4. Avoid heavy exertion
Have you ever heard of the open window phenomenon? During excessive physical exertion - such as when running a marathon - the number of immune cells in the blood increases sharply. If the body relaxes afterwards, the number of immune cells falls below the initial value before exercise. Since pathogens can only be combated to a lesser extent at this time, infectious diseases occur more frequently. So if you do not want to get sick, you should not exaggerate with the effort during sport.