New research on posttraumatic stress disorder (PTSD) in soldiers challenges popular assumptions about the origins and trajectory of PTSD, providing evidence that traumatic experiences in childhood -- not combat -- may predict which soldiers develop the disorder.

Psychological scientist Dorthe Berntsen of Aarhus University in Denmark and a team of Danish and American researchers wanted to understand why some soldiers develop PTSD but others don't. They also wanted to develop a clearer understanding of how the symptoms of the disorder progress.

"Most studies on PTSD in soldiers following service in war zones do not include measures of PTSD symptoms prior to deployment and thus suffer from a baseline problem. Only a few studies have examined pre- to post-deployment changes in PTSD symptoms, and most only use a single before-and-after measure," says Berntsen.

The team aimed to address these methodological issues by studying a group of 746 Danish soldiers and evaluating their symptoms of PTSD at five different timepoints. Their study is published in Psychological Science, a journal of the Association for Psychological Science.

Five weeks before the soldiers were scheduled to leave for Afghanistan, they completed a battery of tests including a PTSD inventory and a test for depression. They also completed a questionnaire about traumatic life events, including childhood experiences of family violence, physical punishment, and spousal abuse.

During their deployment, the soldiers completed measures related to the direct experience of war: perceptions of war zone stress, actual life-threatening war experiences, battlefield wounds, and the experience of actually killing an enemy.

The researchers continued to follow the soldiers after their return home to Denmark, assessing them a couple weeks after their return, two to four months after their return, and seven to eight months after their return.

What Berntsen and her colleagues found challenges several widely held assumptions about the nature of PTSD.

Rather than following some sort of "typical" pattern in which symptoms emerge soon after a particularly traumatic event and persist over time, Berntsen and colleagues found wide variation in the development of PTSD among the soldiers.

The vast majority of the soldiers (84%) were resilient, showing no PTSD symptoms at all or recovering quickly from mild symptoms.

The rest of the soldiers showed distinct and unexpected patterns of symptoms. About 4% showed evidence of "new-onset" trajectory, with symptoms starting low and showing a marked increase across the five timepoints. Their symptoms did not appear to follow any specific traumatic event.

Most notably, about 13% of the soldiers in the study actually showed temporary improvement in symptoms during deployment. These soldiers reported significant symptoms of stress prior to leaving for Afghanistan that seemed to ease in the first months of deployment only to increase again upon their return home.

What could account for this unexpected pattern of symptoms?

Compared to the resilient soldiers, the soldiers who developed PTSD were much more likely to have suffered emotional problems and traumatic events prior to deployment. Childhood experiences of violence, especially punishment severe enough to cause bruises, cuts, burns, and broken bones actually predicted the onset of PTSD in these soldiers. Those who showed symptoms of PTSD were more likely to have witnessed family violence, and to have experienced physical attacks, stalking or death threats by a spouse. They were also more likely to have past experiences that they could not, or would not, talk about. And they were less educated than the resilient soldiers.

According to Berntsen and colleages, all of these factors together suggest that army life -- despite the fact that it involved combat -- offered more in the way of social support and life satisfaction than these particular soldiers had at home. The mental health benefits of being valued and experiencing camaraderie thus diminished when the soldiers had to return to civilian life.

The findings challenge the notion that exposure to combat and other war atrocities is the main cause of PTSD.

"We were surprised that stressful experiences during childhood seemed to play such a central role in discriminating the resilient versus non-resilient groups," says Berntsen. "These results should make psychologists question prevailing assumptions about PTSD and its development."