Finland leads the world in per capita coffee consumption. My pet theory is that in the winter it fights depression, and in the summer the sun is out late at night and you're saying to your friends: How could we possibly go to sleep now?! Moar coffee!!

I tend to find coffee increases jitteriness and anxiety in people. Some evidence it may increase depression too.

Well, maybe not so much fight depression as fight lethargy ?

In my experience, even that is not true. It displaces it.