The number of suicides among 18- to 29-year-old men increased from 88 in 2009 to 152 in 2011. That translates into a 44% rise in the suicide rate, which jumped to 57.9 suicides per 100,000 veterans.

Experts were at a loss to explain the increase. It occurred as the Department of Veterans Affairs was bolstering its suicide prevention efforts in response to a sharp rise in military suicides during a decade of war in Afghanistan and Iraq.

One possibility is that those efforts have been successful in drawing more suicidal young veterans to the VA for care, but that many still wind up killing themselves.

“If you have more people at risk, the rates are going to change,” said Dr. Timothy Lineberry, a suicide expert at the Mayo Clinic in Rochester, Minn., who was not involved in the analysis.