The prevailing wisdom on depression is that lack of sunlight can lead to seasonal affective disorder (SAD), epecially in colder climes such as in Scotland, Scandinavia and so on.
But people living up in the arctic circle, where in summer, the sun literally never sets run into the opposite problem: over-exposure to sunlight for weeks on end. In Greenland at least, this apparently leads to an increase in suicides.
Don’t mess with your body clocks, people.