It's linked to eating disorders, major depression, and low self-esteem.

Experts were able to refine a test so that measuring levels of only three was sufficient to diagnose major depression.

Past studies showed 70 per cent of those with major depression experience anhedonia - a loss of pleasure or motivation.

Men with major depression manifested significantly decreased ability to read nonverbal cues when compared with euthymic men.

These included bipolar, major depression, anxiety, panic, obsessive-compulsive disorder and eating disorders.