Twice as many people committed suicide from 2000 to 2002 in the 15 states with the highest rates of gun ownership, compared with the six states where guns are least common, according to the study published in the April issue of the Journal of Trauma. The population in both groups was about the same, the study said.

Hawai'i was among the six states where gun ownership is least common.

Suicide is the eighth leading cause of death among U.S. men, according to the Centers for Disease Control and Prevention's Web Site. The higher suicide rates in the Harvard study were found in men, women and children of all ages in states where more households have guns.

"We found that where there are more guns, there are more suicides," said Matthew Miller, assistant professor of health policy and management at Harvard School of Public Health, in a statement. Miller was lead author of the study.

Miller and colleagues used survey data to estimate gun ownership in all 50 states and looked for a relationship with suicide. The researchers controlled for other factors such as poverty, urbanization, unemployment, drug and alcohol abuse, and mental illness.

More Lethal

Suicide attempts with firearms are much more likely to be fatal than other means, according to the study. Though lethal self-inflicted gunshot wounds make up just 5 percent of all suicide attempts, more than 90 percent of such cases are fatal, the researchers said. That compares with a fatality rate of less than 3 percent for drug-related suicides, which constitute about 75 percent of all attempts.

More than half of the 32,439 Americans who committed suicide in 2004 used a gun, according to the study. Suicides by other means weren't significantly associated with rates of gun ownership, the research showed. The study didn't address whether some people buy guns with the specific intent to commit suicide.

Researchers recommended that guns either be removed from the home or stored securely and separately from ammunition.

"Removing firearms may be especially effective in reducing the risk of suicide among adolescents and other potentially impulsive members of the home," Miller said in the statement.

The research was sponsored by the Chicago-based Joyce Foundation, which supports programs in the region on topics including the environment, education and public welfare. The foundation's projects have included research on preventing violence with firearms.

The six states in the study with the lowest rates of gun ownership were Hawai'i, Massachusetts, Rhode Island, New Jersey, Connecticut and New York.