TUESDAY, Nov. 7 (HealthDay News) -- Childhood trauma, along with stress or emotional instability at any point in one's life, might be risk factors for chronic fatigue syndrome.

So say two studies in the November issue of the Archives of General Psychiatry.

"We're not talking about a bunch of stressed-out people. We're talking about the biological underpinnings of a real and very debilitating illness," said Dr. Nancy Klimas, a professor of medicine at the University of Miami Miller School of Medicine, who was not involved with either study. "We're trying to remove the stigma of a psychiatric overlay and put it back in biology, where it belongs."

Although intriguing, experts added that the results are preliminary.

"These are interesting elementary papers," said Dr. Charles Goodstein, a psychoanalyst and clinical professor of psychiatry at New York University School of Medicine. "These studies bear out what we have learned in medicine and in psychiatry: Illnesses of all types are determined in large part by an interplay of genetically determined predispositions and environmental factors."

"CFS remains an elusive condition," Goodstein continued. "It seriously incapacitates patients, but physicians are stumped by the lack of objective signs on physical examination."

Some 1 million people in the United States are estimated to suffer from chronic fatigue syndrome (CFS), costing the nation some $9 billion annually, and each family $20,000 a year in lost earnings. The condition is more common in women aged 40 to 59, and is marked by a cluster of debilitating symptoms, including unexplained fatigue, problems sleeping, problems with memory and concentration, and pain.

The illness was first recognized in the late 1980s and, initially dubbed the "yuppie flu," suffered from a credibility crisis. The U.S. Centers for Disease Control and Prevention on Friday unveiled an awareness campaign intended to remedy that problem.

Still, the condition remains a mysterious one and, despite more than 4,000 studies and two decades of research, the cause remains elusive, as do effective treatments.

Anecdotal evidence suggests that stress may be a triggering factor, but there has been little systematic study of the issue.

This new report is part of a larger study undertaken by the CDC, which surveyed the population in Wichita, Kan., over a four-year period from 1997 to 2000.

The authors of the current paper conducted in-depth assessments of 43 people with CFS, comparing them with 60 control subjects, all identified from an initial sample of more than 56,000 adults residing in Wichita. In addition to multiple medical tests, participants completed questionnaires on childhood trauma and psychiatric symptoms such as depression and anxiety. Five different types of childhood trauma were addressed -- sexual, physical, emotional, emotional neglect and physical neglect.

People with CFS reported much higher levels of childhood trauma and psychiatric symptoms, compared with the control participants. In fact, childhood trauma exposure in general was associated with a three-to-eight-fold greater risk for CFS. But emotional neglect and sexual abuse were the most powerful predictors of who would develop CFS. The risk of having CFS increased by 77 percent for each additional type of childhood trauma a person experienced, the researchers found.

Those who had experienced more trauma were more likely to have more severe symptoms of CFS. And those who had other psychiatric symptoms along with childhood trauma were also at greater risk.

"It's important to see that CFS has subgroups," Klimas said. "It's really important not to merge all these observations into one solid, big group."

The information may one day help identify people at risk for chronic fatigue syndrome. "Not all people with CFS had histories of childhood trauma, and not all of the people who had childhood trauma had CFS," explained study author Christine Heim, assistant professor of psychiatry and behavioral sciences at Emory University, in Atlanta. "It's not the whole picture. There must be some sort of resilience, and if we knew what those were, that would be important for prevention."

The second study looked at 19,192 Swedish twins, 1,570 of whom had chronic fatigue syndrome. Twins who experienced emotional instability and stress were more likely to have CFS. Individuals who reported that their life was stressful were 64 percent to 65 percent more likely to develop CFS than people who did not make such a report. Stress increased a twin's risk of developing CVS five-fold.