After a decade-long decrease, U.S. suicide rates have started to rise, largely because of an increase in suicides among middle-aged white men and women.

If the economy continues to decline, suicides could go up, researchers say.

White people age 40 to 64 have "recently emerged as a new high-risk group for suicide," according to the study in the American Journal of Preventive Medicine.

Suicides increased between 1999 and 2005 by about 3 percent annually in white men and 4 percent in white women age 40 to 64, according to Susan Baker, M.P.H., of the Johns Hopkins Bloomberg School of Public Health in Baltimore, Maryland, and her colleagues. Suicide rates remained the same in Asians and Native Americans, and declined in blacks.

Overall, the suicide rate rose in the early 1980s, then dropped each year from 1986 to 1999. From 1999 to 2005, however, the rates have increased 0.7 percent annually.

In all, 32,637 people killed themselves in the United States in 2005, a rate of 11 per 100,000 people.

Guns are the most common method of suicide, but their use has declined over time. Suicide by hanging or suffocation has increased among both men and women.

The reason for the increase is unknown. But if economic conditions continue to decline, suicides could go up. "This is a concern, especially when one looks at the high rates during the Great Depression," says Baker. Health.com: How exercise can improve your mood

Seetal Dodd, Ph.D., a senior fellow at the University of Melbourne in Australia, has found that suicide rates tend to fluctuate with the economic trends -- at least in men.

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The study is cause for concern, Dodd says, because it identifies middle-aged white men as the new high-risk group for suicide -- the same section of the population at risk for suicide during an economic downturn.

"There is a considerable risk that the current economic situation may result in a further spike in the suicide rate for men of working age, especially if we start to see an increase in unemployment and a decrease in housing affordability and consumer sentiment," Dodd says.

Robert Bossarte, Ph.D., assistant professor of psychiatry at the University of Rochester in New York, says that people have traditionally focused on suicide prevention in the very young and the old, but not necessarily the middle-aged. Historically, people over 65 have had the highest suicide rates, but this study suggests that trend is changing. Health.com: The risk of suicide for bipolar patients

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"The most important take-home message is try to understand what's unique about the [middle-aged] population and what message would be most effective at preventing this," he says.

A number of factors could be affecting the middle-aged, including taking care of aging baby-boomer parents, or coping with substance abuse or unemployment.

Bossarte also notes that while rates are rising in women, men are at greater risk overall. Health.com: Bipolar disorder is different for women

"There's something unique about the life circumstances of white, middle-aged males that is contributing to this risk," he says. "The key is getting people into treatment and getting people to use the resources that are available to them." Health.com: Expert advice on paying for talk therapy

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