I'm struggling to find it but I definitely remember reading a paper that claimed that aerobic exercise in over 60s decreased heart attack risk (which is good, obviously) but increased stroke risk.

I think the biggest risk though is acutely doing high intensity exercise (e.g. a marathon) whereas doing low intensity regular exercise (e.g. a 5k jogged at moderate pace 4x a week) is probably good.

So it's not "running is bad", it's more "running insane distances and/or running at insanely high intensity is bad", but the issue is a lot of people who get really into running end up doing one or both of those things.

One sign that marathons (let alone ultramarathons) may not be particularly healthy is that the first guy to do one famously died, and then subsequently people die doing them every single year. Yes the risk is low overall, but that doesn't mean it's actually good for you

> One sign that marathons (let alone ultramarathons) may not be particularly healthy is that the first guy to do one famously died, and then subsequently people die doing them every single year

I don't find this line of thinking terribly convincing

It's well known that (even young) elite athletes with unknown inborn heart defects sometimes die after extreme exertion. But it doesn't really follow that "extreme exertion is bad for you," the lurking variable is the heart defect.