The trend was most pronounced among white men and women in that age group. Their suicide rate jumped 40 percent between 1999 and 2010.
But the rates in younger and older people did not change. And there was little change among middle-aged blacks, Hispanics and most other racial and ethnic groups.
Why did so many middle-aged whites take their own lives?
One theory suggests the recession caused more emotional trauma in whites, who tend not to have the same kind of church support and extended families that blacks and Hispanics do. Another theory notes that white baby boomers have always had higher rates of depression and suicide, and that has held true as they've hit middle age.
"Some of us think we're facing an upsurge as this generation moves into later life," said Dr. Eric Caine, a suicide researcher at the University of Rochester.
During the 1999-2010 period, suicide went from the eighth leading cause of death among middle-aged Americans to the fourth, behind cancer, heart disease and accidents.
The Centers for Disease Control and Prevention released the report, which was based on death certificates. People ages 35 to 64 account for about 57 percent of suicides.
During the period studied, the suicide rate for whites ages 35 to 64 spiked from about 16 suicides per 100,000 people to 22 per 100,000.
Suicide prevention efforts have tended to concentrate on teenagers and the elderly, but research over the past several years has begun to focus on the middle-aged. The new CDC report is being called the first to show how the trend is playing out nationally and to look in depth at the racial and geographic breakdown.
The suicide rate registered a statistically significant increase in 39 out of 50 states. The West had the highest suicide rate.
The report also unveiled surprising information about how middle-aged people kill themselves. Health officials have focused for years on drug overdoses, which are the most common manner of suicide attempt. But overdoses often don't result in deaths.
In the new report, hangings overtook drug overdoses among the middle-aged, becoming the second leading manner of death. But guns remained far in the lead and were the instrument of death in nearly half of all suicides in that age group in 2010.
The economy was in recession from December 2007 until June 2009. Even well afterward, polls showed most Americans remained worried about weak hiring, a depressed housing market and other problems.
CDC report: http://www.cdc.gov/mmwr
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