The Daily Beast has an important article on depression in competitive female distance runners. I have seen the affects that depression can have on people first-hand and it is very sad.
With that said, I do not believe that running is itself to blame for depression and suicides. In fact, running is one of the best ways to build confidence and feel better about yourself.
However, I do think that competitive running sometimes appeals to a certain kind of person: perfectionist, driven, type A, that may be more prone to experiencing feelings that they are never good enough, which can lead to a depressed mental state.
I think the lesson is that fellow runners and coaches need to understand the symptoms of depression and work to get affected runners the help they need.