It's interesting that there are now three global studies that show that virtually every type of exercise extends life span except one. Marathon running. The extended steady state cardio tends to kill you off earlier. Short intense bursts are much better for your heart. Remember, Jim Fixx who started the running craze in the 70's with his book "The Joy of Running" - kicked off in his 40's while running. That's why I limit my runs to 5K and when I'm ripping up I rely on interval and circuit training.
I am more concerned about the physical damage that is done by the constant pounding to the body (other than a heart attack like Fixx). Although, apparently the pounding can affect the heart, too.
Anyway, add 20 to 50 pounds to the body and it compounds the problem. Not that a person who is overweight would be running a marathon. However, they may attempt it and train. Best to lose the weight first.
True there are shoes that reduce the impact force. It helps, but there is still a huge amount of force being applied to the legs, back, and body and continuously for a long period of time. Not good.
One thing that will end an exercise regimen the quickest is an injury. I wish that I had been more careful in my younger days. I have knee issues, too. I remember having shin splints so bad that I couldn't walk up stairs. This is why I chose a bike and hiking. Although I tended to load up my backpack for the day hikes — I believed in “being prepared.”