Researchers at the University of California, San Francisco and the San Francisco VA Medical Center studied 103,788 veterans and found 31 percent, or 32,010, had been diagnosed with mental health or psychosocial problems, CNN reported.

The most common diagnosis was for post-traumatic stress disorder, which was found in 13,205 veterans. PTSD is an anxiety disorder resulting from exposure to or involvement in traumatic events and can lead to depression, memory and cognitive problems and physical problems.

The authors wrote in the study published in the Archives of Internal Medicine that veterans 18-24 years of age appeared to be at greatest risk.

"Our results signal a need for improvements in the primary prevention of military service-related mental health disorders, particularly among our youngest service members," the authors wrote.