FRIDAY, Dec. 28 (HealthDay News) -- Constant worriers are at increased risk for developing post-traumatic stress disorder (PTSD), according to a new study.

Many people experience traumatic events -- such as witnessing violence, being assaulted or the death of a loved one -- but only a few develop PTSD, noted study author Naomi Breslau, a professor of epidemiology at Michigan State University.

People with PTSD feel stressed and fearful after experiencing or seeing a dangerous event long after the danger is over.

"So the question is, 'What's the difference between those who develop PTSD and the majority who don't.' This paper says people who are habitually anxious are more vulnerable. It's an important risk factor," Breslau said in a university news release.

The study included about 1,000 people who answered questions meant to assess their level of neuroticism, which is marked by chronic anxiety, depression and a tendency to overreact to everyday challenges and disappointments.

Over 10 years of follow-up, half of the participants experienced a traumatic event. People who had higher levels of neuroticism at the start of the study were more likely to be among the 5 percent who developed PTSD.

The study was released online in advance of publication in an upcoming print issue of the journal Psychological Medicine.

Breslau pointed out in the news release that "there have been studies of neuroticism and PTSD, but they've all been retrospective," or in other words, looking back in time. This study assessed participants' personalities prior to their traumatic experience. "We're never sure of the order of things in a retrospective study. This study sets it in a clear time order," which makes the findings very persuasive, she said.

While there's not much that can be done to prevent PTSD, these findings may help doctors to identify people at the highest risk and respond accordingly when they experience a traumatic event, Breslau said.

"We need to be concerned about people with previous psychiatric disorders if there's some kind of catastrophe. The main thing is that doctors have to look after their patients, ask them questions and get to know them," she advised.

While the study found an association between chronic worry and development of PTSD, it did not prove a cause-and-effect relationship.

More information

The U.S. National Institute of Mental Health has more about post-traumatic stress disorder.