The act of killing is as fundamental to war as oxygen is to fire. Yet it is also the one thing many combat veterans avoid discussing when they return home, whether out of shame, guilt or a deep fear of being misunderstood.

But a new study of Iraq war veterans by researchers in San Francisco suggests that more discussion of killing may help veterans cope with an array of mental health problems stemming from war.

The study, published last week in The Journal of Traumatic Stress, found that soldiers who reported having killed in combat, or who gave orders that led to killing, were more likely to report the symptoms of post-traumatic stress disorder, alcohol abuse, anger and relationship problems. The study was based on data from health assessments conducted on about 2,800 soldiers who returned from Iraq in 2005 and 2006.

Shira Maguen, a psychologist at the San Francisco Veterans Affairs Medical Center and the principal investigator on the study, said the results suggested that mental health professionals need to incorporate killing more explicitly into their assessments and treatment plans for veterans. That would include finding ways to discuss the impact of killing, in public forums and in private treatment, to reduce the stigma and shame, she argued.