Before, when we talked about the heart ramifications of endurance training, "scientists" and "doctors" were telling us that 20 miles per week was the maximum anyone should do to avoid irreversible damage to our hearts. Certainly, other "doctors" and "scientists" disagreed. And with the recent loss of one of our own, we need to take these things seriously.
Now, another group of "scientists" and "doctors" has come up with a number slightly higher and more palatable to the running masses (or is it asses? hee hee hee). But they do show increased atherosclerosis in cardiac vessels with increases in the amount of endurance training past a certain point. Here, they say 35 miles/week. That is MORE hardening of the arteries in runners than in couch potatoes, other factors being equal.
I find these theories quite reasonable, even if trying to quantify the exact number is probably fraught with chaotic uncertainty. Just as "scientists" with a gun to their head can't tell you the temperature within 2.0 degrees for certain 3 days from now, others will attempt to tell you the temperature with conviction 85 years from now within 0.01 degrees.
I say use butter to fry your eggs and have an extra helping of bacon. Then go out for a ten-miler later today.