I agree, it's for other than health that one does this.  After 35 years of marathon training I found I had heart and other health issues, turns out most of the guys I know who did the same have similar issues (though I do notice they tend to be Type As, I'm more B).  Google confirms the perils of decades-long endurance training.  You can likely get away with it for a while if you quit soon enough.  After 3 years of slow jogging 20 minutes 3 times a week my white blood cell and other readings are starting to come back near normal - not sure about the heart as I'm not going back to the heart docs any more, just crossing my fingers on that one.