Teenage boys who have both depressive symptoms and the stress hormone cortisol are about 14 times more likely to develop major depression than those who do not.

Researchers identified the first biomarker ("a biological signpost") for major depression; the finding could help catch the condition in its early stages, a Wellcome Trust news release reported.

"Depression is a terrible illness that will affect as many as ten million people in the [U.K.] at some point in their lives," Professor Ian Goodyer from the University of Cambridge, who led the study, said in the news release. "Through our research, we now have a very real way of identifying those teenage boys most likely to develop clinical depression. This will help us strategically target preventions and interventions at these individuals and hopefully help reduce their risk of serious episodes of depression and their consequences in adult life."

"This new biomarker suggests that we may be able to offer a more personalized approach to tackling boys at risk for depression. This could be a much needed way of reducing the number of people suffering from depression, and in particular stemming a risk at a time when there has been an increasing rate of suicide amongst teenage boys and young men," Doctor Matthew Owens from the University of Cambridge, first author on the study, also said in the news release.

The team measured cortisol levels in the saliva of two large cohorts of teens. One of the cohorts was split into four groups; Group 1 had normal morning cortisol levels and low symptoms of depression over time while Group 4 had high morning cortisol levels and depressive symptoms.

The team found the study subjects in group 4 were about seven times more likely to develop clinical depression and 14 times more likely to suffer from major depression than those in Group 1.