Running is good for you because it helps you keep your figure and health in tip-top condition, but some people run too much and too far in a single sitting, and experts rule in on why this is bad for your body and your health.
Among the various kinds of things too much running can do are:
• Cause your internal body temperature to rise to feverish conditions
• Cause major dehydration from fluids lost by sweat
• Cause risk for hypothermia from extreme loss of body heat too quickly
• Cause kidney issues
• Cause your body to starve from too many burned calories compared to intake
There may also be other things that can be problematic from over-running, but these are some of the most notable.
For what it's worth, these problems are more likely to affect those who run long marathons, and not particularly those running only short distances. Marathons can be several miles long, with most averaging 26.2 miles.
With that in mind, running is still good for your cardio, so don't be afraid to do it in moderation.