A recent study may shine a light on the development of post-traumatic stress disorder in police officers after the attacks of Sept. 11, 2001.

A group of researchers, including two at the Yale School of Medicine, have released data suggesting that police responders who spent more time at the World Trade Center disaster site both during and following the attack have experienced more severe symptoms of post-traumatic stress disorder. This connection may help to reduce future post-traumatic stress for police officers through preemptive stress management training and other techniques.

“9/11 is one of the biggest human-made disasters of our time,” said Roman Kotov, professor of psychiatry at Stony Brook University and lead author of the study. “The key finding is that the responders who have been more exposed during the cleanup operation have become more sensitive to everyday stressors in years that follow.”

The study attempted to examine the effect of length of direct exposure to the attack on the severity and frequency of PTSD symptoms in its aftermath. The researchers used data from 18,896 disaster responders, collected between 2002 and 2012 by the World Trade Center Health Program, which monitors treatment of 9/11 responders. Nearly half of the participants were law enforcement officials, while others were non-professional responders such as construction workers and electricians.

Each participant was interviewed twice. At the first meeting, researchers ascertained participants’ level of exposure to the disaster, including the amount of time spent at the World Trade Center site and whether they had lost a co-worker or friend in the attack. The follow-up interview attempted to assess the post-disaster stress and its effects on the daily lives of the responders.

After distilling these interviews into quantitative measures, the researchers analyzed the large data set and found statistically significant associations between length of disaster exposure and PTSD for police officers, but not for other responders.

The findings suggest potential steps that could be taken to reduce PTSD in police officers. Focusing on providing stress management and PTSD treatment to officers who spend long periods of time working at a site of past trauma can help to reduce their symptoms, the study concludes.

While the results seem clear, Kotov said that the study could have produced more effective and useful data.

“One big limitation is that we are asking people about this exposure now, more than a decade in some cases after the exposure occurred,” Kotov said. “If we could have interviewed responders about the exposure in 2002, that would’ve been a real improvement over the design that we actually had to follow.”

Additionally, this study answered only one of many questions about PTSD in World Trade Center survivors. Rather than simply focusing on the study’s conclusions as they relate to 9/11 specifically, researchers will attempt to use this study as a stepping-stone to more widespread investigations.

According to Robert Pietrzak, professor of psychiatry at the Yale School of Medicine and a coauthor of the study, the ultimate goal of the research is to develop a risk prediction model that can inform future prevention and treatment efforts for disaster-related PTSD.

Though Pietrzak and his fellow researchers on the study are looking to apply their research to the broader world of disaster-related trauma, Joan Cook, a professor of psychiatry at the Yale School of Medicine who has done extensive research on PTSD in war veterans, said she sees the scope of these findings as limited in application to 9/11. She said she does not see this research as applicable to PTSD treatment for those who have served in war zones.

“Serving in a war-zone can mean constant or multiple times a day exposure to serious life threat,” Cook said. “Some treatments will encourage the person for focus on the ‘worst’ or ‘most disturbing’ traumatic incident.”

Nonetheless, Cook emphasized the importance of these findings, citing the large data set and reliable self-reporting measures as “impressive.”

According to New York City health programs, at least 10,000 civilians and responders have been diagnosed with post-traumatic stress disorder since being exposed to the World Trade Center attack.