How exercising leads to the loss of immune cells and why this is a good thing

By Catherine Orda | Photo by Victor Freitas /Unsplash

The knowledge that exercise has apparent health benefits is not lost on anyone, much less on the people who frequent this site. The association between leading an active lifestyle and being in good health is so deeply imbedded in our collective consciousness such that the two are sometimes taken to be the same thing. Yet the idea that physical activity keeps people from getting sick remains to be controversial, partly because of some general notions we have about the immune system (that it’s something that should be protected from physical strain and bacteria, for instance).

But these notions are not unfounded. Research from the 1980s showed evidence that strenuous activities like running marathons actually heighten the risk of contracting an infection, thus leading to the widespread belief that engaging in endurance sports can make a person more susceptible to sickness. Recently, however, there have been studies that tried to reevaluate this belief, with some suggesting that we’ve been looking at it all wrong: Exercise actually ups the immune system’s performance.

How Exercising Affects the Immune System

Exercise affects the immune system in two ways. The first effect takes place during exercise, where a person’s immune cells in the bloodstream can increase by up to 10 times. A type of immune cell that undergoes this dramatic increase is the “natural killer cells,” which are responsible for combating infections. The second effect happens after exercise, and is characterized by a substantial decrease in immune cells. This fall in immune cells, which can last for several hours, has led many scientists to consider exercise as a cause of immune-suppression or as a dampening of the immune system’s performance.

But a recent study from the University of Bath is suggesting that this is not the right way to interpret this information: A fall in immune cells does not necessarily mean that cells have been lost or destroyed. These “lost cells” have actually just moved to other areas in the body that are more likely to become infected such as the lungs.

How Exercising Boosts the Immune System

The authors of the University of Bath study have found evidence suggesting that “losing” cells after exercising just means that the cells have left the bloodstream in order to work on other parts of the body. Primed by exercise, these “lost immune cells” are able to travel to and protect other sites in your body that would otherwise be neglected had you not engaged in exercise.

“The findings from our analysis emphasize that people should not be put off by exercise for fear that it will dampen their immune system. Clearly, the benefits of exercise, including endurance sports, outweigh any negative effects which people may perceive,” says co-author Dr. James Turner. He also adds that the role exercise and endurance sports play in reducing your long-term disease risk outweighs any fears that it will negatively affect your immunity.

The positive effects of exercise on the immune system are manifested in obvious ways—for one, you’re less likely to contract infections. But a less apparent benefit has to do with vaccines. If you exercise regularly, or more specifically, if you exercise just minutes before receiving vaccination, your immune system will respond to the medicine quicker.