Researchers from the University of Cambridge have found that adolescents whose saliva levels are elevated, the stress hormone cortisol during depressive symptoms, are many times more likely to develop clinical depression or major depressive disorder.
Clinical depression is different from the bouts of bad mood that everyone visits from time to time. Doctors believe that chronic depression 
occurs in every sixth inhabitant of the planet and has symptoms such as increased fatigue, loss of interest in anything, problems with sleep and appetite, low self-esteem, a gloomy vision of the future, and so on. It is believed that clinical depression will become the main disease on the planet by 2030.
“Depression https://en.wikipedia.org/wiki/Depression_(mood) is a devastating disease that affects 10 million Britons,” says study leader Ian Goodyear. “With our research, we can now identify adolescents who are most likely to develop it in adulthood. This will help us take preventive measures and try to reduce the risk of the disease.”
Scientists measured the level of cortisol in the saliva of nearly 2,000 teenagers aged 12 to 19. Two more examinations were carried out, one year and three years later. It turned out that adolescents with elevated levels of cortisol in saliva in the morning and symptoms of depression were 14 times more likely to develop symptoms of clinical depression than those whose cortisol levels remained normal.
