Athletes who complete a marathon distance run may be almost 20% more likely to get a post-run respiratory infection, a meta-analysis of research has found.

Published in Exercise Immunology Review, researchers from the University of Birmingham have analysed data from 17 years of studies on marathon runners developing upper respiratory tract infections (URTIs).

The team included papers published since 1990 comparing the same runners before and after a marathon. Runners faced an increased risk of developing infections post-marathon, and using statistical weighting, the risk of getting a URTI averaged out across all papers is 18%.

Dr Amanda Sardeli, Research Fellow at the Institute of Inflammation and Ageing at the University of Birmingham, and lead author of the paper, said: “This is the first consensus to confirm that this special type of competition that combines high intensity with a very large volume of exercise leads to a higher risk of upper respiratory infection. Contrary to expectations, younger individuals have a higher chance of getting an infection than older runners, which might be due to their experience with training progression and the discipline to follow a strict schedule and diet, for example.

“It is still debatable if the exposure to crowds in this type of competition is the real problem, since in other studies, the same higher risk of infection in athletes during crowded competitions can be seen in non-athlete staff members. In fact, the stronger candidate to explain this phenomenon is the energy depletion that occurs during the marathon and is well known to affect immune functions.

“Furthermore, the present study combined the results of old races, and specialists believe that, nowadays, athletes have more information about the importance of carbohydrate supplementation and usually replace their energetic needs before, during, and after the race, reducing the impact on the immune system.

“Exercise is clearly an important aspect of a healthy lifestyle, and other research points to its beneficial effect on immune regulation. This study does highlight that strenuous exercise can have a detrimental impact on our bodies, and athletes need to take care and be aware of the impact that a marathon is likely to have on their immune system.”