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094: How Running Affects Our Immune System

Jun 27, 2019


For years, we have been taught the lesson that if we workout either long or hard, our body will be so tired and so busy repairing itself, that our immune system will be compromised.  We have possibly experienced a cold following a big race, or have heard anecdotes of friends who fell victim to the dreaded post-race illness.  

On this episode, we look into the research and discuss the current scientific understanding of exercise and our immune system. 

First, let’s start with this:  the immune system is incredibly complex.  There are dozens of cells used together inside the body to fight off infections and diseases in a complicated dance that we are just not getting into.  Many of the studies checked for levels of specific markers, or one of the immune system cells, in the bloodstream. When results showed a drop in cell count, it was concluded that the immune system was weakened.  End of story.  

Second, many of the studies were large surveys where the subjects answered whether they were showing symptoms of being sick following a race.  Now, I don’t know about you, but following a marathon or half marathon or local 5k, I have a cough for a few hours and feel fatigued for a few days to a week or more.  However, if I actually went to a doctor, I would not have any clinical diagnosis, because I am not sick.  

Third, there are pretty good studies to show that moderate activity performed on a regular basis will lead to lower incidence of illness than a sedentary lifestyle.  There is also some research that has shown that following long or difficult exercise sessions, there is increased incidence of illness. This has lead scientists, who love an easy to interpret graph, that there is a J-shaped curve comparing level of exercise to risk of respiratory illness.  Nothing is bad, too much is bad, there is a sweet spot of moderate activity in the middle.  

Fourth, in studies on older populations, those who were the most fit and active also showed significantly reduced amounts and intensities of sickness during a year.  So even if the J-curve is correct, the very long term results show a substantially boosted immune system after years and years and exercise.  

Fifth, newer research suggests that the immune cells that were lowered in the bloodstream following exercise are not actually gone.  In fact, they seem to migrate to the lungs, essentially setting up armor in defense of possible diseases they may be faced with.  

Finally, there are a slew of mitigating circumstances that may be causing sickness in the athletes used in the studies.  One of the biggest causes of a weakened immune system is lack of sleep and disruption to a normal sleep pattern. Traveling to destination races is very likely to cause this.  Also, travel itself is linked to increased likelihood of illness. Surrounding yourself with lots of other people will also increase your chance of getting sick. Lastly, the increase in stress around a big race releases all sorts of hormones that suppress the immune system. 

Ultimately, the science supports the idea that exercising is better than not exercising.  There is inconclusive results and more research needed on high levels of exercise. The research needed can cover ways to combat a lowered immune system from sleep to food, where the “high level” actually begins, and how high level changes as an individual’s fitness improves.  




Hope you enjoy it!! Let us know if you have any questions that you would like answered on our show!    

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