The process of oxidation in the human body damages cell
membranes and other structures including cellular proteins,
lipids and DNA. When oxygen is metabolised, it creates 'free
radicals' which steal electrons from other molecules, causing
damage. The body can cope with some free radicals and needs
them to function effectively. However, an overload of free
radicals has been linked to certain diseases, including heart
disease, liver disease and some cancers. Oxidation can be
accelerated by stress, cigarette smoking, alcohol, sunlight,
pollution and other factors.
Antioxidants are found in
certain foods that neutralise free radicals. These include the
nutrient antioxidants, vitamins A, C and E, and the minerals
copper, zinc and selenium. Other dietary food compounds, such
as the phytochemicals in plants and zoochemicals from animal
products, are believed to have greater antioxidant effects
than either vitamins or minerals. These are called the
non-nutrient antioxidants and include phytochemicals, such as
lycopenes in tomatoes, and anthocyanins found in
The effect of free radicals
of the degenerative conditions caused by free radicals
The disease-fighting antioxidants
- Deterioration of the eye lens, which contributes to
- Inflammation of the joints (arthritis).
- Damage to nerve cells in the brain, which contributes to
conditions such as Parkinson's or Alzheimer's disease.
- Acceleration of the ageing process.
- Increased risk of coronary heart disease, since free
radicals encourage low density lipoprotein (LDL) cholesterol
to adhere to artery walls.
- Certain cancers, triggered by damaged cell
diet high in antioxidants may reduce the risk of many
diseases, including heart disease and certain cancers.
Antioxidants scavenge the free radicals from the body cells,
and prevent or reduce the damage caused by oxidation. The
protective effect of antioxidants continues to be studied
around the world. For instance, men who eat plenty of the
antioxidant lycopene (found in tomatoes) may be less likely
than other men to develop prostate cancer. Lutein, found in
spinach and corn, has been linked to a lower incidence of eye
lens degeneration and associated blindness in the elderly.
Flavonoids, such as the tea catechins found in green tea, are
believed to contribute to the low rates of heart disease in
Sources of antioxidants
of antioxidants include:
- Allium sulphur compounds - leeks, onions and
- Anthocyanins - eggplant, grapes and berries.
- Beta-carotene - pumpkin, mangoes, apricots,
carrots, spinach and parsley.
- Catechins - red wine and tea.
- Copper - seafood, lean meat, milk and nuts.
- Cryptoxanthins - red capsicum, pumpkin and
- Flavonoids - tea, green tea, citrus fruits, red
wine, onion and apples.
- Indoles - cruciferous vegetables such as
broccoli, cabbage and cauliflower.
- Isoflavonoids - soybeans, tofu, lentils, peas and
- Lignans - sesame seeds, bran, whole grains and
- Lutein - leafy greens like spinach, and corn.
- Lycopene - tomatoes, pink grapefruit and
- Manganese - seafood, lean meat, milk and nuts.
- Polyphenols - thyme and oregano.
- Selenium - seafood, offal, lean meat and whole
- Vitamin C - oranges, blackcurrants, kiwi fruit,
mangoes, broccoli, spinach, capsicum and strawberries.
- Vitamin E - vegetable oils (such as wheatgerm
oil), avocados, nuts, seeds and whole grains.
- Zinc - seafood, lean meat, milk and nuts.
- Zoochemicals - red meat, offal and fish. Also
derived from the plants animals eat.
Some studies suggest that antioxidants are
less effective when isolated from food and presented in tablet
form. For instance, vitamin A (beta-carotene) has been
associated with a reduced risk of certain cancers but an
increase in others, such as lung cancer in smokers, if vitamin
A is purified from foodstuffs.
A study examining the
effects of vitamin E found that it didn't offer the same
benefits when taken as a supplement. Also, antioxidant
minerals or vitamins can act as pro-oxidants or damaging
'oxidants' if they are consumed at levels significantly above
the recommended dietary intakes (RDI). A well-balanced diet,
which includes consuming antioxidants from whole foods is
best. If you insist on taking a supplement, seek supplements
that contain all nutrients at the level of the RDIs.
Research is divided
over whether or not antioxidant supplements offer the same
health benefits as antioxidants in foods. It is recommended
that people eat a wide variety of fresh fruits, vegetables,
whole grains, lean meats and dairy products every day. The
diet should include five daily serves of fruit and vegetables.
One serve is a medium-sized piece of fruit or a half-cup of
cooked vegetables. See your doctor or dietitian for
Where to get help
Things to remember
- The process of oxidation in the human body produces
chemicals called free radicals, which damage cell membranes
and other structures.
- Free radicals have been linked to a variety of diseases,
including heart disease and certain cancers.
- Antioxidants are compounds in foods that scavenge and
neutralise free radicals.
- Evidence suggests that antioxidant supplements don't
work as well as the naturally occurring antioxidants in
foods such as fruits and vegetables.
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