While not clinically depressed, I did have a rough patch a few years ago due to circumstances which included an injury that precluded riding. Vitamin D and joining an improv comedy troupe helped. As soon as I was able to walk for more than 10 minutes, that helped; as soon as I was able to jog half an hour on the treadmill that helped more, and when I finally made it back to commuting by bike, I was myself again...except I was even better as I continue with the vitamin D and the improv comedy troupe. The improv is not so much about being funny as it is being positive. I believe most of depression is chemically based, but training yourself to build on the positive aspects of unexpected situations you have no control over doesn't hurt.