What's the reason for melancholic depression?

Melancholy is sadness and depression and generally feeling down. Interestingly enough it comes from a Greek word that means “black bile.”

Cause #1: Gallbladder issues

Bile is a liquid that is being produced by your liver and is stored in your gallbladder. If you have a lack of bile production in your body, whether due to gallbladder or liver issues, this can cause severe melancholy.

The reason is that if you lack bile you will not be able to absorb vitamin D and DHA (a type of omega-3 fat that is needed for a good emotional state, among other things) from your diet. These 2 nutrients, if deficient, can have the side effect of severe depression.