“Low levels of the stress hormone cortisol marks out children at higher risk of developing chronic fatigue syndrome as adults,” reported the BBC today. It said that if children with low levels of cortisol are exposed to trauma such as sexual abuse, they are six times more likely to develop the condition when older.
Contrary to the impression that might be gained from parts of the news report, this study did not assess cortisol levels in childhood, but only in adults with or without CFS. Although it found that more people who had CFS reported childhood trauma, this does not conclusively prove that trauma itself causes CFS.
This study contributes to knowledge about potential risk factors for CFS, but much more research is needed into the causes of this condition.
Where did the story come from?
Christine Heim and colleagues from the Emory University School of Medicine and Centers for Disease Control and Prevention (CDC) carried out this research. The work was funded by the CDC. The study was published in the peer-reviewed medical journal Archives of General Psychiatry .
What kind of scientific study was this?
This case control study looked at whether experiences of childhood trauma differed between people with chronic fatigue syndrome (CFS) and those without it. The causes of CFS are not known, but several risk factors, including childhood trauma, have been suggested. One theory suggests that trauma in childhood may affect how people respond to stress, and that this could increase the risk of developing CFS. The researchers wanted to investigate this by looking at levels of the hormone cortisol in people with and without CFS. Cortisol is involved in the body’s stress response.
The study involved 113 people with CFS and 124 people without the condition. The participants with CFS were found through a larger population-based survey of CFS carried out by telephone in Georgia, USA between September 2004 and July 2005. In this larger survey, household telephone numbers were randomly selected and called, and one adult aged 18 to 59 years of age (average age 44) from each household was asked to take part.
This survey identified 469 people who had felt fatigued for six months or more, did not feel better after rest, did not report any medical or psychiatric conditions that might explain their fatigue, and who had at least four out of eight typical symptoms of CFS (suspected cases). These people were invited for a clinical interview. Of these, 292 people attended the interview and 113 were confirmed as having CFS, based on standard criteria.
The researchers identified a control group by carrying out clinical examinations on people who were believed to not have CFS and who were matched to the suspected CFS cases in terms of age, gender, race, and where they lived. Of these people, 124 were confirmed as healthy, and acted as controls.
All participants had a psychiatric examination, and the researchers excluded anyone who had certain conditions, such as manic depression (bipolar disorder) or psychosis. The participants then answered a standard questionnaire about childhood trauma, which assessed five areas including emotional and physical neglect, and emotional, physical, and sexual abuse. Each area was assessed using five statements, which the participants rated from “never true” (scoring one point) to “very often true” (scoring five points). Scores for each area of trauma were added together, giving a total that ranged from 5 to 25. People who scored above a specified amount were classed as having had childhood trauma of moderate or greater severity.
The participants’ cortisol levels were measured using samples of their saliva taken immediately upon waking in the morning, and 30, 45, and 60 minutes later. The researchers then compared levels of childhood trauma between the cases and controls. They used statistical methods to look at whether the levels of psychological symptoms reported in a person's psychiatric examination affected the link between childhood trauma and CFS. The researchers also looked at the relationship between cortisol levels, childhood trauma and CFS.
What were the results of the study?
The researchers found that higher levels of childhood trauma were reported by people with CFS than in people without it. About 62% of people with CFS reported childhood trauma in at least one of the five areas, compared with about 24% of those without CFS. Experiencing childhood trauma increased the risk of CFS by 5.6 times. In particular, levels of sexual abuse, emotional abuse and emotional neglect showed the greatest differences between cases and controls, after adjusting for (taking into account) the other areas.
People with CFS showed more mental health symptoms, including depression, anxiety and post-traumatic stress disorder. However, the link between childhood trauma and CFS remained even after adjusting for these symptoms.
The researchers also found that, compared with the controls, people with CFS had lower levels of cortisol when they woke up. If the participants were split into those with and without trauma, only those with CFS and childhood trauma had reduced cortisol levels.
What interpretations did the researchers draw from these results?
The researchers conclude that their results “confirm childhood trauma as an important risk factor of CFS”. They suggest that reduced levels of cortisol, which is a “hallmark feature of CFS, appears to be associated with childhood trauma”. This may indicate the biological mechanism behind how childhood trauma could affect risk of CFS.
They say that their findings “are critical to inform pathophysiological research and to devise targets for the prevention of CFS”.
What does the NHS Knowledge Service make of this study?
This was a relatively small study, which may provide some early evidence of a link between psychological and biological risk factors for CFS. There are some limitations to note, however:
- Although people with CFS reported more childhood trauma, this type of study cannot conclusively prove that the childhood trauma itself “caused” CFS because other factors may be responsible for the apparent link. For example, other illnesses in childhood, abuses outside of the family unit and adult trauma were not considered or adjusted for.
- There may be differences in how individuals rate or recall their experiences of trauma, and this could have affected the results. The authors acknowledge that there may be problems in relying on “retrospective and uncorroborated self reports” of childhood experiences and suggest that simply forgetting the trauma, not disclosing it, or other biases, may have partly accounted for the difference between the groups.
- This study only measured cortisol levels in adults who were already known to have or not have CFS. Therefore it cannot indicate whether cortisol levels in childhood owuld be able to predict risk of CFS in later life. As CFS is relatively rare, this type of test by itself would be unlikely to help identify those at risk.
Although this study cannot prove that childhood trauma itself “causes” CFS, or that childhood cortisol levels can predict CFS in adulthood, this study contributes to knowledge about potential risk factors for CFS. Much more research is needed to fully understand the causes of this complex condition.