What is oxidative stress?

Oxidative stress is an imbalance between reactive molecules, often called free radicals, and the body's ability to neutralise them. A little is normal and even useful. Too much, for too long, can damage cells and is involved in many chronic diseases.

Choose Detailed for the fuller picture, or Scientific for mechanisms and study data.

Every cell makes reactive oxygen molecules as it produces energy. The body keeps them in check with its own antioxidant systems, led by glutathione, and with antioxidants from food such as vitamins C and E.

When the balance tips

Smoking, alcohol, pollution, high blood sugar and excess body fat all increase the load of reactive molecules. Over time this can damage fats, proteins and DNA.

Do antioxidant supplements help?

The evidence is mixed. Some targeted uses have shown benefit, such as vitamin E in a specific form of fatty liver disease. But large trials of antioxidant supplements in healthy people have generally not prevented disease, and some high-dose supplements have caused harm.

The best antioxidants

A diet rich in vegetables, fruit, pulses and whole grains, not smoking and staying active.

Reactive oxygen and nitrogen species act as signalling molecules at physiological concentrations (redox signalling). Pathology arises when production exceeds the capacity of enzymatic (superoxide dismutase, catalase, glutathione peroxidase) and non-enzymatic defences. Hormesis may explain why indiscriminate antioxidant supplementation can blunt adaptive responses, for example to exercise.