Teenage boys who show a combination of depressive symptoms and elevated levels of the 'stress hormone' cortisol are up to fourteen times more likely to develop major depression than those who show neither trait, according to research funded by the Wellcome Trust.
In a study published today in the Proceedings of the National Academy of Sciences, researchers from the University of Cambridge have identified the first biomarker - a biological signpost - for major, or clinical, depression. They argue that 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 will affect one in six people at some point in their lives. However, until now there have been no biomarkers for major depression; this is believed to be, in part, because both the causes and the symptoms can be so varied.
"Depression is a terrible illness that will affect as many as ten million people in the UK at some point in their lives," says Professor Ian Goodyer from the University of Cambridge, who led the study. "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."
Dr Matthew Owens from the University of Cambridge, first author on the study, adds: "This new biomarker suggests that we may be able to offer a more personalised 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."
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 twelve 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.
Using self-reports about current symptoms of depression collected longitudinally over the twelve months and combining these with the cortisol findings, Professor Goodyer and colleagues were able to divide the teenagers in the first cohort into four distinct sub-groups, ranging from those with normal levels of morning cortisol and low symptoms of depression over time (Group 1) through to those teenagers with elevated levels of morning cortisol and high symptoms of depression over time (Group 4) - this latter group made up one in six (17%) of all subjects. Importantly, the research group replicated exactly these sub groups using the second cohort.
Because the two cohorts gave identical results, Professor Goodyer and colleagues were able to combine them and study the whole sample of 1,858 teenagers for the probability of developing clinical major depression and other psychiatric disorders when followed up 12 to 36 months later.