Endurance Sports Don't Weaken Immune System

By Jane Farrell

New research overturns a myth that competing in endurance sports such as marathons suppresses the body’s immune system and makes competitors more susceptible to infections.

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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. Many did, leading to a widespread belief that endurance sports increase infection risk by suppressing our immune system.

Now a new article, from researchers in the Department for Health at the University of Bath, in the UK, reinterprets scientific findings from the last few decades and emphasizes that exercise – instead of dampening immunity – may instead be beneficial for immune health.

The study was published in the journal Frontiers in Immunology.

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 study, the authors from the university 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, according to a news release from the university, 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.

As a result, the authors suggested 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.

The authors suggest that although a strenuous exercise bout itself will not increase the likelihood of catching an infection, other factors might. Attending any event where there is a large gathering of people, increases your chance of infection. Second, public transport, particularly airline travel over long distances, where sleep is disrupted, may also increase your infection risk. Other factors, like eating an inadequate diet, getting cold and wet, and psychological stress, have all been linked to a greater chance of developing infections.