According to the latest research traumatic events in childhood, and stress or emotional instability at any period in life, may be linked to the development of chronic fatigue syndrome (CFS).

CFS is thought to affect between 400,000 and 900,000 U.S. adults and is defined as unexplained fatigue that lasts for at least six months, does not get better with rest and interferes with normal activities.

A formal diagnosis of CFS, necessitates at least four of eight additional symptoms, including extreme fatigue after exertion, difficulties with memory and concentration, poor sleep, headaches, muscle pain, joint pain, sore throat and tender lymph nodes.

Two new studies suggest that CFS and similar illnesses occur when the brain is unable to cope with challenging experiences.

In one study Christine Heim, Ph.D., from the Centers for Disease Control and Prevention (CDC) and Emory University, Atlanta, and colleagues compared 43 individuals with CFS to 60 controls without CFS who were taking part in a large study of Wichita, Kansas, residents.

For the study all participants who were age 50, were given a medical examination and provided their medical history; they were also interviewed to detect psychiatric disorders.

They were then asked to complete a questionnaire that assessed for five types of childhood trauma: emotional, physical and sexual abuse and emotional and physical neglect.

The responses to each item were numbered and added to produce a score for each type of trauma and one overall trauma score.

The CDC team found that those individuals with CFS had higher overall trauma scores than those without CFS, and exposure to trauma appeared to increase the risk of CFS between three and eight times, depending on the type; emotional neglect and sexual abuse during childhood were most strongly associated with CFS.

For each additional type of childhood trauma experienced, the risk of having CRS increased by 77 percent; the risk increased by 6 percent for each additional point increase in total trauma score.

The researchers found that while not all patients with CFS had experienced childhood trauma, those who had tended to have worse symptoms than those who had not.

CFS patients were also more likely to have psychiatric disorders, including depression, anxiety and post-traumatic stress disorder which appeared to be associated with childhood trauma.

The researchers say that CFS seems to be part of a spectrum of disorders that are associated with childhood adversity, which in adulthood frequently manifest or worsen in relation to an acute stress or challenge.

They believe high emotional reactivity is a risk factor for all of these disorders and enhanced stress and mood reactivity is central the disorders.

In the second study, Kenji Kato, Ph.D., of Karolinska Institutet, Stockholm, Sweden, and colleagues, based on data from the Swedish twin registry, also found that stress appeared to be a trigger for developing CFS.

Kato and colleagues looked at data on more than 19,000 twins born in Sweden from 1935 to 1958 and found that emotionally instability was linked to a 72% higher risk of CFS symptoms.

Emotional instability is a personality trait and people affected with it tend to have low self-esteem and feelings of anxiety, depression, and guilt.

But Kato and colleagues found it was only part of the problem, as high levels of stress reported up to 25 years before CFS symptoms appeared, increased CFS risk by 64%.

When the researchers looked only at twins sharing the same genetic makeup, they found that emotional instability no longer predicted CFS, whereas stress upped a twin’s odds of having CFS almost six times.

Kato and colleagues say that while emotional instability is an indirect risk factor for CFS, stress is a direct risk factor.

The two studies are published in the current issue of Archives of General Psychiatry.