02/17/2012 12:37 pm ET

Military Service Does Number On Vets' Minds, Study Suggests

Combat seems to do a number on some soldiers' minds--as high rates of post-traumatic stress disorder (PTSD) among returning soldiers attest. But a bombshell new study from Washington University in St. Louis suggests that simply serving in the military can affect veterans in ways that make it hard for them to get along with friends, family, and co-workers in the civilian world.

"Military recruits are a little less warm and friendly to begin with and the military experience seems to reinforce this--as after service, men score even lower on agreeableness when compared to individuals who did not go into the military," lead author Dr. Joshua J. Jackson, an assistant professor of psychology at the university, said in a written statement. "Interestingly, this influence appears to linger long after the soldier has re-entered the workforce or returned to college."

The study confirms that military veterans score lower than their civilian counterparts on tests of "agreeableness." It also indicates that the military tends to attract men who are more aggressive and more interested in competition than other men--and less concerned about the feelings of others, according to the statement.

For the six-year study, the scientists looked at the personality traits of high school students in Germany. The study, published in the journal Psychological Science, showed that young men tended to become more agreeable over the course of the study. But those who went into the military showed smaller increases in agreeability.

Jackson said there could be an upside to being less agreeable. Less agreeable men might be better at climbing the corporate ladder, for example. And there's research suggesting that some veterans may be more likely to volunteer to help others. But, Jackson said, the finding suggests that military service can make relationships more challenging--and offers a new explanation as to why military men tend to differ from their civilian counterparts in rates of divorce, longevity, income, and health problems.