I believe if one is conscious of some basic laws of nature, then running can increase the immune system to ward off illness.
With proper rest and a decent diet combined with respecting the law of nature, I have not been ill to the point of being bed ridden for over 20 years now. My formula is the following:
When feeling a cold or flu coming on, slow down your running and activity but don’t stop your daily cycle, just slow down. Take it at a slower pace. Most medical doctors agree that resigning oneself to the bed may be the worst thing one can do and there are many reasons, including physiological and mental effects.
Then there are antibiotics. I have not taken one in over twenty years. I am not a medical doctor and if I have a real illness which I understood antibiotics were needed, then for sure I would follow my doctor’s advice. But I believe they can break down one’s immune system over time.
So what to do when you feel a cold or flu coming on? Drink plenty of water. During your run, try to spit out as much phlegm as you can. Shorten your runs. Be a little more conscious about diet and use your instincts about your work and daily activities. And relax when you can as you need to slow down. As many doctors say, the common cold is a necessity because it is the warning signs that your system is breaking down. So accept the warning signs and follow some rules of nature and you will find that your immune system will strengthen and will be able to combat major illness and you can avoid a full blown cold or flu.
So we all have different methods. What is yours?