London, Feb 18 (IANS): Researchers from University of Cambridge have identified the first biomarker - a biological signpost - for major depression.

"Teens who show depressive symptoms and elevated levels of the 'stress hormone' cortisol are up to 14 times more likely to develop major depression than those who show neither trait,” warns research.

This could help identify those boys in particular at greatest risk of developing the illness and provide treatment at an earlier stage.

Major, or clinical, depression is a debilitating mental health problem that would affect one in six people at some point in their lives.

However, until now there have been no biomarkers for major depression.

“We now have a very real way of identifying those teenage boys most likely to develop clinical depression. This would help us strategically target preventions and interventions and help reduce the consequences in adult life,” explained professor Ian Goodyer from University of Cambridge.

“This new biomarker suggests that we may be able to offer a more personalised approach to tackling boys at risk for depression,” added first author Matthew Owens from University of Cambridge.

The researchers measured levels of cortisol in saliva from two separate large cohorts of teenagers.

The first cohort consisted of 660 teenagers, who provided four early morning samples on schooldays within a week and then again 12 months later.

The researchers were able to show within this cohort that cortisol levels were stable over one year in the population at large in both boys and girls.

A second cohort, consisting of 1,198 teenagers, provided early morning samples over three school days.

The researchers hope that having an easily measurable biomarker would enable primary care services to identify boys at high risk, concluded the study published in the Proceedings of the National Academy of Sciences.