alt Hacker NewsRisk of stroke is the most obvious (and fairly concerning) one where there's solid data.
Also there's "distance running" as in running maybe 50k a week, that's probably okay, although as you get older it will increase your risk of stroke. But ultramarathons are a whole different ball game and almost certainly bad for you
Can you link the data? I don't buy it.
https://pmc.ncbi.nlm.nih.gov/articles/PMC11720530/ says there's a higher rate of AF in older, male althetes but a lower risk of stroke compared to similar aged, non-athletes.
At any rate, the data doesn't seem clear enough to claim that "distance running bad for you" or "any distance over 50K is bad for you".