Creative vs. Depressive

It is a quetion brought to my attention by Michael Rosen in his picture book "Michael Rosen's Sad Book", where he asks the question - "Why am I always sad?" My immediate responce, whether it be because I was thinking of art at the time or otherwise was, "Because you're a
creative." Little did I know that this was directly linked to my own life. It suddenly offered explanation to my sometimes depressive state of mind.
Is there any link between being a creative and being depressed. Many artists have been in such states. We know Colin McCahon had serious depression concerns in the later stages of his life. Michael Smither's admitted to having depression set in on his life in a documentary on TVNZ. Jackson Pollock was well publiscized for his drunkeness, most probably brought on to counter depression. So what is it about creatives that brings about depression. What is the nature of depression? There are two ways in which the two can interact.

1. That the ability for an artist to create is or can be heavily
   influenced by the emotion and feelings of depressions.
2. That the result of the act of creating is the onset of
   depression.

Both of these are viable options. There have been times where I have created in a depressed mood, and it heavily affects the resulting output. On the other hand, it is also entirely possible where the act of creating - an emotional rollercoaster full of stress, concentration and personal out-pouring leads to a state of depression.
There is no evidence however to suggest that depression is an inevidable bi-product of creativity. There are plenty of artists who do not get any signs of depression because of their creative nature. There is however weight to the arguement purely because so many great
artists have struggled with depression, whether it be a fuel for their creative passion or a mere bi-product of their artistic genius.