So many of us are used to worrying about “over exercising,” which may lead to being bedridden by a flu or cold. In fact, this myth has persisted for nearly 40 years, according to researchers of a new study. They busted that old misconception that competing in endurance activities (including competition) will suppress one’s immunity, making them more susceptible to developing a pernicious bug like a flu episode.
The 1980s-era research queried major marathon competitors if they had symptoms of infections following the race and many confirmed that they did, which then mushroomed into the current belief that participation in endurance sports in particular increases infection risk by suppressing the immune system.
New research published in the journal Frontiers in Immunology, unveils new information that seems to refute that old belief.
In a new meta-analysis of research published in the past 40 years, the scientists from the University of Bath (UK) explain that, for competitors taking part in endurance sports, exercise causes immune cells to change in two ways. Initially, during exercise, the number of some immune cells in the bloodstream can increase dramatically by up to 10 times, especially natural killer cells, which deal with infections. After exercise, some cells in the bloodstream decrease substantially—sometimes falling to levels lower than before exercise started, and this can last for several hours.
Previously, the reduction in immune cells after exercise was thought to signify immune-suppression. However, according to the study team, there appears to be compelling evidence that these cells are not lost or destroyed but are deployed to other sites int the body that are susceptible to infection.
They have found that most evidence shows that cells return to normal levels within several hours, which is far too quick for them be replaced with new cells. Second, studies in humans have shown that these cells are able to leave the bloodstream and travel to other body sites.
Third, studies with laboratory animals have shown by labelling immune cells, that following exercise, these labelled cells accumulate in the lungs, and other places, because they go there to look for infections.
The authors therefore suggest that low numbers of immune cells in the bloodstream in the hours after exercise, far from being a sign of immune-suppression, are in fact a signal that these cells, primed by exercise, are working in other parts of the body.
Co-author Dr. John Campbell observed, “It is increasingly clear that changes happening to your immune system after a strenuous bout of exercise do not leave your body immune-suppressed. In fact, evidence now suggests that your immune system is boosted after exercise—for example we know that exercise can improve your immune response to a flu jab [bout].”
Co-author, Dr. James Turner added, “Given the important role exercise has for reducing the risk of cardiovascular disease, cancer and type II diabetes, the findings from our analysis emphasize that people should not be put off 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.”
Campbell, Turner, “Debunking the Myth of Exercise-Induced Immune Suppression: Redefining the Impact of Exercise on Immunological Health Across the Lifespan.” Frontiers in Immunology, 2018; 9 DOI: 10.3389/fimmu.2018.00648
