I have a running friend who is an inspiration to many including me. First he is a psychiatrist and second he is an iron man competitor. He said that 20 years ago he noticed his peers in very poor shape (he is 70 now) so he decided to get into running. That turned into biking and then tri athalon and eventually the full length iron man. He will be competing in Kona HI this october hoping to win his age group.
He says the first thing he does when he has someone come in to his office with depression is to place them on an excercise program. It is something that is hard to judge when you are doing it, but I always feel good while I am running and there is a reason. Our brains are just a bunch of grey mush but it is very delicate grey mush. The brain likes it's chemicals just so. We don't give it the right chemicals by sitting at a desk all day. Start the day with a good workout and see what it does for your disposition. Works for me.