Exercise is usually very effective for depression, but there are a lot of people who can’t do it in any meaningful way, due to other medical conditions/injuries. In a lot of cases, the inability to exercise as one used to is at the root of the depression.
Yes, and in that case you may try to get them into chewing gum:
Relieved Anxiety: When chewing gum, participants reported lower levels of anxiety.
Gum chewers showed a reduction in anxiety as compared to non-gum chewers by nearly 17 percent during mild stress and nearly 10 percent in moderate stress.
Increased Alertness: Participants experienced greater levels of alertness when they chewed gum.
Gum chewers showed improvement in alertness over non-gum chewers by nearly 19 percent during mild stress and 8 percent in moderate stress.
Reduced Stress: Stress levels were lower in participants who chewed gum.
Levels of salivary cortisol (a physiological stress marker) in gum chewers were lower than those of non-gum chewers by 16 percent during mild stress and nearly 12 percent in moderate stress.
Improved Performance: Chewing gum resulted in a significant improvement in overall performance on multi-tasking activities. Both gum-chewers and non-chewers showed improvement from their baseline scores; however, chewing gum improved mean performance scores over non-gum chewers by 67 percent during moderate stress and 109 percent in mild stress.
http://www.eurekalert.org/pub_releases/2008-08/epr-nrf082908.php
High levels of cortisol for a long time is probably a very common cause of depression. However, the etiology is very complex.