Does low stomach acid reduce non-heme iron absorption?

Gastric acidity plays an essential role in systemic iron homeostasis by preparing dietary non-heme iron for absorption. Without adequate stomach acid, the body cannot efficiently process or absorb this vital nutrient.

Mechanistic pathway of iron preparation

• Gastric pH and Solubility: A highly acidic gastric environment (pH < 2.0) is required to liberate ferric iron ($\text{Fe}^{3+}$) from the dietary matrix, preventing it from aggregating into insoluble complexes or precipitating at a neutral pH.
• Reduction and Enterocyte Transport: Non-heme iron must be in its soluble, reduced ferrous ($\text{Fe}^{2+}$) state to cross the apical membrane of duodenal enterocytes via divalent metal transporter 1 (DMT1). Although apical ferrireductases like duodenal cytochrome b (Dcytb) assist in converting $\text{Fe}^{3+}$ to $\text{Fe}^{2+}$, this enzymatic pathway is highly dependent on preceding acidic solubilization.
• Impact of Hypochlorhydria: Elevated gastric pH—commonly caused by chronic proton pump inhibitor (PPI) therapy or atrophic gastritis—prevents iron dissolution and promotes binding to dietary inhibitors like phytates and polyphenols, sharply reducing the pool of bioavailable iron.

Clinical implications and interventions

• Iron Deficiency Risk: Prolonged suppression of gastric acid directly restricts the quantity of soluble ferrous iron reaching the duodenum, significantly increasing the long-term risk of iron deficiency and microcytic anemia.
• Mitigation via Vitamin C: Co-administration of ascorbic acid (Vitamin C) can bypass some limitations of hypochlorhydria. Vitamin C acts as a potent electron donor, chemically reducing $\text{Fe}^{3+}$ to $\text{Fe}^{2+}$ and chelating the iron to maintain its solubility even as it transitions into the more alkaline duodenal lumen.

Bottom line

• Gastric acid is a vital physiological prerequisite for non-heme iron absorption. Hypochlorhydria impairs the upstream solubilization and reduction of iron, limiting duodenal transport via DMT1, though co-administration of Vitamin C can clinically mitigate this impairment.