I run 4 nights a week (3 - 5 miles a night) and do very long runs on Sunday mornings (~ 10 miles) and I must say that I am the happiest, most chipper, and most optimistic person you will ever encounter!
I wake up with a smile on my face, never frown during the day, and fall asleep with a smile on my face. I am incredily happy to be living and look forward to each and every day!
And I attribute it all to exercising. Before I started running, I was still a very optimistic person and incredily content in life... but I found myself to be down and depressed quite often.
I am still young, just started nursing school and I am sooooo excited to get a running start in life. I have probably 60 or 70 years ahead of me and can't wait to see what life throws my way!