Understanding the Link: What Vitamin Deficiency Causes Achlorhydria?

October 23, 2025 •

4 min read

While the question asks what vitamin deficiency causes achlorhydria, it is often the reverse: the underlying condition causing achlorhydria leads to a vitamin deficiency. An estimated 15–25% of vitamin B12 deficiency in older adults is related to autoimmune atrophic gastritis, which also causes achlorhydria.

Quick Summary

This article explores the complex relationship between achlorhydria and nutritional deficiencies. It explains how autoimmune atrophic gastritis and pernicious anemia lead to both the lack of stomach acid and poor vitamin B12 absorption. The article details the critical role of intrinsic factor and parietal cells, highlighting other nutrients impacted by low stomach acid. It also discusses risk factors and modern management strategies.

Key Points

Pernicious Anemia: The most common autoimmune cause of achlorhydria, it leads to a severe vitamin B12 malabsorption due to the destruction of gastric parietal cells.
Not Cause, but Consequence: Vitamin B12 deficiency does not cause achlorhydria; rather, the underlying condition responsible for achlorhydria, like autoimmune gastritis, leads to the deficiency.
Intrinsic Factor: Parietal cell destruction also eliminates intrinsic factor, a protein vital for absorbing vitamin B12.
Impact on Other Nutrients: The low acid environment of achlorhydria also impairs the absorption of essential nutrients like iron, calcium, and vitamin C.
Other Causes: Beyond autoimmune issues, other causes of achlorhydria that can lead to B12 deficiency include H. pylori infection, stomach surgery, and long-term use of proton pump inhibitors (PPIs).
Lifelong Management: In cases of irreversible autoimmune damage, lifelong vitamin B12 supplementation, often via injection, is required.
Underlying Cause: Effective management involves identifying and addressing the root cause of the achlorhydria, which may include eradicating bacterial infections.

Achlorhydria is a medical condition characterized by the complete absence of hydrochloric acid (HCl) in the stomach, while hypochlorhydria describes a reduction in its production. Gastric acid is crucial for proper digestion, including breaking down proteins and activating digestive enzymes. Its absence can set off a cascade of nutritional problems, most famously a deficiency in vitamin B12.

The Autoimmune Link: Pernicious Anemia and Vitamin B12

The most prominent and well-documented connection between a disease process that causes achlorhydria and a subsequent vitamin deficiency is pernicious anemia. This is an autoimmune disorder where the body's immune system mistakenly attacks its own tissues in the stomach lining. Specifically, it targets the parietal cells, which have two vital functions:

Producing hydrochloric acid (HCl).
Secreting intrinsic factor (IF), a protein necessary for vitamin B12 absorption.

When parietal cells are destroyed through autoimmune atrophic gastritis, the dual loss of HCl (causing achlorhydria) and intrinsic factor creates a severe malabsorption issue for vitamin B12. Vitamin B12, or cobalamin, is crucial for DNA synthesis, red blood cell formation, and proper neurological function.

The B12 Absorption Process in Detail

Release from food: In a healthy stomach, the acidic environment releases vitamin B12 from food proteins.
Binding to IF: The free B12 then binds with intrinsic factor, forming a complex.
Absorption in the ileum: This B12-IF complex travels to the terminal ileum (the last part of the small intestine), where it is absorbed.

In someone with pernicious anemia, achlorhydria prevents the initial release of B12 from food, and the lack of intrinsic factor prevents its absorption later on. This leads to a severe, progressive vitamin B12 deficiency, which can cause megaloblastic anemia and neurological damage if left untreated.

Achlorhydria and Other Nutritional Deficiencies

Beyond vitamin B12, achlorhydria can impair the absorption of other key nutrients. The low acid environment of the stomach disrupts several processes required for optimal nutrient uptake, leading to a host of secondary deficiencies.

Iron: Stomach acid is essential for converting dietary iron into a form that can be absorbed by the body. Achlorhydric patients frequently develop iron deficiency anemia.
Calcium and Vitamin D: Adequate stomach acid aids in the absorption of calcium. While the exact mechanism is less understood, low stomach acid can lead to lower calcium and vitamin D levels, potentially contributing to weakened bones.
Vitamin C: Research has shown that vitamin C is less stable in an alkaline environment, and the lack of stomach acid (which is acidic) leads to its degradation. This can exacerbate or contribute to a vitamin C deficiency.

