Having done some child develpment and psychology studies these things are fairly well researched to the point of being general knowledge me thinks.

People in countries that don't get much sun suffer from depression that is treated with sitting them in front of bright lights.

Depression patients in one study who were exercised did equally as well as patients put on anti-depresent meds.

Water, diet, fresh air, sunshine we all need these things to stay healthy any doctor would tell you the same.

Blessings
Cat.