No. It was a correlational study. You can't exactly randomly assign people to go live in certain places for the majority of their lives, so you won't be able to establish a direct cause-effect relationship.
My advisor suggested it could be due to sleep deprivation. That explanation makes some sense. Sleep deprivation has been linked to all sorts of negative health outcomes. It also makes sense that if it's light later at night people will go to bed later, so they get less sleep.
Tom
