Middle-aged white people now account for a third of all suicides in the U.S., a new government report shows.

Suicide is the nation's 10th leading cause of death, and the overall rate rose 24 percent in 15 years, according to the report from the Centers for Disease Control and Prevention.

Suicides have long been most common among white people — particularly older white males. But most striking in the new report is the growth in whites ages 45 to 64.

They were a third of suicide deaths in 2014, up from about a quarter in 1999.

"The findings in this report are extremely concerning," said Nadine Kaslow, an Emory University researcher and past president of the American Psychological Association.

The CDC data — released Friday — provides a detailed look at the latest year's suicide statistics, and a broader look at how much the situation has changed over 15 years.

There were nearly 43,000 U.S. suicides in 2014. More than 14,000 of them were middle-aged whites — twice the combined total for all blacks, Hispanics, Asians, Pacific Islanders, American Indians, and Alaska Natives.

In other terms — a group that represents 18 percent of the U.S. population accounted for 33 percent of the suicides.

The CDC also reported striking increases in suicide rates in adult American Indians and Alaska Natives, although the number of those suicide deaths is much smaller.

The report doesn't try to answer why certain trends are occurring. Other experts have speculated that middle age can be a particularly hard time for whites, who — compared to some other racial and ethnic groups — commonly don't have as many supportive relationships with friends, family, or religious communities,

Money was a factor, too, they say. The economy was in recession from the end of 2007 until mid-2009. Even well afterward, polls showed most Americans remained worried about weak hiring, a depressed housing market and other problems.

White people, in particular, seem to expect financial comfort and happiness by middle age — and have difficulty coping when things get worse instead of better, Emory's Kaslow said.

In a report earlier this week, the CDC found that life expectancy for white women — and for white people as a whole — declined slightly in 2014. Some experts have said a combination of factors may be the reason, including more drug overdoses and suicides.