A Comparison of Achlorhydria Causes and Nutritional Impact


Feature	Autoimmune Atrophic Gastritis / Pernicious Anemia	H. pylori Infection	Long-Term Proton Pump Inhibitor (PPI) Use
Mechanism	Autoimmune destruction of parietal cells, leading to a permanent loss of HCl and intrinsic factor.	Chronic infection that leads to inflammation and destruction of the gastric mucosa over time, causing decreased acid secretion.	Suppression of proton pumps in parietal cells, which are responsible for secreting stomach acid.
B12 Deficiency	Primary Cause: Inadequate production of intrinsic factor prevents B12 absorption. Deficiency is severe and often requires injections.	Secondary: Can contribute to B12 deficiency, often due to associated atrophic gastritis and bacterial overgrowth.	Secondary: Long-term use reduces stomach acid needed to release food-bound B12, leading to deficiency over time.
Iron Deficiency	High Risk: Achlorhydria significantly impairs the absorption of dietary iron, often leading to anemia.	Elevated Risk: Malabsorption due to low acid combined with the potential for bleeding from infection can cause iron deficiency.	Potential Risk: The reduction in stomach acid can decrease iron absorption, particularly non-heme iron.
Reversibility	Irreversible. Lifelong vitamin B12 supplementation is necessary, but the anemia can be reversed.	Potentially reversible with successful H. pylori eradication therapy, though acid secretion may not fully return.	Potentially reversible by reducing or discontinuing the PPI, under medical supervision.

Managing Nutritional Deficiencies in Achlorhydria

Management of achlorhydria-related nutrient deficiencies primarily involves addressing the root cause and providing targeted supplementation. For example, in pernicious anemia, parenteral (injection) or high-dose oral vitamin B12 supplementation is necessary for life. Treating H. pylori infection with antibiotics can sometimes help restore some acid production. Individuals on long-term PPIs may have their dose adjusted or medication changed.

Dietary and Lifestyle Considerations

Supplementation: Oral supplements of iron, calcium, and other vitamins may be needed to correct secondary deficiencies.
Digestive Support: In some cases, hydrochloric acid supplements combined with pepsin may be used to aid digestion, though this should always be done under the guidance of a healthcare professional.
Food Choices: Focusing on nutrient-dense foods and, in some cases, fortifying the diet can help. Vegans should be especially vigilant about B12 intake.
Meal Habits: Eating smaller, more frequent meals and chewing food thoroughly can help improve digestion.

Conclusion

While vitamin B12 deficiency is a significant nutritional problem associated with achlorhydria, it does not cause the condition directly. Instead, a shared underlying pathology, such as autoimmune atrophic gastritis (which causes pernicious anemia), leads to both the lack of stomach acid and the inability to absorb B12. Other issues like H. pylori infection and long-term medication use can also lead to achlorhydria and subsequent nutrient deficiencies, including iron and calcium. Effective management requires accurate diagnosis of the underlying cause and appropriate, often lifelong, supplementation to prevent serious complications.

Authoritative Source: Vitamin B12 Deficiency - StatPearls - NCBI Bookshelf

Frequently Asked Questions

Achlorhydria is the complete absence of hydrochloric acid in the stomach. Its primary cause can be autoimmune atrophic gastritis, where the immune system destroys acid-producing parietal cells.

Achlorhydria resulting from autoimmune gastritis destroys parietal cells, which produce both stomach acid and intrinsic factor. Without intrinsic factor, the body cannot absorb vitamin B12 from food, leading to a deficiency.

No, while pernicious anemia is a significant cause via autoimmune gastritis, other factors can lead to achlorhydria. These include H. pylori infection, stomach surgery, and long-term use of proton pump inhibitors (PPIs).

The low acid environment impairs the absorption of several nutrients, including iron, calcium, vitamin C, and other B vitamins.

The reversibility depends on the cause. Achlorhydria from autoimmune gastritis is typically permanent. In cases of H. pylori infection or long-term PPI use, it may be partially or fully reversible upon treatment or medication adjustment.

Treatment usually involves intramuscular injections of vitamin B12 to bypass the impaired absorption pathway. High-dose oral B12 may also be an option for some individuals.

Long-term risks include severe nutritional deficiencies (especially vitamin B12 and iron), neurological complications from B12 deficiency, and an increased risk for gastric cancer.

No, PPI-induced achlorhydria or hypochlorhydria is usually not permanent. It can be treated by reducing the dose or withdrawing the medication under a doctor's supervision.