Vitamins such as C, E and beta-carotene (a precursor of vitamin A) as well as the mineral selenium have anti-oxidant properties. This means that they protect weak proteins and lipids in the cell membranes and play an important role in intercepting highly reactive oxygen atoms (“free radicals”). They scavenge free radicals, which are molecules with one or more unpaired electrons. They react rapidly with other molecules, starting chain reactions in a process called oxidation. Free radicals are a normal product of metabolism and the body produces its own antioxidants to keep them in balance. However, stress, ageing and environmental sources such as polluted air and cigarette smoke can add to the number of free radicals in the body, creating an imbalance. The highly reactive free radicals can damage healthy DNA and have been linked to changes that accompany ageing (such as age-related macular degeneration, a leading cause of blindness in older people) and with disease processes that lead to cancer, heart disease, and stroke.

Studies have suggested that the natural antioxidants in fresh fruits and vegetables have a protective effect. For example, vitamin E and beta-carotene appear to protect cell membranes; vitamin C removes free radicals from inside the cell.