Numerous studies have shown that moderate exercise boosts the body’s immune system. In this video Professor David Nieman of Appalachian State University explains that, incontrast to moderate exercise, extreme exercise can actually depress your immune system.
Bottom line:
• Regular moderate exercise reduces the chances of your getting ill
• Extreme exercise can multiply the chances of your succumbing to an infectious disease as much as sixfold.
The trouble with these sorts of epidemiological studies is that we are dealing with two distinct groups of people, those who engage in extreme exercise and those who exercise moderately. Perhaps there is something in the makeup of people who go in for extreme sports that makes them more susceptible to infection. Perhaps even if they were to change their exercise pattern they would still be more vulnerable to infection than people whose natural inclination is to exercise moderately.
Professor Jeffrey Woods works with mice rather than humans. Working with mice has the advantage that it is possible for him to decide which mice exercise and how hard they exercise. The mice have no say in the matter.
In 2004 Professor Woods found that sedentary mice are most vulnerable to the affects of infection but mice that exercised moderately did better on average than mice that were forced to engage in extreme exercise. Since Professor Woods’ mice had no say in their exercise regime it cannot be the something in the makeup of the mouse that caused the extreme exercise group to become vulnerable to infection. It could only be the extreme exercise itself.
Now Professor Woods has gone a step further. In a recent paper in Exercise and Sports Science Reviews titled Exercise and Respiratory Tract Viral Infections Professor Woods and his team identify the mechanism that cause extreme exercisers to become more susceptible to respiratory tract infection. And thereby hangs a fascinating tale.
When a bacterium, virus or some other pathogen enters your body your immune system mounts a furious all-out assault on the “invasion site”. We experience this as inflammation. The animation below shows what happens.
So far so cool. But at some point the initial inflammatory response needs to be turned off. If it persists it can cause problems. It is now believed that a number of diseases including arthritis, cardiovascular disease and cancer can result from persistent inflammation.
The inflammatory response is mediated by T-helper cells. It turns out that there are two distinct types of T helper cells called Th1 and Th2. The Th1 cells start the inflammation going and the Th2 cells damp it down.
Th1 cells are the “on” switch
Th2 cells are the “off” switch
It turns out that moderate exercise suppresses the Th1 response a little and bolsters the Th2 response. This results in a gentler immune response than sedentary animals experience.
But extreme exercise suppresses the Th1 response too much. The inflammation dies down before it has destroyed the invading virus.
Tags: appalachian state university, david nieman, jeffrey woods, th1, th2, university illinois
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