Just getting out for 30-40 every day minutes and sleeping and eating well does wonders for me. I get energized and life becomes full of opportunities, I see the bright side of people...
I am almost certain that is the circulation of the lymphatic system. For people working in front of a computer for hours a day it is very important.
Spain(most of it) is sunny most of the year and it is rare when I could not exercise outside, but in central Europe I notice it a lot with the dark winter.