Your marathon brain could be making you sick

November 30, 2025

Maybe you’ve experienced it: you cross the finish line of your marathon feeling strong, only to wake up a day later with a sore throat and a headache. It turns out the problem might not be the race itself, but everything swirling in your head beforehand. In a study published in the European Journal of Sport Science, a group of researchers from Liverpool John Moores University and Bangor University set out to understand why so many runners catch a cold after a marathon, and the answer wasn’t just about hard training days and logging big mileage.

The researchers observed a clear pattern. Runners who reported higher stress, anxious thoughts, or unsettled moods before the race were more likely to experience a dip in mucosal immunity, and they were also the ones who tended to contract a cold after the marathon. The researchers conducted a second, smaller study in the lab, this time using an hour-long treadmill run, and observed a similar effect, particularly in men. If your stress levels were already running high, the body’s first line of defense didn’t bounce back as smoothly.

The story was less straightforward in women, likely because hormones, cycle phase and contraceptive use can all influence immune markers. The researchers were clear that more work needs to be done there.

The researchers observed a clear pattern. Runners who reported higher stress, anxious thoughts, or unsettled moods before the race were more likely to experience a dip in mucosal immunity, and they were also the ones who tended to contract a cold after the marathon. The researchers conducted a second, smaller study in the lab, this time using an hour-long treadmill run, and observed a similar effect, particularly in men. If your stress levels were already running high, the body’s first line of defense didn’t bounce back as smoothly.

The story was less straightforward in women, likely because hormones, cycle phase and contraceptive use can all influence immune markers. The researchers were clear that more work needs to be done there. Running Magazine