The number of women committing suicide has increased dramatically over the past decade and is driving up the nation's suicide rate as a whole, a new study finds.

The rate of suicide in the United States has risen for the first time in a decade and, for once, middle-age women are being looked at as the culprit driving the increase, according to researchers from the Johns Hopkins Bloomberg School of Public Health’s Center for Injury Research and Policy.

The increase in the overall suicide rate between 1999 and 2005 was due primarily to an increase in suicides among whites ages 40-64, with white middle-age women experiencing the largest annual increase, according to the study, which will be published in the December issue of the American Journal of Preventive Medicine.

The overall suicide rate rose 0.7 percent over the study period, but increased 3.9 percent for middle-age white women and 2.7 percent for white men in the same age group.

“The results underscore a change in the epidemiology of suicide, with middle-aged whites emerging as a new high-risk group,” said study co-author Susan P. Baker, a professor with the Bloomberg School’s Center for Injury Research and Policy, in a news release.

“Historically, suicide prevention programs have focused on groups considered to be at highest risk — teens and young adults of both genders as well as elderly white men," she continued. "This research tells us we need to refocus our resources to develop prevention programs for men and women in their middle years.”

Researchers also found that while firearms remain the predominant method of suicide, the rate of firearm suicides decreased during the study period. Suicide by hanging or suffocation increased markedly with a 6.3 percent annual increase among men, and a 2.3 percent annual increase among women, the authors noted.

Hanging/suffocation accounted for 22 percent of all suicides by 2005, surpassing poisoning at 18 percent, researchers found.

The study's authors said the reasons for the increased suicide rate are not fully understood and that more research is needed.