Well, because you don't have to run to be healthy, there isn't an answer to your question. All forms of movement are good and it's movement that provides the benefit, not one particular form of it. Moving fast, as with running, does give benefits moving more slowly, as with walking, don't, such as moving toxins and nutrients through your body and out -- the more you sweat, the more you excrete, etc. It builds heart endurance by working the heart harder than less cardio based exercise. Etc. But you can do that with an elliptical machine or swimming or bicycling or playing a fast-moving sport. You can do that climbing mountains. You can do that rowing. So running itself isn't a necessary endeavor unless, of course, someone or something dangerous is chasing you! So you run because you enjoy it, knowing it's also one of the most high impact activities outside of contact sports you can do and so also often leads to injuries and long-term problems that lesser impact activities don't, but if running is what you love, then do it. How far you run and how often is up to you and how much you like it. Because, again, you don't have to do it. So run as much as makes you happy. But it's wise to alternate activities at least some, and getting some resistance training in as well and flexibility training can at least potentially reduce the costs of running. Peace.