The oxygen in the air we breathe is transferred from the lungs into the blood and carried to every cell in the body. Once inside a cell, it helps fire many reactions including the burning of energy, a process known as 'oxidation'.
During oxidation, substances known as free radicals are formed. Chemically, these are unstable because they lack an electron; they literally go charging off round the body in search of one to regain stability. The trouble is they're not choosy and will grab one from the nearest source. This could be from a cell wall or some material inside a cell. The unsuspecting donor which gives up an electron is left damaged. It's thought that such damage to genetic material could cause cancer.
As well as being formed as a natural by-product of living, car exhaust fumes, cigarette smoke and UV light can also increase free radicals.
But our bodies have developed a defence system against them in the form of 'antioxidants'. Antioxidants are able to give up one of their own electrons with no detrimental consequences to themselves. Some of the most important are in food and drink. Vitamins C, E and betacarotene are the best known and are found in fruits and vegetables. Recent research shows that substances such as the green pigment, luteolin, in spinach; lycopene, the red pigment in tomatoes; and polyphenols in tea, red wine and apples also have strong antioxidant effects and may help protect against disease.