Your body constantly reacts with oxygen as you breathe and your cells produce energy. As a consequence of this activity, highly reactive molecules are produced known as free radicals.
Free radicals interact with other molecules within cells. This can cause oxidative damage to proteins, membranes and genes.
Oxidative damage has been implicated in the cause of many diseases such as cancer and Alzheimer's and has an impact on the body's aging process.
External factors such as pollution, sunlight and smoking also trigger the production of free radicals.
To counteract oxidative stress, the body produces an armoury of antioxidants to defend itself. It's the job of antioxidants to neutralise or 'mop up' free radicals that can harm our cells.
Your body's ability to produce antioxidants (its metabolic process) is controlled by your genetic makeup and influenced by your exposure to environmental factors such as diet and smoking.
Changes in our lifestyles, which include more environmental pollution and less quality in our diets, mean that we are exposed to more free radicals than ever before.
How much do I need?
Your body's internal production of antioxidants is not enough to neutralise all the free radicals.
You can help your body to defend itself by increasing your dietary intake of antioxidants.
Examples of food-based antioxidants-
Antioxidant supplements Studies have shown that antioxidants supplements do not replicate the action of antioxidants from food. More research is needed before, say, Vitamin C supplements can be advised to prevent cancer.
Vitamins: vitamin E, vitamin C and beta carotene.
Trace elements that are components of antioxidant enzymes such as selenium, copper, zinc, and manganese.
Non-nutrients such as ubiquinone (coenzyme Q) and phenolic compounds such as phytoestrogens, flavonoids, phenolic acids and butylated hydroxytoluene (BHT), which is used as a food preservative.
Foods and antioxidants-
Tomatoes contain a pigment called lycopene that is responsible for their red colour but is also a powerful antioxidant.
Tomatoes in all their forms are a major source of lycopene, including tomato products like canned tomatoes, tomato soup, tomato juice and even ketchup.
Lycopene is also highly concentrated in watermelon.
Oranges, grapefruit, lemons and limes possess many natural substances that appear to be important in disease protection, such as carotenoids, flavonoids, terpenes, limonoids and coumarins.
Together these phytochemicals act more powerfully than if they were given separately.
It's always better to eat the fruit whole in its natural form, because some of the potency is lost when the juice is extracted.
Black tea, green tea and oolong teas have antioxidant properties. All three varieties come from the plant Camellia sinenis.
Common brands of black tea do contain antioxidants, but by far the most potent source is green tea (jasmine tea) which contains the antioxidant catechin.
Black tea has only 10 per cent as many antioxidants as green tea.
Oolong tea has 40 per cent as many antioxidants as green tea.
This because some of the catechins are destroyed when green tea is processed (baked and fermented) to make black tea.
Beta-carotene is an orange pigment that was isolated from carrots 150 years ago.
It is found concentrated in deep orange and green vegetables (the green chlorophyll covers up the orange pigment).