Newly released data from the Pentagon reveals that mental illness hospitalized the most servicemembers and veterans at military medical centers in 2012. Post-traumatic stress disorder, substance abuse and other mental illnesses were among the leading causes for the hospitalizations. 

USA Today reports that some servicemembers suffering from mental illness remained in a military hospital for more than a month. The only patients who reported longer stays were amputees. Pentagon data also reveals that servicemembers coping with severe mental illness account for the most lost workdays than any other disease or injury, the news source reports. 

About 20 percent of Iraq and 11 percent of Afghanistan veterans currently suffer from PTSD, according to the National Institute of Health. The PTSD rate is highest among Gulf War-era II veterans, though about 30 percent of Vietnam servicemembers are afflicted with the mental illness.

The institution also states that PTSD is often linked to mild or moderate traumatic brain injury, which is triggered by blast waves rattling the brain inside the skull. According to data compiled by the Department of Defense, more than 30,000 servicemembers were diagnosed with a traumatic brain injury in 2012. 

Defense officials stated to USA Today that both the decade-long wars and the stigma of mental illness are the most likely causes for the high hospitalization rates. 

"The increase in mental health hospitalizations is most likely influenced by exposure of servicemembers to stressful events associated with deployment," Army Lt. Col. Catherine Wilkinson, a spokeswoman for Pentagon health affairs, told the news outlet.