What does the proverb a cheerful heart is good medicine but a broken spirit dries up the bones mean?

It means that if in your heart you are cheerful and happy it is good for your body but if you get a broken spirit your body will soon follow. Just look at what depression does to people. Depressed people look like the living dead, no offense to Zombies, the don't want to do anything and they act as if the world has ended but they alone survived to cast into a never ending void of darkness.