Antioxidants and oxidative stress

Written by Dr Dan Rutherford, GP

What is oxidative stress?
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.

Antioxidants
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.

Foods and antioxidants

Tomatoes 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.

Citrus fruits
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.

Tea
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.

Carrots
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).

Beta-carotene is an antioxidant that has been much discussed in connection with lung cancer rates. The evidence is conflicting, with one study showing an increase in risk, but further research is being done to see if it has a protective effect.

Will eating antioxidants really protect me from disease?
Studies have shown that people who eat a diet that is rich in fruit and vegetables are less likely to get diseases such as cancer, heart disease and stroke.

It has not yet been proven that antioxidants alone are responsible for this drop in risk.

For example, the research that has been done on the effect of diet on cancer has been difficult to conduct and interpret.

Even so, there is now a good body of evidence to indicate the protective effect of fruit and vegetables on many common cancers, including those of colon, breast and bladder.

Other articles on antioxidants

• Fruit and vegetables
• Antioxidants - tips for healthy living

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