Researchers have found an astonishingly high rate of suicides among US female military veterans six times the rate of other women in the nation.

The rate is even more shocking among young veterans. For women ages 18 to 29, veterans kill themselves at nearly 12 times the rate of non-veterans.

"It's staggering," Dr. Matthew Miller, an epidemiologist and suicide expert at Northeastern University, told the Los Angeles Times. "We have to come to grips with why the rates are so obscenely high."

The female vet suicide rate is very close to the rate for male veterans, which is particularly surprising because men tend to commit suicide far more frequently than women. Most research and statistics have been focused on veteran men, who account for 90% of America's former troops. There were 173,969 adult suicides — men and women, veterans and non-veterans — in 23 states between 2000 and 2010.

For all age groups, female veterans suicide rates are between four to eight time higher than that of other women, going back to the 1950s, indicating that recent wars aren't a particular risk factor.

Researchers found that 40% of the female veterans who committed suicide used guns, compared with 34% of other women.

Researchers don't have a theory for the suicides. They speculate that traumatic events play a role, which may be linked to or exacerbated by sexual assault or intimidation. The Pentagon has estimated that 10% of women in the military have been raped while serving and another 13% have been subject to unwanted sexual contact.

It is also possible the military draws women at a higher suicide risk to begin with. Women volunteers may tend to be bigger risk-takers and experience the worst of war, for example, or something in their background may contribute to their suicides. Some studies have found that men and women who join the military are more likely to have endured difficult childhoods, including emotional and sexual abuse.