I've read somewhere that ultra running is bad for your body, and that even marathons take their toll. Does this mean that if I don't care about the glory of finishing marathons and ultramarathons I could just as well never (or seldom) participate in such events?
Some background information… I'm not an elite runner, so my main reasons to run are to stay healthy for as long as possible and to enjoy the physical exercise. In most of my 200 races so far I've pretty much run in the middle of the pack, and only won twice in my life (through lack of competition, though).
I've only run two marathon races in the past 15 years (10 and 5 years ago), both of which I didn't really enjoy. I'm much more comfortable doing races up to the half marathon distance, since, for me, they never last longer than two hours. I occasionally do longer training runs (28km), but find those utterly boring, not fun to do, and my experience is that they are rather stressful on my body.
Additional information: Many blog posts I found on this subject seem to be based on this study by the Mayo Clinic from 2012,
Since I'm not a sports scientist, I cannot judge how valid this study is.
I supposed that since how much distance is too much depends on the person, no blanketed statement can be made above what weekly distance running becomes a health issue.
Furthermore, one can find articles that claim athletes can prepare for ultras with a modest weekly mileage, based on the philosophy of Crossfit Endurance. It seems that the high volume of training distance in preparation is what makes marathons and ultra-marathons such a health risk, though I haven't seen any scientific studies backing up this claim.