The consumption of high quantities of anti-oxidant nutrients (vitamin C, vitamin E, and beta-carotene) has been linked with a reduced risk of cancer, but now there's evidence that the anti-oxidants can help control another troubling problem for endurance athletes - the common cold.

In research carried out by researchers from the University of Witwaterserand and the University of Cape Town in South Africa, 43 entrants in the 90-kilometre Comrades Marathon ingested 500 mg of vitamin C daily for 21 days prior to the 1993 race. Another 45 participants took 500 mg vitamin C plus 400 IU of vitamin E daily, while 37 runners supplemented their diets with 300 mg of vitamin C, 300 IU of vitamin E, and 18 mg of beta carotene (a chemical which the human body readily converts to vitamin A). 47 other runners took in only a placebo, and all runners were matched with sedentary control individuals who took in similar amounts of anti-oxidants or placebo. All subjects were monitored for infections for 14 days after the marathon.

Compared to sedentary controls, runners did have more respiratory system infections during the two weeks after Comrades (very strenuous exercise - like completing a 54-mile marathon - tends to suppress the immune system). However, within the running group, taking in vitamin C or a mixture of C, E, and beta carotene seemed to help prevent infection. Only 16-20 per cent of the runners receiving vitamin C alone or the combination of C, E, and beta carotene became ill, compared with 40 per cent of the runners who consumed a placebo.

It appears that the intake of supplemental anti-oxidants may lower endurance athletes' risks of respiratory tract infections during periods of extreme physical exertion. It's possible that the anti-oxidants may help to stabilize cell membranes in the athletes' respiratory systems, thereby making the cells less vulnerable to viral attack. Vitamin C may be especially protective; the South African researchers found that the group with the lowest incidence of infection consumed about 1007 mg of vitamin C per day.

'Anti-Oxidant Nutrient Supplementation and Symptoms of Upper Respiratory Tract Infections in Endurance Athletes,' Medicine and Science in Sports and Exercise, vol. 26(5), p. S218, 1994
Can exercise lower your risk of lung cancer?

Increased levels of physical activity decrease the risk of colon (but not rectal) cancer, but epidemiologists haven't been sure about whether exercise can limit the incidence of cancer in other parts of the body. However, new information obtained by researchers at Harvard University in the United States suggests that regular activity may reduce the frequency of lung cancer.

At Harvard, investigators Ralph Paffenbarger and l-M. Lee studied 17,755 men (average age = 47 years) over a 28-year period between 1962 and 1990. Activity levels in the men were assessed using mailed questionnaires, and the subjects were classified as either inactive (expending fewer than 1000 calories per week during exercise), moderately active (burning between 1000-2500 calories per week), or highly active (using more than 2500 weekly calories during exercise - the equivalent of running or walking more than 20-25 miles each week). Factors which tend to increase the risk of lung cancer - smoking, age, and body mass - were controlled statistically.

A total of 354 lung cancers occurred during the study, and analysis of the data revealed that physical activity was linked with an appreciably lower risk of lung cancer, especially in men who were highly active throughout the 28-year study. The latter group's incidence of lung cancer was only half as great, compared to inactive males.

Since dietary records weren't kept, it is possible that the more active individuals might have also consumed higher amounts of anti-oxidant nutrients during the study. Since anti-oxidants may be associated with lower frequencies of lung cancer, such dietary supplementation - rather than physical activity - might have been the true source of protection from cancer However, the time period of the research (between 1962 and 1990) was actually before anti-oxidant supplementation became a wide-spread practice, so the anti-oxidant explanation has doubfful validity.

How can exercise protect the lungs from cancerous growths? The actual mechanism is unknown, but it is clear that regular physical activity - as long as it's not carried to an extreme (see the preceding article on ultra-marathon training and the increased risk of respiratory illness) - tends to stimulate the immune system. A fully functioning immune system does a better job of attacking small clusters of cancer cells before they have a chance to develop into full-blown tumours.

The connection between exercise and a reduced risk of lung cancer is a happy one, since lung cancer is the most common fatal cancer in men in both the United States and Europe, accounting for about 20-25 percent of all cancer deaths. In the United States alone, almost 100,000 men die from lung cancer each year.

UA Prospective Study of Physical Activity and Lung Cancer in Men,' Medicine and Science in Sports and Exercise, vol. 26(5), p. S216, 1994