'Rich in antioxidants" is an advertiser's dream slogan. It ensures food and drinks are snapped up in the hope of preventing ageing, cancer or heart disease. Last year, 22 million of us took a supplement and 13% of supplements sold in the UK boasted on the label that they contained antioxidants. Antioxidants, such as vitamins A, C and E, are marketed as good for our health but what is the evidence?
The antioxidant story started more than 40 years ago when scientists discovered that chemicals called Reactive Oxygen Species (ROS) react with components of our cells causing damage, sometimes irreversible. This process is called oxidative stress. ROS refer to any chemical that damages the cell by causing this stress. The "damaging free radicals" you hear about are one kind. Unfortunately, ROS are not avoidable; they are chemicals continually produced within our cells that generate the energy we need to stay alive. So cells also contain a battery of defences to protect us against oxidative stress.
Our cells run into trouble when these defences are overwhelmed, for example when we encounter large amounts of ROS; then oxidative stress is associated with heart disease, cancer and ageing. These insurmountable quantities of ROS may be from the environment, for example from cigarette smoke, or pollution, or they may be produced by our own bodies when we're sick.
Recognition that ROS cause disease was the first step towards our fascination with antioxidants; the substances that mop up ROS. Barry Halliwell, a professor of biochemistry at Singapore University and a world expert in free radicals, says that when research started in the mid-1990s it showed "diets rich in plants were associated with lower risk of developing many age-related diseases and most people would have better health if they ate more fruits and vegetables". Plants contain large amounts of antioxidants to protect them against the ROS they produce during photosynthesis, so scientists concluded fruit and veg were beneficial for us because they contained antioxidants. After this, it was assumed that taking antioxidants in the form of vitamin pills would help prevent disease. "The assumption often was that free radicals cause diseases, and antioxidants will prevent and/or cure them," says Halliwell.