Can too much running kill you?

That seems to be what some recent medical studies and one story in the Wall Street Journal seem to be asking.  In the article "One Running Shoe in the Grave"  http://online.wsj.com/article/SB10001424127887323330604578145462264024472.html?mod=e2fb the following quote from the British journal Heart appears,"Running too fast, too far and for too many years may speed one's progress toward the finish line of life."  The study indicates that while runners have a significantly lower death rate than non runners, as one gets older, running more than 20 to 25 miles a week erases the benefit that runners have. The source article is at http://heart.bmj.com/content/early/2012/11/21/heartjnl-2012-302886.extract.jpg     (I could only read the first page.)    The editorial is entitled "Run for your life...at a comfortable speed and not too far"  The authors, James O'Keefe and Carl Lavie, also state that running vs non running provides great benefits health wise, running at a pace faster than 8 minutes per mile provides no additional benefit. 

Beyond this guidance is a warning.  Studies they cite show damage to the heart occurs from high intensity exercise sessions greater than one to two hours.  These can cause "acute volume overload of the atria and right ventricle, which can bring about overstretching and micro-tearing of the myocardium." These are evidenced by a rise in cardiac bio-markers.  Usually after a week these markers return to baseline.  However "after years and decades of "excessive exercise" and repetitive injury" these can lead to "patchy myocardial fibrosis".  The fibrosis and scarring can potentially create a potential substrate for arrhythmias. 

In a video from Dr. O'Keefe's talk at TED http://www.youtube.com/watch?v=Y6U728AZnV0 he shows slides showing veteran marathoners (those who had run more than 25 marathons) had increased levels of plaque in their arteries.  Dr. O'Keefe then talks of Cardiomyopathy.  He cites the case of Micah True, the ultramarathoner mentioned in the book, Born to Run.  Micah died in March of this year while on a relatively short training run in the mountains of New Mexico.  His autopsy showed a thickened heart with scar tissue.  The coroner indicated cardiomyopathy as the cause of death.  

My question is after how many marathons does fibrosis and scarring occur?   Dr, O'Keefe says one marathon won't hurt. But if I train for and run one marathon a year does that put me at risk? Should I stop running marathons after age 50?  What of  90 year Michael Freemont, who recently set an American age group record for the marathon?  And what about the rat study?  The marathon rats..http://circ.ahajournals.org/content/123/1/13.abstract  After 16 weeks of intense exercise the rats showed cardiac fibrosis and increased arrhythmia inducibility.  However the study also stated the following, "The fibrotic changes caused by 16 weeks of intensive exercise were reversed after an 8-week exercise cessation."  So if I take 8 weeks off after my marathon does that mean I am OK and that my heart is fully recovered?

I have run two marathons over three years time and am currently training to run a third in January.  My training run this morning was one hour and 15 minutes, a bit more than needed to gain full benefit in terms of postponing my mortality.  ;-)  Saturday's run will be closer to two hours.  So maybe I'm still ok according to Dr. O'Keefe.  Just a couple of runs greater than two hours these next few weeks.  I am thinking if I qualify for Boston and if I run that in 2014, I may just run half marathons and less for a few years.  Something to think about.  Maybe by 2014 we will some new research to evaluate.  

Feel free to comment if you have any thoughts or questions.  

Merry Christmas to you and Sic'em Bears!