According to this article in the Daily Telegraph almost 10% of the British population meet the criteria for depression nowadays, and the average age for the onset of depression is 14 years old as compared to 45 in the 1960s. Setting aside the fact that we know much more about this problem than in the past, when it would not have been so recognised, one has to ask what is it about the modern world that causes this?
I am sure the professionals can come up with all sorts of reasons ranging from increased academic pressure on the young to consumerism to technology and so on and so forth. Probably people also have more time to be depressed now, and they expect more from life than our ancestors did. They see celebrities strutting across the stage of life and wonder why they can't be like them. This is particularly the case for teenage girls, I find. All these things are undoubtedly true and yet there is something more important that goes beyond them, and that is very simply the loss of God.
Depression relates to the absence of meaning. Yes, I know there may be physical problems that can also cause it but fundamentally it is the lack of meaning and purpose in an individual's life that results in a depressed attitude. Meaning and purpose can temporarily be found in many things but ultimately they reside only in the spiritual. When you deny the spiritual it is as though you have cut off the supply of blood to the heart. Eventually it ceases to function. Modern society has denied the spiritual and so it has denied meaning to life. There are no two ways about this. We can and do invent false meaning, through money, sex, fame, drugs, material success, political engagement and the like, but these don't take us very far and the artificial meaning they provide cannot be sustained for long. No wonder depression is on the rise.
Depression is also caused by fixation on the self. This is not a popular diagnosis but it is true. That is why old-fashioned remedies such as taking a walk or doing something for someone else make a lot of sense. But these are perhaps only short term solutions. There is really only one cure for depression and that is to turn to God. Depression is being trapped inside yourself. Only God can really take you beyond yourself.