Consistently low salivary levels of the stress hormone cortisol in boys aged 7 to 12 are associated with early onset and persistence of extremely aggressive behavior report researchers from the University of Chicago in the Archives of General Psychiatry.
In a four-year study of boys with behavioral problems, those with consistently low cortisol levels began antisocial acts at a younger age, exhibited three times the number of aggressive symptoms, and were three times as likely to be singled out by their classmates as mean or combative as those who had higher or fluctuating cortisol concentrations.
The finding may help psychiatrists better understand differences between adolescent males undergoing a short-term dalliance with delinquent behavior and those with severe and lasting conduct disorder, which is notoriously difficult to treat. Children with persistent conduct disorder tend to remain disruptive for decades and account for a hugely disproportionate percentage of total crimes and violent acts.
The finding also suggests that there is a "lasting biological and not just parental or short-term environmental component to this type of chronic antisocial behavior," said Keith McBurnett, Ph.D., assistant professor of psychiatry at the University of Chicago and lead author of the study. "Children with persistent conduct disorder may have genes that predispose them to produce certain hormones differently, or their hormone production may have been altered before or soon after birth."
For four years, the researchers followed 38 boys who had been referred to a psychiatric clinic for disruptive behavior. They collected saliva samples from each boy in years two and four of the study. Through psychiatric evaluations and interviews with parents and teachers, the researchers assessed the boys' aggressive behaviors and tallied symptoms such as starting fights, using weapons, being cruel to people or animals, stealing, or forcing sexual acts.
Each child in the study was also evaluated by his peers at school; classmates were asked to rate all their fellow students on several behavioral categories, including naming the three boys in class who were meanest, and fought most.
The researchers found that salivary cortisol levels were "strongly and inversely related to aggressive conduct disorder, peer aggression nominations and oppositional defiant disorder." The 12 children with low cortisol levels on both samples averaged 5.2 symptoms of conduct disorder, compared to 1.5 such symptoms in the 26 boys who had a higher level on either sample. More than one third of boys with low cortisol were nominated by their peers as the "meanest" in the class, compared with 10.5 percent of boys who had at least one higher cortisol reading.
Eleven of the 12 boys with consistently low cortisol developed aggressive symptoms before age ten. Less than half of those with at least one higher cortisol level showed symptoms before age ten.
The groups with low, varied or high cortisol levels all had similar IQs, socioeconomic and ethnic characteristics.
Although the mechanism connecting cortisol levels to aggressive behavior is unclear, McBurnett suspects that variation in levels may serve as a marker for abnormalities in the production of various stress hormones that influence the body's response to a challenge or confrontation.
Cortisol is secreted in response to stressful or threatening situations. Low levels may indicate how these young males will respond to potentially stressful situations, suggests McBurnett. "Boys with consistently lower cortisol levels may not be as afraid of retribution," he suggested. "In many aggressive children, the system that responds to the threat of punishment does not react normally. They may not feel stress in the same way and so they don't avoid stressful situations."
Other researchers contributing to this report include Benjamin Lahey, Ph.D., and Paul Rathouz, Ph.D., of the University of Chicago, and Rolf Loeber, Ph.D., of the University of Pittsburgh and Free University, Amsterdam, the Netherlands. Support for the research was provided by the National Institutes of Health.
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