The suicide rate among middle-aged Americans has reached its highest point in at least 25 years, a new government report said Thursday.

The rate rose by about 20 percent between 1999 and 2004 for U.S. residents ages 45 through 54 — far outpacing increases among younger adults, the U.S. Centers for Disease Control and Prevention reported.

In 2004, there were 16.6 completed suicides per 100,000 people in that age group. That's the highest it's been since the CDC started tracking such rates, around 1980. The previous high was 16.5, in 1982.

Experts said they don't know why the suicide rates are rising so dramatically in that age group, but believe it is an unrecognized tragedy.

The general public and government prevention programs tend to focus on suicide among teenagers, and many suicide researchers concentrate on the elderly, said Mark Kaplan, a suicide researcher at Portland State University.

"The middle-aged are often overlooked. These statistics should serve as a wake-up call," Kaplan said.

Roughly 32,000 suicides occur each year — a figure that's been holding relatively steady, according to the Suicide Prevention Action Network, an advocacy group.

Experts believe suicides are under-reported. But reported rates tend to be highest among those who are in their 40s and 50s and among those 85 and older, according to CDC data.

The female suicide rates are highest in middle age. The rate for males — who account for the majority of suicides — peak after retirement, said Dr. Alex Crosby, a CDC epidemiologist.

Researchers looked at death certificate information for 1999 through 2004. Overall, they found a 5.5 percent increase during that time in deaths from homicides, suicides, traffic collisions and other injury incidents.

The largest increases occurred in the 45 to 54 age group. A large portion of the jump in deaths in that group was attributed to unintentional drug overdoses and poisonings — a problem the CDC reported previously.

But suicides were another major factor, accounting for a quarter of the injury deaths in that age group. The suicide count jumped from 5,081 to 6,906 in that time.

In contrast, the suicide rate for people in their 20s — the other age group with the most dramatic increase in injury deaths — rose only 1 percent.