What is the Fenton reaction and why does it matter for iron supplements?

The Fenton reaction is a chemical process where free ferrous iron (Fe²⁺) reacts with hydrogen peroxide (H₂O₂) present in gastric tissue to generate hydroxyl radicals — one of the most reactive and destructive biological oxidants. In the context of iron supplementation, this reaction occurs when a ferrous sulphate tablet dissolves in the stomach, releasing Fe²⁺ ions that immediately catalyse the reaction. The resulting hydroxyl radicals attack gastric epithelial cells, causing oxidative damage. The reaction is catalytic — iron is not consumed, so a small amount of iron can generate a large quantity of damaging radicals.

Does iron supplementation cause NF-kB activation in the stomach?

Yes. The oxidative stress generated by the Fenton reaction activates NF-kB — the master inflammatory transcription factor — in gastric epithelial cells. NF-kB drives production of IL-8, TNF-α, and other pro-inflammatory cytokines that amplify the initial chemical insult into sustained mucosal inflammation. This is the same transcription factor that H. pylori activates — which is why iron side effects are dramatically worse in H. pylori-positive patients: two simultaneous NF-kB activation sources produce additive damage.

Can quercetin reduce iron-related gastric damage?

Yes — through two complementary mechanisms. First, quercetin chelates free Fe²⁺ ions in the gastric environment, reducing the substrate available for the Fenton reaction and therefore the quantity of hydroxyl radicals generated. Second, quercetin inhibits NF-kB through IκB stabilisation — preventing the inflammatory amplification of whatever oxidative damage does occur. These two mechanisms address the pathway at steps 1 and 5 respectively.

Why does the oxidative stress pathway matter more in H. pylori-positive patients?

H. pylori activates NF-kB through its own virulence mechanisms (CagA injection, LPS-TLR4 stimulation) independently of iron. In an H. pylori-positive patient taking iron, two separate NF-kB activation sources are operating simultaneously: the bacterial source and iron's oxidative stress source. The resulting inflammatory cascade is significantly more intense than either would produce alone. Additionally, H. pylori already suppresses EGFR/ERK repair — meaning the stomach's capacity to recover between doses is already compromised before iron begins its damage.

What interrupts the oxidative stress pathway from iron supplements?

Three intervention points: (1) Reducing free Fe²⁺ availability — switching to ferrous bisglycinate (chelation reduces free ion release) or taking with food (dilutes and buffers ion concentration). (2) Scavenging hydroxyl radicals before they attack cells — antioxidant flavonoids including quercetin and myricetin neutralise ROS downstream of the Fenton reaction. (3) Inhibiting NF-kB activation — quercetin's IκB stabilisation prevents the inflammatory amplification of whatever oxidative damage occurs. A fourth point — activating EGFR/ERK repair (glabridin) — doesn't interrupt the damage pathway but accelerates recovery.

How Iron Supplements Cause Gastric Irritation — The Oxidative Stress Pathway

62%

of tested Indians with gut symptoms carry H. pylori — their NF-kB is already activated

Iron's oxidative stress hits an already-inflamed system, compounding the pathway at its most destructive point. TumGard India Gut Health Report 2026, n=20,363.

The pathway, step by step

Dissolution in gastric fluid

Ferrous sulphate dissolves rapidly in gastric acid, dissociating into free ferrous ions (Fe²⁺) and sulphate. The speed of this dissolution determines how quickly free iron is available to react with the mucosal surface. Ferrous sulphate dissolves faster than chelated forms — maximising the concentration of free ions in the gastric environment.

Step 1

Free iron contacts the gastric mucosa

Free Fe²⁺ ions diffuse through the mucus layer and come into contact with the gastric epithelium. In a healthy stomach, the thick mucus gel absorbs much of this contact. In a thinned or inflamed mucosa, Fe²⁺ reaches the epithelial surface more directly and at higher concentrations.

Step 2

The Fenton Reaction: Fe²⁺ + H₂O₂ → Fe³⁺ + OH⁻ + OH•

Free iron reacts with hydrogen peroxide naturally present in gastric tissue to generate hydroxyl radicals (OH•) — one of the most reactive and destructive forms of reactive oxygen species in biological chemistry. The reaction is catalytic: iron is not consumed, so a small amount of iron can generate a large quantity of hydroxyl radicals.

Step 3 — The key reaction

Hydroxyl radicals attack epithelial cell membranes

Hydroxyl radicals initiate lipid peroxidation — chain reactions that progressively damage the lipid membranes of gastric epithelial cells. Cell membrane integrity is compromised. In mild cases this causes reversible irritation. In sustained or high-concentration exposure, it causes cell death and mucosal erosion.

