Oxidative stress — the imbalance between reactive oxygen species (ROS) and the body’s antioxidant defences — is implicated in ageing, inflammation, and the development of chronic disease. Antioxidant supplementation has long been positioned as a countermeasure, but the science is considerably more nuanced than the marketing suggests.
How Oxidative Stress Works
Free radicals are molecules with unpaired electrons that react indiscriminately with proteins, lipids, and DNA, causing structural damage that accumulates over time. The body maintains an endogenous antioxidant defence network — including superoxide dismutase (SOD), catalase, and glutathione peroxidase — that neutralises ROS under normal conditions. Excess ROS production from environmental exposures (UV radiation, air pollution, cigarette smoke), metabolic stress, intense exercise, or infection can overwhelm this system.
The consequence of chronic oxidative stress at the cellular level includes mitochondrial dysfunction, accelerated telomere shortening, protein aggregation, and lipid peroxidation of cell membranes. These processes are mechanistically linked to cardiovascular disease, neurodegeneration, type 2 diabetes, and skin ageing — which is why antioxidant interventions attract such interest across wellness and medical nutrition alike.
Key Antioxidant Nutrients and Their Evidence Base
Vitamin C (ascorbic acid) and vitamin E (tocopherols) are the best-established dietary antioxidants with the strongest EU-authorised health claims. Vitamin C contributes to the protection of cells from oxidative stress and to normal collagen synthesis. Vitamin E contributes to the protection of cell constituents from oxidative damage. Both claims are EU-registered under Regulation (EC) No 1924/2006 with established daily intake thresholds.
Selenium and zinc are trace elements that function as cofactors for endogenous antioxidant enzymes rather than as direct radical scavengers. Selenium is a component of glutathione peroxidase; zinc is required for SOD activity. Both carry EU-authorised claims for protection of cells from oxidative stress at specific daily doses.
Polyphenolic antioxidants — including resveratrol, quercetin, and anthocyanins — are widely marketed but lack EU-authorised health claims. Their in vitro antioxidant activity is well established, but translating this to in vivo human benefit is complicated by bioavailability limitations and the complex redox biology of living systems.
The Antioxidant Paradox
It is important to note that ROS are not uniformly harmful. At physiological levels, they serve as signalling molecules involved in cellular adaptation, immune function, and exercise-induced hormesis. High-dose antioxidant supplementation has in some contexts been shown to blunt beneficial adaptations — notably, antioxidant supplementation during exercise training may impair mitochondrial biogenesis and reduce the training-induced improvement in insulin sensitivity.
This does not invalidate antioxidant supplementation broadly, but it does support a nuanced, targeted approach — addressing specific deficiencies or high-risk exposures rather than blanket high-dose supplementation. Supplement brands should ensure their messaging reflects the current evidence and remains within the bounds of authorised claims.
