The suicide rates for middle-aged U.S. residents jumped 20 percent, while the suicide rates for teenagers increased only by 2 percent from 1999 to 2004, The New York Times said Tuesday.

Suicide rates for men in the middle-age group increased about 15 percent and for woman about 29 percent in the five-year period. There were more than U.S. suicides in 2004.

Experts say there is a "social-bias" as much of the suicide prevention efforts focus on youth prevention programs. Dr. Eric Caine, a leading suicide prevention official, said there is no "psychological autopsy" making the reasons behind the spike in suicide rates difficult to assess.

U.S. health officials, however, point to the rampant use and abuse of prescription and illegal drugs as the cause for at least a portion of the increased suicide rates.

Other health officials say the increased rate among middle-aged woman may be linked to the drop in the use of hormone replacement therapy in the post-menopausal years.

A study in 1989, however, seems to offer a more general explanation for the rise, saying the changing shape of the U.S. social structure, with family and friends increasingly on the move, disrupts the social support networks of those in the baby boom generation.