Question: what makes people sad?

Helen O'Connor answered on 14 Jun 2011:

The brain has a huge number of chemicals or neurotransmitters, and all of our emotions are caused by different mixtures and levels of these – which can be triggered by different situations.

Low serotonin levels have been associated with sadness or depression and the same for low dopamine levels.

But the good news is that normal production of these same chemicals makes us feel happy: Serotonin is made with an amino acid called tryptophan which is another chemical that helps us feel happy and controls our moods, sleep and anxiety.