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Antioxidants

WHAT ARE ANTIOXIDANTS?

Antioxidants include the vitamins A, C and E, and yellow-coloured carotenoids, such as beta-carotene. Antioxidants help to counter the detrimental effects of oxygen free radicals which form naturally during normal metabolism, and by external factors such as x-rays, ultra-violet radiation and pollution. Oxygen free radicals have been implicated in the development of several diseases including cancer and heart disease, highlighting the need to consider antioxidant levels as part of preventative medicine.

WHERE WILL I FIND ANTIOXIDANTS?

There are a number of naturally occurring substances in food, such as vitamins and phenolic compounds which are large molecules comprised of a number of ring structures which have antioxidant properties. It is also possible to purchase antioxidant vitamin supplement tablets (containing vitamins E & C, and beta-carotene).

WHAT ARE THE BENEFITS OF ANTIOXIDANTS?

Recent research has estimated that the risk of cancer and heart disease is considerably lower in people who consume 5-7 serves of antioxidant-rich fruit and vegetables. Other studies have shown that after three months the level of protection against heart disease provided by a vitamin supplement was 27% better than normal; after six months the level of protection had risen to 35% better than normal.

It has been proposed that extra health benefits may derive from above-average intake of these compounds. This is supported by the extensive medical studies which indicate that diets high in antioxidant rich foods, such as fruit and vegetables, offer significant protection against general degenerative diseases.

More research is needed however, to substantiate this further, and to also consider the importance of non-nutrient antioxidants in the diet, as well as other protective plant substances in foods which may not be antioxidants. At present it appears that the wide mix of antioxidants obtained from plant foods work more effectively in the body that single supplements with pure antioxidants in tablet form although these may be of value in some circumstances.

WHAT MORE DO WE NEED TO KNOW?

More information is needed concerning the relative antioxidant potencies of non-nutrient antioxidants and conventional antioxidants in food. We also need to know more about the distribution and function of antioxidants in cells in the body, and the potential to influence this distribution by dietary means.

Current research is evaluating the importance of lesser known antioxidants in plant foods as anti-cancer agents. Levels of intake of the known nutrient antioxidants needed to protect cells against naturally occurring and induced damage to genes (elements in the structure of our hereditary material), and the associated risks of cancer, also need to be established.

ANTIOXIDANTS AND CORONARY HEART DISEASE

Coronary heart disease (or ischaemic heart disease) results from blockages of the coronary arteries by atherosclerotic plaques which are essentially complex cholesterol deposits. Coronary heart disease has been extensively studied and the main risk factors for its development have been identified. These risk factors include: hyperlipidemia (high blood fats), obesity, hypertension, diabetes mellitus and lack of physical activity.

WHAT ARE ANTIOXIDANTS?

There have been some observational studies which indicate that antioxidants in the diet may have a protective effect on coronary heart disease. Antioxidants include the vitamins A, C and E, and beta-carotene. Antioxidants help to counter the detrimental effects of oxygen free radicals which form naturally during normal metabolism. Free radicals are thought to play a role in coronary heart disease, cancer and inflammatory conditions. At this stage, without a complete understanding of how free radicals work, large doses of antioxidants are not recommended. However eating a variety of foods which contain natural antioxidants, such as fruit, vegetables and wholegrain products may have a beneficial effect.

HOW MIGHT ANTIOXIDANTS HELP REDUCE CORONARY HEART DISEASE?

Antioxidants in food prevent oxygen from making the food rancid, or causing discolouration or loss of flavour. In the body antioxidants appear to work by preventing the “bad” LDL-cholesterol (Low Density Lipoprotein cholesterol) from being oxidised and producing “foam” cells which form fatty streaks in the walls of blood vessels. Eventually these produce atherosclerosis and arterial narrowing and an increased risk of angina, heart attacks and strokes.

Research has shown that the antioxidants beta-carotene and vitamin E are found in the core of the LDL particle and it is known that giving large doses of vitamin E can prevent oxidation in vitro and help in sexual dysfunction treatment . Therefore work on the role of antioxidants in preventing heart disease is being carried out in centres around the world, including Australia.

WHICH FOODS CONTAIN ANTIOXIDANTS?

Fruit, vegetables and wholegrain products contain antioxidants.

Vitamin C (milligrams per 100 grams of food)

 

  • Capsicum (231 mg)
  • Strawberries (58)
  • Blackcurrants (209)
  • Cabbage (56)
  • Broccoli, cooked (92)
  • Orange juice (49)
  • Brussels sprouts, cooked (83)
  • Mango (41)

 

Vitamin E (milligrams per 100 grams of food)

 

  • Sunflower oil (48.7 mg)
  • Wheatgerm (11.0)
  • Polyunsaturated margarine (25.0)
  • Tuna, canned (6.3)
  • Hazelnuts (21.0)
  • Peanuts (5.6)
  • Almonds (20.0)
  • Olive oil (5.1)

 

Beta-carotene

 

  • Found in deep yellow/orange vegetables and fruits and dark green leafy vegetables (eg. carrot, pumpkin, apricot, mango, spinach, broccoli, endive, turnip, tomato).

 

FUTURE RESEARCH

Although considerable evidence shows that high levels of antioxidant vitamins are associated with protection against LDL oxidation and cardiovascular disease, the only randomised trial performed to date has failed to show any benefit. A recent review * of research papers about antioxidants and their impact on heart disease risk has concluded that modest doses of antioxidants were used in most studies and that higher doses may be required to show clinical effects. Recommendations to take vitamin supplements should await positive evidence.