The reason why cortisol, the so-called stress hormone, seems to behave in contradictory ways in children has been discovered by scientists.
Some youngsters with behavioral problems have abnormally high levels of cortisol, while others with identical problems have abnormally low levels.
Now, researchers may have resolved the cortisol paradox.
In a groundbreaking study, researchers at Concordia University and the Centre for Research in Human Development have linked cortisol levels not simply to behavior problems, but to the length of time individuals have experienced behavior problems.
"We studied the relationship between cortisol levels in young people with problematic behaviour such as aggression or depression, and the length of time since the onset of these behaviours," explained Paula Ruttle, lead author and PhD candidate at Concordia's Department of Psychology.
"Cortisol levels were abnormally high around the time problem behaviours began, but abnormally low when they had been present for a long time."
To obtain subjects' cortisol levels, researchers analyzed saliva samples taken from 96 young people during early adolescence. They then matched cortisol levels to behavioral assessments taken in childhood and again during adolescence. Problem behaviours were classified as either "internalizing" (depression and anxiety) or "externalizing" (aggression, attentional problems).
Youngsters who developed depression-like symptoms or anxiety problems in adolescence had high levels of cortisol. However, those who developed symptoms earlier had abnormally low cortisol levels.
It was concluded that Cortisol levels go up when individuals are first stressed by depression or anxiety, but then decline again if they experience stress for an extended period.
The study has been published in the journal Hormones and Behavior.