According to researchers in the U.S. children who suffer severe stress may also suffer damage to their brains.
The researchers at the Stanford University School of Medicine and Lucile Packard Children's Hospital have found that children with post-traumatic stress disorder and high levels of the stress hormone cortisol were likely to experience a decrease in the size of the hippocampus - a part of the brain essential for memory processing and emotion.
Similar effects have been seen in animal studies, but this is the first time the findings have been replicated in children.
In order to better understand how stress affects brain development the researchers focused on children living in extreme situations.
Child psychiatrist Dr. Victor Carrion, says traumatic stress is not about stress over homework or fighting with parents, but as a result of undergoing physical, emotional or sexual abuse, witnessing violence or experiencing lasting separation and loss.
Such children says Dr. Victor Carrion, feel as though they are 'stuck in the middle of a street with a truck barreling down at them'.
Dr. Carrion is an assistant professor of child and adolescent psychiatry at the medical school and director of Stanford's early life stress research program; he and his collaborators suggest that cognitive deficits arising from stress hormones, interfere with psychiatric therapy and prolong symptoms.
The children in the study were suffering from post-traumatic stress disorder, or PTSD, which often impairs the child's ability to reach social, emotional and academic milestones.
Carrion says some children are more resilient than others, and it is unclear what the long-term effects of extreme stress are other than that such children have a higher risk of developing depression and anxiety as adults.
One theory suggests that everyone carries an ongoing stress burden that accumulates throughout life and once a certain threshold is reached, either through one or two very traumatic events or through chronic, high levels of stress, adults and children can begin to exhibit PTSD symptoms such as re-experience including flashbacks, intrusive thoughts or nightmares, avoidance and emotional numbing, and physiological hyperarousal such as an elevated resting heart rate.
These behavioural symptoms make PTSD difficult to differentiate from other conditions such as attention deficit/hyperactivity disorder.
The researchers say that children predisposed by genetics or environment to be more anxious than their peers are also more likely to develop PTSD in response to emotional trauma, perhaps because their responses to other life experiences simply left them closer to that threshold than less-anxious children.
For the study the researchers examined 15 children from ages 7 to 13 suffering from PTSD and began by measuring the volume of the hippocampus at the beginning and end of the 12- to 18-month study period.
After corrections for gender and for physiological maturity were done, they found that children with more severe PTSD symptoms and higher bedtime cortisol levels, which is another marker of stress, at the start of the study were more likely to have reductions in their hippocampal volumes at the end of the study than their less-affected, but still traumatized peers.
The researchers found the fact that the change in the hippocampal volume corresponded to both PTSD symptom severity and increased cortisol levels, significant.