Most readers are aware of the research on oxidation, the use of oxygen by cells, which produce molecules called free radicals that carry an extra electron. These free radicals can damage cells until they are neutralized by anti-oxidants. The fear has been that when a person exercises, they produce 10 to 20 times the amount of free radicals compared to resting status, which would mean there are a lot more free radicals to damage the body's cells.
Now, if anyone reading this actually believed this theory, they would not be reading this since they would not be doing triathlons and the like. Instead, we all bought into the notion that exercise, beyond providing a great and rewarding lifestyle, was actually good for us.
New research confirms this common sense outlook. The New England Journal of Medicine reported on a study in its March 14, 2002 issue that the number one determining factor of longevity is the amount of exercise a person gets. Exercise is a greater determining factor of longevity than smoking, diabetes, hypertension and heart disease. The study found that the more vigorous the exercise, the longer a person's life expectancy will be. (You can read more about the study in this Washington Post article).
This research simply confirms earlier research which came to the same conclusion. For example, there was a long term study reported in 1993 of Norwegian men which similarly concluded that the amount of exercise was a long-term predictor of death rates from heart disease and any other cause. The more exercise a person gets, on average the longer life span that person will have. (see various research summarized here.)
What is unreported is the obvious conflict between these empirical studies of actual human beings over decades, which conclusively show that exercise (and the more the better) is good for one's health, and the laboratory research of free radicals which suggests just the opposite. So it is confusing to a layperson such as myself why some doctors, including one of the original proponents of aerobic exercise, Dr. Kenneth Cooper, are so cautious when it comes to training for vigorous events such as triathlons. In my review of this topic, I could not find any empirical studies of endurance athletes suffering higher rates of disease than more moderate exercisers. The only studies available indicate just the oppositemore vigorous exercise provides even more health benefits than moderate exercise (and moderate exercise provides huge benefits over sedentary lifestyles).
While free radicals obviously exist, it would appear that the human body has adapted and easily neutralizes them through naturally created antioxidants. From my review of the articles on this, the worst effect of oxidation from exercise is the temporary sore muscles that result from increases in training. This is one of the many reasons that everyone who gives advice on this site (and other similar publications) urges gradual build-ups in training.
Research support this adaptive view. A couple of years ago, Italian researchers led by Dr. Stefano Taddei measured free radicals in the blood stream and found that athletes, young and old, have much lower blood levels of free radicals than sedentary groups.
It is common to see advice that athletes should take antioxidant vitamins, such as E and C, to counteract the effects of oxidation. It is not clear that this will provide any benefit with regard to reducing possible damage from free radicals (though there are other good reasons to take vitamin supplements). It may be that the body has figured this one out long before the nutritionists got hold of it. Of course, a diet with plenty of fresh fruits and vegetables provides myriad health benefits and will also provide antioxidants to the extent they are needed.
I would invite people to share their knowledge on this subject, especially those who are more informed in health matters. But until I see long-term studies suggesting otherwise, I intend to keep running as far as my legs will take me.
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