Can Atrophic Gastritis Cause Folate Deficiency?
Atrophic gastritis causes folate malabsorption but typically does not result in clinical folate deficiency because bacterial overgrowth in the hypochlorhydric stomach compensates by synthesizing folate. 1
Mechanism of Folate Malabsorption
- Atrophic gastritis destroys parietal cells, leading to hypochlorhydria or achlorhydria, which impairs folic acid absorption in the proximal small intestine 1
- When folic acid is administered with hydrochloric acid (0.1 N HCl), absorption improves significantly from 31% to 54% in patients with atrophic gastritis, demonstrating that the malabsorption is acid-dependent 1
- The elevated small intestinal pH (7.1 vs 6.7 in controls) and increased bacterial counts in atrophic gastritis patients create conditions for bacterial folate synthesis 1
Clinical Reality: Why Folate Deficiency Rarely Occurs
- Despite documented folate malabsorption, serum folate levels remain normal in patients with atrophic gastritis because intestinal bacteria synthesize folate in the hypochlorhydric environment 1
- Studies show that bacteria cultured from small intestinal aspirates of atrophic gastritis patients can synthesize folate in vitro when incubated in folate-free medium 1
- Paradoxically, patients with atrophic gastritis often have higher mean serum folate levels compared to controls, likely due to bacterial folate synthesis and accumulation of 5-methyl tetrahydrofolate secondary to vitamin B12 deficiency 2
Contrasting Evidence on Folate Levels
- One study in patients undergoing coronary arteriography found lower folate levels (6.2 vs 7.4 ng/ml) in H. pylori-positive patients with atrophic gastritis compared to controls, though this effect was described as "not strong" 3
- However, the predominant evidence shows normal or elevated folate levels in atrophic gastritis patients 1, 2
Clinically Relevant Deficiencies in Atrophic Gastritis
The micronutrient deficiencies that actually occur in atrophic gastritis are:
- Iron deficiency - occurs in up to 50% of patients with corpus-predominant disease and presents much earlier than vitamin B12 deficiency 4
- Vitamin B12 deficiency - develops due to reduced gastric acid and loss of intrinsic factor from parietal cell destruction 4
- Vitamin D deficiency - the most common deficiency, found in 76 of 122 patients (62%) in one observational study 5
- Calcium deficiency - impaired due to reduced calcium salt dissolution in the hypochlorhydric environment 6
Important Clinical Pitfall
- Do not confuse folate malabsorption (which occurs) with folate deficiency (which typically does not occur clinically) - the compensatory bacterial synthesis mechanism prevents clinical deficiency despite impaired absorption 1
- When evaluating patients with atrophic gastritis, focus screening efforts on iron, vitamin B12, vitamin D, and calcium rather than folate 6, 4