Can H. pylori–associated chronic gastritis reduce gastric acid and impair iron and vitamin B12 absorption?

Chronic Helicobacter pylori (H. pylori) infection is a well-established cause of gastritis that fundamentally alters gastric physiology. The impact of this infection depends largely on the pattern of inflammation; when the infection leads to corpus-predominant gastritis—inflammation of the main body of the stomach—it results in the progressive loss of acid-secreting cells and a subsequent cascade of nutrient malabsorption.

Clinical and effectiveness evidence

Extensive clinical evidence confirms that H. pylori infection is a significant risk factor for iron and vitamin B12 deficiencies.

• Iron Deficiency: Meta-analyses of randomized controlled trials demonstrate that patients with H. pylori have a 1.5 to 2.6 times higher risk of iron deficiency anemia (IDA) compared to uninfected individuals. Crucially, H. pylori eradication has been shown to significantly improve hemoglobin and serum ferritin levels, often resolving anemia that was previously resistant to oral iron supplementation.
• Vitamin B12 Deficiency: Systematic reviews indicate that H. pylori-positive patients consistently have lower serum vitamin B12 levels than negative controls. Large-scale studies have shown that successful eradication therapy significantly increases serum B12 concentrations, confirming the infection's role in impaired absorption.

Mechanistic explanations

The impairment of iron and B12 absorption stems from several convergent pathological pathways initiated by H. pylori-associated inflammation:

• Hypochlorhydria and Achlorhydria: The hallmark of corpus-predominant gastritis is the destruction and dysfunction of parietal cells. H. pylori and inflammatory cytokines (like IL-1β and TNF-α) directly inhibit the H+/K+-ATPase (proton pump) and eventually lead to glandular atrophy. This reduction in gastric acid is the primary driver of malabsorption.
• Iron Solubilization: Gastric acid is essential for converting dietary ferric iron (Fe3+) into the more soluble and absorbable ferrous form (Fe2+). Furthermore, H. pylori infection reduces levels of gastric ascorbic acid (vitamin C), which is a critical facilitator of non-heme iron absorption.
• Food-Cobalamin Malabsorption: Vitamin B12 is naturally bound to dietary proteins. Its absorption requires gastric acid and the enzyme pepsin (which also decreases during gastritis) to liberate the vitamin from these proteins. Without sufficient acid, B12 remains protein-bound and cannot bind to intrinsic factor for transport in the small intestine.
• Systemic Inflammation: Chronic infection increases systemic hepcidin levels, a hormone that regulates iron homeostasis. Elevated hepcidin sequesters iron within storage cells (macrophages), further reducing the iron available for red blood cell production.

Bottom line

H. pylori–associated chronic gastritis is a scientifically supported cause of reduced gastric acid and impaired absorption of iron and vitamin B12. This occurs primarily through the loss of parietal cell function (hypochlorhydria) and the resulting inability to solubilize iron or release B12 from food proteins. Eradication of the bacteria is a critical clinical step in reversing these deficiencies and restoring normal nutrient absorption.