Running marathons and competing in endurance sports boosts the body's ability to fight off illness, new research suggests.
The findings debunk the myth that has persisted for nearly four decades - that strenuous exercise, such as the London Marathon, suppresses the immune system and makes competitors more susceptible to infections.
Research from the 1980s, which focused on events such as the Los Angeles Marathon, asked competitors if they had symptoms of infections in the days and weeks after their race.
In advance of this weekend's #LondonMarathon2018 read about our latest @Health_at_Bath@Cancer_at_Bath research from @JamesE_Turner & @JCampbell_PhD which debunks the long-standing 'myth' that strenuous #exercise suppresses the immune system https://t.co/qQCaJk0k8Xpic.twitter.com/wNCLmGYkRq
-- University of Bath (@UniofBath) April 20, 2018
Many did, leading to a widespread belief that endurance sports increase infection risk by suppressing our immune system.
Scientists at the University of Bath have reinterpreted scientific findings from the last few decades and emphasised that exercise - instead of dampening immunity - may instead be beneficial for immune health.
In a detailed analysis of research articles that have been published since the 1980s, this new review of the literature has reinterpreted findings, based on fundamental principles of immunology and exercise physiology, to clarify misconceptions and misinterpretations that have formed over the years.
In their reinterpretation, the authors 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.
Many scientists previously interpreted this fall in immune cells after exercise to be immune-suppression.
However, strong evidence suggests that this does not mean that cells have been "lost" or "destroyed", but rather that they move to other sites in the body that are more likely to become infected, such as the lungs.
Dr John Campbell said: "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."
Co-author Dr James Turner added: "Given the important role exercise has for reducing the risk of cardiovascular disease, cancer and Type 2 diabetes, the findings from our analysis emphasise 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."
The authors suggest that although a strenuous exercise bout itself will not increase the likelihood of catching an infection, other factors might, such as attending an event where there is a large gathering of people, airline
travel and poor diet.
- The study, Debunking the Myth of Exercise-Induced Immune Suppression: Redefining the Impact of Exercise on Immunological Health Across the Lifespan, is published in the journal Frontiers in Immunology.