Does zinc support antioxidant defenses and endothelial repair while deficiency increases oxidative stress and impairs nitric oxide-dependent endothelial function?

Zinc has a credible role in redox biology, but the vascular-repair and nitric-oxide portions of the claim remain more mechanistically supported than clinically demonstrated.

Antioxidant and oxidative-stress evidence

• Controlled-trial evidence indicates selective—not universal—effects on antioxidant systems. A 2021 meta-analysis of 23 controlled trials found higher glutathione and total antioxidant capacity with zinc; superoxide dismutase (SOD) improved after adjustment for publication bias, while glutathione peroxidase (GPx) did not significantly change overall.
• In older adults, six months of zinc increased Cu/Zn-SOD activity, although another study reported concurrent decreases in GPx and catalase. Thus, zinc modulates antioxidant enzymes rather than reliably increasing every antioxidant defense.
• A meta-analysis of 25 adult trials found lower malondialdehyde and higher total antioxidant capacity with supplementation. A six-month placebo-controlled older-adult trial using 45 mg/day elemental zinc similarly lowered lipid-peroxidation and inflammatory biomarkers. These are biochemical effects, not proof of fewer vascular events.

Endothelial mechanisms

• Zinc depletion can increase NADPH-oxidase- and NOS-derived reactive species. Peroxynitrite can disrupt the eNOS zinc–thiolate cluster, promoting eNOS uncoupling: eNOS then generates superoxide rather than nitric oxide, potentially amplifying oxidative stress and reducing nitric-oxide bioavailability.
• In endothelial cells, zinc protected against hydrogen-peroxide injury through Nrf2-dependent induction of GCLC and glutathione synthesis. Extracellular Zn²⁺ also activates the zinc-sensing receptor GPR39, influencing endothelial survival, growth, and vascular signaling.
• A placebo-controlled trial found lower circulating VCAM-1 with zinc, consistent with reduced endothelial activation, but did not establish improved re-endothelialization or direct endothelial function.

Clinical interpretation

• Human studies have not demonstrated improved flow-mediated dilation, nitric-oxide-dependent vascular function, or clinical endothelial repair with zinc supplementation. Low circulating zinc also may reflect inflammation-related redistribution rather than true deficiency.

Bottom line

• Zinc deficiency is well supported as a contributor to oxidative stress; zinc’s antioxidant-enzyme effects are selective. The proposed consequences for endothelial repair and nitric-oxide-dependent endothelial function are biologically plausible, but remain unproven as direct clinical benefits of supplementation.