Without oxygen, you would die. Yet the very oxygen that is keeping us alive is also contributing to our death because oxygen is toxic. Inhaling oxygen naturally produces harmful free radicals as a consequence of normal metabolism. Free radicals are unstable molecules or fragments of molecules with electrons desperately seeking a partner. This makes them highly reactive as they seek a partner molecule. This can be destructive as the pairing can cause a chain reaction of damage.

There is now evidence that the harm caused by free radicals can accumulate and contribute to the aging process, diseases such as heart disease and cancer and other ageing problems such as cataracts and nervous disorders. The free radicals may cause damage to DNA molecules so that new body cells mutate and become cancer cells. Free radical damage to blood LDL-cholesterol can make the cholesterol far more damaging to your artery lining than previously realized. (Note: Free radicals are not always harmful. Phagocytes in the blood produce free radicals to kill disease-causing microbes). It may be possible in the future to limit oxygen damage to the body so we slow the aging process and live longer.

Fortunately, the human body has devised ways to minimize the toxic damage of free radicals by neutralizing them through a series of antioxidant enzymes (glutathione peroxidases, superoxide dismutases and catalase). Essential minerals like selenium, copper and zinc are part of the structure of these enzymes, thereby playing an important role in protecting against free radicals. Vitamin E, vitamin C and beta-carotene also have antioxidant properties. There has been a great deal of interest in the non-nutrient antioxidants known as carotenoids and polyphenols, of which there are over 8,000 compounds in nature!

The Answer to Free Radicals

One of your favorite pastimes could create a 10 to 20 fold increase in oxygen consumption and therefore a subsequent increase in free radical production. It’s called exercise and has evoked the idea of the "oxygen paradox," that is, exercise (proven to be good for you) increases the level of free radicals (proven to be bad for you).

Does the "bad" outweigh the "good?" The answer is "No." Research strongly suggests that regular exercisers have a much higher level of their natural antioxidant enzymes to help protect against the free radicals produced in exercise. This has led to the theory that it is the weekend warrior who most requires antioxidant supplements as his or her antioxidant enzyme levels will be lower than someone who exercises regularly throughout the week. It should be noted that regular exercise reduces your risk of heart disease and overweight.

Vitamin E & C

A number of studies have shown a decrease in free radical damage when taking vitamin E and vitamin C supplements by physically active people, but there also is contradictory data that shows no benefit from taking these vitamins as a supplement. Unfortunately, that is the way of science and it may be another 10 to 20 years before we can fine-tune the message regarding antioxidant supplements in athletes. The message may well be different depending upon whether the athlete is strength training, speed training or endurance training. At the moment, some scientists favor the supplement, while others see no value in promoting supplements to athlete. Despite the different views, both parties are unanimous in their belief that athletes need to eat plenty of fruits and vegetables to get extra antioxidants.

I don’t know of any researcher who has tried to determine the amount of supplement needed, nor do I know of one whom has said how much exercise warrants a supplement. As suggested, the regular exerciser is least likely to need a supplement when training, but anyone involved in hard training or competition for 10 hours or more a week should give it some thought. A daily supplement of 10 to 15 mg alpha-tocopherol equivalents (vitamin E) covers the daily intake recommended by most countries and may be a useful adjunct to your normal diet that, for many people, provides only eight to 10 mg daily. Vitamin E appears safe at doses of 200 mg or less daily. Vitamin C is abundant in fruit, fruit juice and vegetables, but a supplement of 100 to 200 mg daily is unlikely to cause a problem.

Although healthy eating and/or a supplement may reduce oxidative stress, there is no evidence that this will also improve sports performance.

Food vs Supplements

When it comes to overall health, there is the oft-asked question: "Can I get all my antioxidants from food, or should I take a supplement?" While being a perfectly legitimate question, there doesn’t appear to be a simple answer.

If you are hoping to prevent illness and slow down ageing then, in the words of Dr Dorothy Mackerras, University of Queensland, Australia: "At present, it seems that bets can be better hedged by eating a greater quantity and variety of fruits and vegetables than by relying on high doses of a few compounds".

Dr Ross Bury, Therapeutic Goods Unit, Victoria, Australia believes "taking an antioxidant supplement is not equivalent to eating a balanced diet, rich in fruit and vegetables, which contains hundreds of different compounds in combination, including numerous antioxidants".

A thorough review of the scientific evidence unfortunately concluded that there were no specific antioxidants that helped to cure heart disease or cancer. Even the Heart Foundation is reluctant to recommend a supplement to avoid heart disease. Having said that, a lot of research still being performed and in the near future there may well be a breakthrough.

If you prefer to get your antioxidants through good eating then, as a guide, you will need to eat at least two fruit serves a day (about 300 g) and at least two to three metric cups of vegetables a day (about 400g). This is not a lot of food and should be a simple task for any healthy, active adult. It is unfortunate that only one in 10 adults are eating that much today.

Good Sources of Antioxidants

• Vitamin E – Vegetables, fruits, nuts, vegetable oils, wheat germ, oily fish
• Vitamin C – Fruits, vegetables
• Carotenoids – Yellow-orange fruits and vegetables, dark green vegetables, tomatoes, fruit and vegetable juices

References:

1. Kanter M. Free radicals, exercise and antioxidant supplementation. Proc Nut Soc 1998; 57: 9-13
2. Clarkson P. Anti-oxidants and physical performance. Critical Reviews in Food Sc & Nut 1995; 35: 131-141
3. Dekkers JC, van Doornen LJP, Kemper CG. The role of antioxidant vitamins and enzymes in the prevention of exercise-induced muscle damage. Sports Med 1996; 21: 213-238
4. Mackerras D. Antioxidants and health. Food Australia 1995; 47 (suppl): S3-S23
5. Bury R. Clinical applications of antioxidant nutrients. 1996 Public Health Division. Victorian Government Dept Human Services.