The report, funded by the Forces and written by military staff, found that eight per cent of personnel who deployed between 2001 and 2008 were found to have post-traumatic stress disorder, or PTSD.
Another 5.5 per cent of that group developed other depressive disorders as a result of their service in the conflict that was marked by gruelling combat — a feature that considerably increased the risk of a mental health disorder.
"Deployment to Kandahar was associated with a particularly high risk — it was almost six times the risk associated with deployment to the United Arab Emirates or Arabian Gulf," says the report, published Tuesday in the Canadian Medical Association Journal.
The research included 30,500 personnel who deployed in support of the Afghan mission from October 2001 to the end of 2008, and used the medical records of a random sample of about 2,000 of those. The study population was made up of mostly men under the age of 40 in the regular force.
One of the report's authors, Mark Zamorski of the Forces's Directorate of Mental Health, said the risk of a mental health problem appeared to be greater among junior non-commissioned personnel than officers, but didn't elaborate on the reasons for that.
A Defence spokeswoman said none of the authors was available to comment on the findings.
The report restates previous findings in a 2011 military study that estimated eight per cent of personnel deployed to Afghanistan were diagnosed with PTSD within five years after their return.
It's not clear where the numbers place Canadian military members in relation to their international colleagues. The U.S. Department of Veterans Affairs estimates that PTSD afflicts 11 per cent of Afghan veterans and 20 per cent of Iraqi war veterans.
But some say the Canadian military's findings don't reflect the true number of personnel suffering from mental health disorders, since many conceal their problems and the study doesn't include people serving in the last few years of the mission.
Greg Woolvett, whose son suffers from PTSD linked to two tours in Afghanistan, said he thinks the numbers capture only a small fraction of people with so-called operational stress injuries and that the services for them are woefully lacking.
"I would suspect that that figure is inaccurate in its totality," he said in an interview in Burlington, Ont. "There's probably double that amount who have PTSD but who have not come forward."
Woolvett removed his son, Jon, from Canadian Forces Base Petawawa to find him help for a drinking problem and the pain of seeing many of his friends killed in action. He said there's too much of a disconnect between the chain of command and the military's medical personnel, preventing soldiers from getting the care they need.
"They are not connected in terms of how to go about handling these soldiers who have PTSD," he said. "The Canadian Forces, for all of their expertise in training them to be killers, has no real solid defence for PTSD."
Peter Stoffer, the NDP veterans affairs critic, said he also thinks the numbers are higher because members are reluctant to reveal their health problems, fearing they could be stigmatized or face medical release.
"I look at 13.5 per cent and I go, 'Come on, it's got to be higher than that,'" he said. "These are the ones they know about and a fair number of these individuals may not have come forward yet."
The report said less than a third of the group used Forces mental health services during the follow-up period, which averaged four years. The authors say the cohort will be followed as a way of evaluating the care they receive.
Paloma Aguilar, a spokeswoman for Defence Minister Peter MacKay, said in an email that the federal government is committed to ensuring that military personnel benefit from the best health care services available.
Canada's combat and training missions in Afghanistan have claimed the lives of 158 military personnel.