After falling for more than a decade, the U.S. suicide rate has climbed steadily since 1999, driven by an alarming increase among middle-age adults, researchers said Monday.
A new six-year analysis in the American Journal of Preventive Medicine found that the U.S. suicide rate rose to 11 per 100,000 people in 2005, from 10.5 per 100,000 in 1999, an increase of just under 5%.
The report found that virtually all of the increase was attributable to a nearly 16% jump in suicides among people ages 40 to 64, a group not commonly seen as high-risk. The rate for that age group rose to 15.6 per 100,000 in 2005, from 13.5 per 100,000 in 1999.
Susan P. Baker, an epidemiologist at Johns Hopkins University Bloomberg School of Public Health and an author of the study, said she was baffled by the findings. Sociological studies have found that middle age is generally a time of relative security and emotional well-being, she said.
"We really don't know what is causing this," said Dr. Paula Clayton, research director of the American Foundation for Suicide Prevention, who was not involved in the study. "All we have is speculation."
One possibility, she said, is that the increase in suicides might be tied to a concurrent increase in abuse of prescription pain pills, such as OxyContin. Studies have shown that people who abuse drugs are at greater risk for suicide, she noted.
Another possible explanation, she said, was the drop in hormone replacement therapy after it was linked to health risks in 2002. Women who gave up the drugs or decided not to take them might have been more susceptible to depression and potentially suicide, she said.
Dr. Ian Cook, an associate professor of psychiatry and biobehavioral sciences at UCLA's David Geffen School of Medicine, who was not involved in the study, said stresses of modern life, particularly worries in the aftermath of the terrorist attacks of Sept. 11, 2001, might have a role.
Untreated depression is the leading cause of suicide, he said.
"The bottom line is while we can't infer a lot of things about what is causing the trend, I think it cries out for better depression screening and treatment," he said.
Suicide rates declined 18% from 1986 to 1999, helped in part by a focus on prevention among teenagers and the elderly.
In the current study, researchers found little or no change in the suicide rates for three other age groups: 10 to 19, 20 to 29, and over 65.
Suicides for whites ages 40 to 64 rose 17% from 1999 to 2005, researchers said. For middle-age white men, the rate rose 16% to 26.9 per 100,000 in 2005, from 23.1 per 100,000 in 1999. For white women in that age group, the rate rose 19% to 8.2 per 100,000 from 6.9 per 100,000.
The suicide rate among middle-age African Americans rose 7% from 1999 to 2005, but it was not enough to drive up the overall suicide rate among blacks.
For black men ages 40 to 64, the rate rose 5% to 10.4 per 100,000 from 9.9 per 100,000, and for black women in that age group, the rate rose 14% to 2.5 per 100,000 from 2.2 per 100,000.
Baker said she had no idea why the increases among whites were higher.