National Guard and Reserve combat troops in Iraq and Afghanistan are more likely to develop drinking problems than active-duty soldiers, a new military study suggests.

The authors speculate that inadequate preparation for the stress of combat and reduced access to support services at home may be to blame.

The study, appearing in Wednesday's Journal of the American Medical Association, is the first to compare Iraq and Afghanistan veterans' alcohol problems before and after deployment.

It should help guide planning for future prevention and treatment programs, said study co-author Dr. Edward Boyko, who works for the Veterans Affairs Puget Sound Health Care System.

The research is one of the first major studies to emerge from the Pentagon's landmark "Millennium" study, launched in 2001 because of concerns about possible health effects from the first Gulf War. It includes tens of thousands of military personnel and is designed to evaluate the long-term health effects of military service.

In the alcohol study, researchers analyzed data from nearly 80,000 military personnel, including more than 11,000 who were sent to Iraq and Afghanistan. They looked at whether deployment and combat exposure were linked with new alcohol problems such as binge drinking.

They found that more than 600 combat troops who reported no binge drinking at the start of the study developed the problem after deployment and combat exposure. That accounted for about 26 percent of the estimated 2,400 military personnel exposed to combat who did not report binge drinking at the start of the study

New patterns of regular heavy drinking and alcohol problems, such as missing work because of drinking, occurred more often in guard and reserve troops who experienced combat. Their risk of developing new drinking problems, compared to guardsmen and reservists who weren't deployed, was about 60 percent higher.

Alcohol abuse, post-traumatic stress disorder and depression make up an "unholy trinity" that haunts some combat soldiers, said psychologist William Schlenger of the consulting firm Abt Associates Inc. in Durham, N.C. He was a principal investigator of the influential National Vietnam Veterans' Readjustment Study, but was not involved in the new research.

"They have intrusive recollections: 'I keep remembering it, I have nightmares about it, I can't escape it,"' Schlenger said. Vets try to escape the memories through alcohol or drugs, he said.

The military has leaned heavily on the National Guard and reserves in the current conflict. At certain times in 2005, the guard and reserves made up nearly half the troops fighting in Iraq.

For citizen soldiers, returning from war differs from the return for active-duty soldiers.

"It's not like you live at Fort Hood or Camp Lejeune and everybody on your street is in the military," said Bob Handy, a Vietnam veteran who heads Santa Barbara, Calif.-based Veterans United for Truth, a group that is suing the VA to make changes in mental health care.

The Millennium study will continue to track veterans' health and may determine whether drinking problems among returning combat troops are long-lasting, Boyko said.