Chronic fatigue syndrome, an ailment of unknown cause, may be tied to childhood abuse, according to psychologists at Emory University in Atlanta.

Their research found that adults who reported having suffered sexual, emotional or physical abuse or neglect as children were six times more likely to have the syndrome, characterized by extreme tiredness that isn't helped by rest. The study, sponsored by the U.S. Centers for Disease Control and Prevention, appears in today's Archives of General Psychiatry.

More than one million people in the U.S. have chronic fatigue syndrome, according to the Atlanta-based CDC. There are no specific tools to diagnose the condition. Experiences during childhood while the brain develops can affect the way the body reacts to stress later in life, the researchers said.

"Trauma that occurs at different times in childhood may be linked to different long-term changes," said the lead author, Christine Heim, an associate professor of psychology and behavioral sciences at Emory, in a statement. "It's an area in which more work is needed. CFS may be part of a spectrum of disorders associated with childhood adversity, which includes depression and anxiety disorders."

The researchers looked at data from 113 people with the syndrome and 124 who didn't have the condition, in Georgia. The participants were asked to complete questionnaires about five different childhood traumas, including sexual, emotional and physical abuse, and physical and emotional neglect.

Trauma and Fatigue

"Sixty-six people with chronic fatigue said they suffered moderate to severe trauma as children compared with 29 in the control group. Those who experienced sexual and emotional abuse and emotional neglect had the highest risk of developing chronic fatigue syndrome," Heim said in a Jan. 2 telephone interview.

Patients who had childhood trauma and suffered from post traumatic stress disorder, including flashbacks and nightmares, had a ninefold increased risk of chronic fatigue syndrome, she said.

Today's results support earlier findings from a smaller 2006 study in Wichita, Kansas, Heim said.

Researchers also took saliva samples to record levels of cortisol, a hormone that helps regulate the body's response to stress. Those who suffered from childhood trauma had low levels of cortisol.

"The study indicates that low cortisol levels may actually reflect a marker for the risk of developing CFS rather than being a sign of the syndrome itself," she said. "When looking at CFS cases with and without histories of childhood trauma, only those with childhood trauma had the classic low cortisol levels often seen in CFS cases."

Cortisol and Stress

When a person experiences stress, the body releases cortisol to help it to relax. If there isn't enough cortisol, that could cause altered or prolonged responses to stress, which can lead to fatigue and pain, researchers said.

"If cortisol is missing, the body and brain might not be optimally adapting to stress," she said.

Chronic fatigue syndrome is diagnosed when patients have experienced extreme fatigue for at least six months. The condition is marked by a relapse of symptoms after mental or physical exertion, sleep that doesn't refresh, and joint and muscle pain. Women are more at risk then men in developing the condition, and CFS is most common in people in their 40s and 50s, according to the CDC.

Less than 20 percent of chronic fatigue patients in the U.S. have been diagnosed, according to CDC estimates.