intelligence and depression

so....I had a conversation with a co-worker tonight, in which we observed: Of all the people we knew who had at some point suffered from clinical depression, whether diagnosed or not, it seemed the more intelligent (un-quantifiable opinion based observation) the person, the more apt to or severe the depression was.  So i pose the subject,  Is intelligence a factor in clinical depression? If so, or if not, why do you believe so?