The number of middle-aged Americans who have committed suicide has risen sharply in the past decade, federal health officials reported Thursday.

Experts aren't sure why the jump in deaths has occurred, but point to the recession as a possible contributing factor.

According to the U.S. Centers for Disease Control and Prevention, suicides among those aged 35 to 64 have risen by 28 percent since 1999 -- from 13.7 suicides per 100,000 people that year to 17.6 per 100,000 in 2010.

More Americans now commit suicide than are killed in car accidents. In 2010, the CDC reported, 33,687 people died in car crashes, but 38,364 took their own life.

"We have known about this trend for a while now, the CDC is merely documenting it," said Lanny Berman, executive director of the American Association of Suicidology, who was not involved with the report.

Why the rate has risen so dramatically among the middle-aged isn't clear, Berman said. "I and most of my colleagues are dumbfounded to explain it," he said.

"The best we can come up with is maybe this is the group most likely to be affected by the recession and unemployment and [home] foreclosure," Berman said. "It affected suicide rates both nationally and internationally."

What isn't known, however, is how many of those who took their lives were having financial problems, Berman said. Whether the recession is the actual cause will take years to unravel. "All we can guess at now is association," he said.

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