I'm actually not. This is a legitimate concern I have as it took a lot of convincing for me to really start researching the prolonged effects that distance running has on the human body (i.e. not just knees and joint issues). Note, I used to run quite a bit during my undergraduate college years. And I have a few older friends who were dedicated runners like you and leggo. But now have chronic health issues that have been proven to be linked to their distance running days. Hence my comments above, though not accompanied with much detail I admit.