Do vitamin C and plant polyphenols support antioxidant defenses by scavenging ROS and regenerating other antioxidants?

The original claim that vitamin C and plant polyphenols support antioxidant defenses by scavenging reactive oxygen species (ROS) and regenerating other antioxidants is strongly supported by scientific evidence. These molecules operate via synergistic, distinct chemical and biological pathways to reinforce cellular defenses.

Clinical and effectiveness evidence

• Biomarker improvements: Clinical interventions utilizing vitamin C (e.g., 500 mg twice daily) demonstrate significant reductions in sensitive markers of lipid peroxidation, such as urinary 4-hydroperoxy-2-nonenal (HPNE)-derived metabolites, particularly in cohorts with elevated baseline oxidative stress.
• Polyphenol-rich diets: Meta-analyses of clinical trials featuring polyphenol-rich interventions (such as almonds, berries, and grapes) show consistent increases in superoxide dismutase (SOD) activity and total antioxidant capacity, paired with reductions in key markers of oxidative DNA damage like 8-hydroxy-2'-deoxyguanosine (8-OHdG) and malondialdehyde.

Mechanistic explanations

• Vitamin C scavenging: Vitamin C (ascorbate, $\text{AscH}^-$) acts as a premier aqueous-phase antioxidant. It transfers single electrons or undergoes peroxyl radical addition to neutralize peroxyl, hydroxyl, and superoxide radicals with rapid second-order kinetics ($10^4$ to $10^8 \text{ M}^{-1}\text{s}^{-1}$).
• Vitamin E regeneration: Vitamin C regenerates oxidized vitamin E ($\alpha$-tocopheroxyl radical) at the lipid-aqueous membrane interface. This thermodynamically favorable reaction ($10^5$ to $10^7 \text{ M}^{-1}\text{s}^{-1}$) restores active, lipophilic vitamin E, preventing it from acting as a pro-oxidant.
• Polyphenol dual-action: In vitro, plant polyphenols directly neutralize ROS via hydrogen atom transfer (HAT) and single-electron transfer (SET), alongside chelating transition metals to inhibit hydroxyl radical formation. In vivo, because of rapid metabolism, polyphenols act primarily as mild hormetic stressors that activate the Keap1/Nrf2/ARE pathway. This translocates Nrf2 to the cell nucleus, upregulating endogenous antioxidant enzymes (SOD, catalase, GPx, HO-1) and rate-limiting enzymes for glutathione (GSH) synthesis.

Bottom line

Vitamin C and plant polyphenols are highly effective partners in maintaining cellular redox balance. Vitamin C directly scavenges aqueous ROS and regenerates membrane-bound vitamin E, while polyphenols act both as direct radical scavengers and as biological triggers that upregulate endogenous antioxidant enzymes via the Nrf2 pathway.