A study of soldiers who’ve fought in combat highlights three factors that increase the likelihood they will develop post-traumatic stress syndrome.

William Tecumseh Sherman, a general during the Civil War, told the graduating class of the Michigan Military Academy in 1879 that, “There is many a boy here today who looks on war as all glory, but, boys, it is all hell.”

While many men have endured the hell of war and escaped unscathed, young men who experienced personal trauma before service are the most likely to develop lasting mental health issues after serving in combat.

A new study published in the journal Clinical Psychological Science found that soldiers who enlisted before the age of 25 were seven times more likely to develop post-traumatic stress syndrome.

Post-traumatic stress syndrome, or PTSD, is a debilitating condition in which sufferers experience a heightened sense of danger and impending doom following a traumatic experience, such as a natural disaster or a physical assault.

It is the most common condition diagnosed in soldiers returning from war, though during previous conflicts it was known as “shell shock” or “battle fatigue.”

Veterans’ mental health is an increasingly pressing issue, with an estimated 2.4 million U.S. soldiers fighting or returning from tours in Iraq or Afghanistan.

Researchers at Columbia’s Mailman School of Public Health and the New York State Psychiatric Institute examined data from 260 Vietnam War veterans to determine what effect, if any, certain factors had on a soldier’s risk of developing PTSD.

They focused on three mitigating factors:

  • severity of combat exposure (i.e. traumatic combat events)
  • pre-war vulnerabilities, such as childhood abuse or a family history of substance abuse
  • involvement in harming civilians or prisoners of war

The researchers found that exposure to stressful combat situations was present in 98 percent of the cases of PTSD, but that it wasn’t enough to cause the symptoms on its own. Thirty percent of soldiers who endured trauma during a tour still didn’t develop PTSD.

However, add in the other two factors—problems in childhood and harming the innocent—and a veteran had a 97 percent chance of developing PTSD following combat.

“While severity of combat exposure was the strongest predictor of whether the soldiers developed the syndrome, pre-war vulnerability was just as important in predicting the persistence of the syndrome over the long run,” the study authors said. “Given the seemingly potent interaction between combat exposure and pre-war vulnerability, these results emphasize the need to keep the more vulnerable soldiers out of the most severe combat situations.”

Though the recent study focused on Vietnam veterans, there is ongoing research into the effectiveness of pre-enlistment mental health screenings and follow-ups once the soldiers begin to serve. Unfortunately, many returning veterans encounter major barriers to proper mental health care after their tours.

In 2011, a study in the American Journal of Psychiatry highlighted the importance of pre-deployment mental health screenings.

In studying 21,000 soldiers form Fort Stewart, Ga., researchers found that soldiers who didn’t receive mental health screenings were four times more likely to have mental health problems during combat and were twice as likely to report suicidal thoughts or to be airlifted out of battle for mental health reasons.

The screenings also helped determine which soldiers weren’t fit for combat and those who should serve on restricted duty.

Considering that the U.S. has been at war for 214 years since 1776, it’s nice to know that the mental health of the young men and women who serve our country is slowly gaining the attention it deserves.