Oxidative Stress Explained: Free Radicals, Antioxidants and Your Diet

Cells make energy using oxygen. A small fraction of that oxygen forms reactive molecules such as superoxide and hydrogen peroxide. Biochemists now describe a healthy middle range — 'oxidative eustress' — where these molecules help regulate cell growth and immune defence, and a harmful excess called oxidative distress, where they damage cell membranes, proteins and DNA. Managing this balance is a core idea in cellular nutrition.

Common drivers include:

Oxidative stress does not have specific symptoms of its own and there is no single routine test for it. It is a process that contributes to conditions such as diabetic complications, atherosclerosis and age-related eye and nerve changes. Claims that a home kit or symptom checklist can 'diagnose' oxidative stress should be treated with scepticism.

The body's main antioxidant defences are its own enzymes — superoxide dismutase, catalase and glutathione peroxidase — and molecules such as glutathione. These depend on zinc, copper, manganese, selenium and adequate protein. Dietary antioxidants such as vitamin C, vitamin E and plant polyphenols play a supporting role.

Diets high in vegetables and fruit are consistently linked with better health outcomes, even if no single antioxidant explains why.

A Cochrane review of randomised trials found that beta-carotene, vitamin E and high-dose vitamin A supplements did not reduce mortality and may increase it. Because low levels of reactive oxygen species are useful signals, flooding cells with antioxidants may blunt normal adaptations. Read more in cellular nutrition vs supplements.

Stop smoking, keep blood sugar in range, move daily, sleep well, reduce alcohol and fill half your plate with vegetables and fruit. If you have diabetes, heart disease or a chronic condition, these steps are best tailored with your doctor — see our diabetology consults.