Step 4

NF-kB activation and inflammatory amplification

The oxidative stress from hydroxyl radical damage activates NF-kB — a transcription factor that acts as a master switch for the inflammatory response. NF-kB drives the production of IL-8, TNF-α, and other pro-inflammatory cytokines. These recruit immune cells to the gastric mucosa, amplifying the initial chemical insult into a sustained inflammatory state. NF-kB also suppresses the EGFR/ERK repair pathway — preventing recovery between doses.

Step 5

Oxidative stress from free iron generates reactive oxygen species that activate NF-kB in gastric epithelial cells — triggering the same pro-inflammatory cytokine cascade that characterises H. pylori-driven gastritis. The two mechanisms share a common inflammatory amplifier.

Ye YN et al. · Journal of Ethnopharmacology · 2023 · PMID 36842733

Why this matters in the context of H. pylori

NF-kB is the same transcription factor that H. pylori activates through its own virulence mechanism — CagA protein injection into gastric epithelial cells and lipopolysaccharide stimulation of TLR4 receptors. When iron's oxidative stress activates NF-kB in a stomach already under H. pylori's NF-kB activation, the signals compound. The gastric inflammatory state is more severe than either source would produce alone. And the EGFR/ERK repair pathway is running at even lower capacity.

Two NF-kB sources in 62% of India's supplement-taking population

This is the biological explanation for why iron tablet side effects are dramatically worse in H. pylori-positive patients — not a coincidence of prevalence, but a convergence of mechanism. Both sources activate the same transcription factor. The downstream damage is additive. And the EGFR/ERK repair pathway — suppressed by both — cannot adequately compensate for either.

Where the pathway can be interrupted

The oxidative stress pathway is not inevitable. There are three points at which it can be interrupted, and each corresponds to a distinct intervention strategy:

Three intervention points

Intervention Point 1 — Reduce free Fe²⁺ availability: Switch to ferrous bisglycinate (chelation slows free ion release) or take with food (dilutes and buffers ion concentration in the gastric environment). This reduces Fenton reaction substrate before the reaction begins.

Intervention Point 2 — Scavenge hydroxyl radicals: Quercetin and myricetin act as antioxidant flavonoids that neutralise ROS before they reach significant concentrations in the gastric epithelium. This limits lipid peroxidation at step 4.

Intervention Point 3 — Inhibit NF-kB: Quercetin inhibits NF-kB through IκB stabilisation — preventing the inflammatory amplification of whatever oxidative damage does occur. This addresses step 5 and also reduces the H. pylori NF-kB contribution simultaneously.

What long-term support requires

Interrupting the damage pathway reduces ongoing harm. But cumulative mucosal damage that has already occurred requires active repair — not just damage prevention. This is where the EGFR/ERK activation pathway becomes critical. Glabridin (a licorice-derived flavonoid) directly activates EGFR/ERK signalling in gastric epithelial cells, stimulating goblet cell regeneration and mucus synthesis — the structural repair that rebuilds the protective layer that iron's oxidative damage has eroded.

References

Ye YN et al. Licorice flavonoids and gastric mucosal repair via EGFR/ERK pathway. Journal of Ethnopharmacology. 2023;302:115866. PMID 36842733. Documents glabridin's EGFR/ERK activation mechanism and its role in gastric mucosal repair — the positive intervention that reverses the damage described in this pathway.
Xiao ZP et al. Quercetin as inhibitor of H. pylori urease. European Journal of Medicinal Chemistry. 2006;41(4):476–82. PMID 16887239. Establishes quercetin's NF-kB inhibitory activity and H. pylori urease inhibition — two of the three intervention points in the iron oxidative stress pathway.
Crowe SE. Helicobacter pylori infection. New England Journal of Medicine. 2019;380:1158–1165. PMID 30699316. H. pylori NF-kB activation mechanism through CagA and LPS-TLR4 — the converging point with iron's oxidative NF-kB activation described in this article.
Merlin Annie Raj, RD. TumGard India Gut Health Report 2026. Hugg Beverages Pvt. Ltd. 2026. tumgard.com/india-gut-health-report-2026. Source of 62% H. pylori positivity in symptomatic tested Indians — the population whose NF-kB is already activated when they begin iron supplementation.

How our data compares

The convergence of iron's oxidative NF-kB pathway with H. pylori's bacterial NF-kB pathway in the same gastric epithelial cells is mechanistically described across multiple peer-reviewed sources but has not been directly studied in controlled trials on Indian iron-supplementing patients. The clinical implication — that H. pylori-positive patients experience worse iron side effects — is derived from the mechanism and is consistent with clinical observation, but direct clinical trial data on this specific interaction in the Indian context is limited.

How Iron Supplements Cause Gastric Irritation — The Oxidative Stress Pathway Explained