Depression and the emotions associated with it can be contagious, according to a new study.
Researchers have found that the gloomy mindset of students vulnerable to depression can be catching, making their friends more likely to suffer the condition six months later.
The research follows studies showing that people who respond negatively to stressful life events - interpreting them as the result of factors they can't change and as a reflection of their own shortcomings - are more vulnerable to depression.
This "cognitive vulnerability" is such a strong risk factor for depression that it can be used to predict who is likely to experience depression in the future.
Doctors Gerald Haeffel and Jennifer Hames, of Indiana's University of Notre Dame, said that this vulnerability seemed to establish itself in early adolescence but remain stable throughout adulthood.