Dr. Charles Marmar of the New York University's Langone Medical Center, in collaboration with the San Francisco VA Medical Center and the University of California, San Francisco, assessed 296 police recruits during academy training for salivary cortisol at first awakening and after 30 minutes.
The difference between the two levels is known as cortisol awakening response. The study found the greater cortisol awakening response during academy training predicted greater peritraumatic dissociation and acute stress disorder symptoms over the first three years of police service.
Police academy recruits who showed the greatest rise in cortisol after waking up were more likely to show post-traumatic stress disorder in response to trauma years later as police officers, Marmar said.
"This study is significant as a potential indicator in determining when people may exhibit stress symptoms in the future," Marmar said in a statement.
"Few studies have prospectively examined the relationships among pre-exposure hypothalamic-pituitary-adrenal activity, acute stress reactions and PTSD. The findings may lead us to new insights on how to identify those who are at a higher risk of PTSD."
The study is to be published in Biological Psychiatry.
Notable deaths of 2014 [PHOTOS]