicious anemia, stomach surgery, certain medications, and vegan or vegetarian diets.
Treatment involves supplements or injections: Depending on the cause and severity, a healthcare provider may recommend oral supplements or B12 injections to resolve the deficiency.

The Connection Between B12 Deficiency and Nausea

B12 deficiency can cause megaloblastic anemia, where the body produces large, ineffective red blood cells. These cells are less efficient at carrying oxygen, leading to reduced oxygen supply throughout the body, including the digestive tract. Insufficient oxygen in the gut can impair function and cause inflammation, resulting in symptoms like nausea and vomiting.

B12's Role in Nerve Health and Digestion

B12 is also critical for nerve health. Deficiency can cause nerve damage, which can disrupt the gut-brain axis and affect digestive processes, potentially contributing to nausea.

Other Gastrointestinal Symptoms Related to B12 Deficiency

Nausea may appear with other digestive symptoms of B12 deficiency, including:

Vomiting.
Diarrhea or constipation.
Loss of appetite and weight loss.
Bloating and gas.
A sore or red tongue (glossitis).

Common Causes of B12 Deficiency

The most common cause is poor absorption.

Dietary Factors

Vegans and vegetarians are at higher risk if they don't consume fortified foods or supplements, as B12 is mainly in animal products.

Malabsorption Issues

Several conditions and procedures hinder B12 absorption:

Pernicious anemia: An autoimmune condition affecting the absorption protein intrinsic factor.
Atrophic gastritis: Inflammation reducing stomach acid needed for B12 release.
Digestive diseases: Conditions like Crohn's and celiac disease can damage absorption sites in the intestine.
Stomach surgery: Procedures like gastric bypass can alter areas needed for absorption.

Medications

Some long-term medications, like PPIs and metformin, can interfere with B12 absorption.

Diagnosing and Treating B12 Deficiency

Consult a healthcare provider for persistent digestive issues and other symptoms like fatigue. Diagnosis involves blood tests. Treatment options include:

Supplements: Oral supplements for mild deficiencies or less severe malabsorption.
Injections: For severe deficiencies or pernicious anemia, bypassing the digestive system for direct absorption.
Dietary Adjustments: Increasing B12-rich foods or fortified products for those with dietary intake issues.

Comparison of B12-Related Nausea vs. Common Digestive Issues


Symptom	B12 Deficiency-Related Nausea	Common Digestive Issues (e.g., food poisoning, acid reflux)
Onset	Gradual and persistent, often accompanied by other non-GI symptoms like fatigue or pins and needles.	Sudden onset, often after consuming a specific food, or linked to specific dietary triggers.
Associated Symptoms	Fatigue, neurological symptoms (tingling, numbness), pale skin, glossitis, and irritability.	Usually localized to the GI tract, including stomach pain, bloating, or heartburn, without systemic symptoms.
Duration	Chronic and worsens over time if untreated, as the body's B12 stores are depleted.	Short-term, often resolving within a few hours to days, or episodic based on dietary triggers.
Underlying Cause	A systemic issue leading to poor red blood cell production and nerve function.	Infection, inflammation, dietary intolerance, or excess stomach acid.

What to Do If You Suspect a Deficiency

If you experience persistent nausea or other digestive issues alongside symptoms like fatigue or tingling, consult a healthcare professional for diagnosis and treatment. Early intervention is crucial to prevent long-term complications. You can read more about B12 deficiency anemia and related symptoms at Johns Hopkins Medicine.

Conclusion

Yes, B12 deficiency can cause nausea and other digestive problems. This is due to its role in red blood cell production and oxygen delivery to the gut. If you experience these issues, consult a doctor to check for a vitamin deficiency.

Frequently Asked Questions

A vitamin B12 deficiency can cause stomach issues because it leads to megaloblastic anemia, which impairs the delivery of oxygen to the digestive tract. The lack of oxygen and proper cell function in the gut can lead to inflammation and disrupt the digestive process, causing symptoms like nausea, vomiting, and diarrhea.

Nausea from a B12 deficiency often develops slowly and is accompanied by other symptoms like fatigue, tingling in the hands or feet, irritability, and pale skin. Nausea caused by other issues is often more acute or linked to a specific trigger. A blood test is the only way to confirm a B12 deficiency.

Yes, a vitamin B12 deficiency can cause both nausea and constipation. The disruption to the digestive system from poor oxygen supply can lead to a variety of irregular bowel movements.

The fastest way to treat a B12 deficiency and its symptoms, including nausea, is to address the underlying cause. In severe cases, a doctor may recommend B12 injections to quickly raise levels. For milder deficiencies or those with dietary issues, high-dose oral supplements may be effective.

Yes, once a B12 deficiency is diagnosed as the cause of nausea, supplementation can help. Correcting the deficiency allows the body to produce healthy red blood cells again, restoring proper oxygen flow to the gut and alleviating digestive symptoms over time.

Yes, certain medications, such as metformin and proton pump inhibitors (PPIs), are known to interfere with B12 absorption with long-term use. This can lead to a deficiency and associated symptoms like nausea.

Yes, some people may have a B12 deficiency without experiencing noticeable symptoms, particularly in the early stages. However, as the deficiency progresses, symptoms often develop gradually over time.

Yes, you should see a doctor for a proper diagnosis. A B12 deficiency can have serious long-term consequences if left untreated, and a healthcare professional can determine the cause and recommend the most effective treatment plan.