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I like to run. At the end of September I run my 6th marathon and fell ill the week after. Again. This has happened to me nearly every time post marathon. Isn’t running supposed to improve our health? Time to find out what happens to our immune system when we exercise.
Moderate levels of exercise are actually associated with a lower risk of infections. A study in 2007 showed that recreational athletes had a lower risk of developing upper respiratory infections (e.g. the common cold) than sedentary controls. Elite athletes analysed in the same study also had a higher risk of falling ill compared to the moderately active group, indicating that there is a sweet spot for how active one should be to have a highly functional immune system.
Experts refer to the 3-72 hours post marathon (or any type of extreme fitness event) as an open window for infections. The “open window” theory as been coined by Dr. David C. Nieman, a professor in the Department of Health, Leisure, and Exercise Science at Appalachian State University. In a study, initiating the field of exercise immunology, he surveyed participants of the Los Angeles Marathon and found that 12.2% of participating runners fall ill in the week following the marathon, while only 2.2% of similarly trained runners, who did not participate in the marathon, reported an infection.
What happens to our body during exercise?
Our bodies respond to exercise by releasing immune mediators such as IL-6. These molecules initially activate immune cells, making them more alert to possible pathogens. Monocytes and macrophages for example, expand in numbers during active exercise. This and the increased blood flow to the mucus of the nose and lung can help defend us against pathogens during moderate exercise.
Muscle cells produce IL-6 locally. This may, at least in part, be the muscles way to recruit immune cells to help with possible damage following exercise. IL-6 is subsequently responsible for the release of other cytokines such as IL-10 and cortisol, a key stress molecule. Both the immune mediators and cortisol induce an anti-inflammatory response, which can help get rid of low-grade chronic inflammation and therefore explain how exercise can prevent inflammation-driven diseases such as diabetes and heart disease.
The amount of mediators released correlates with the length of the sporting activity. Long lasting exercise can send the anti-inflammatory response into overdrive, limiting the immune systems ability to react to infections. The effect is spread across different immune cells types – including decreased NK cell toxicity, decreased lymphocyte proliferation and antibody (IgA) productions. This review from 2000 nicely summarised known effects.
These effects sounds dramatic, but in fact it is not only limited in time – our immune system recovers within 1-3 days – it also does not mean marathon runners are immune deficient. Marathon runners are still able to fend of pathogens. But they are – statistically – more prone to fall ill because of the effect of running.
Tips to stay healthy
The impairment of the immune system will not make us ill. Exposure to pathogens will. It is therefore key to avoid exposure post marathon. Sure this is easy to say, when you run in a group of 40 000 people, with 1 million people on the sidelines cheering. Still wash your hands after the race and try to avoid too much close contact with people right after you finish.
Stay hydrated. Dehydration causes your throat to be come dry, leaving it more vulnerable to pathogens.
Eat/Drink carbohydrates. Immune cells cannot function without the glucose that fuels them. So make sure you take up carbohydrates right after the race to help the recovery of your immune cells! In addition try to also fill up on green vegetables, beans and fruits which are rich in vitamins, zinc and iron – all of which can boost your immune system.
Sleep. Sleep deprivation is stress, and as we learned above stress hormones such as cortisol can hinder your immune cells. No feeling bad about that snooze button for at least a week after the race!