Antioxidants act as 'free radical scavengers' and thus help to prevent and repair damage done by free radicals.  Free radicals are a natural product of the body, created when cells use oxygen.  Antioxidants are therefore essential to keep the levels of free radicals in check and are known to prevent problems caused by oxidative damage, such as heart disease, cancer.  Antioxidants also help to slow the ageing process.