New research led by King’s College London may have found an important clue to understanding how chronic fatigue syndrome (CFS) begins. According to the team’s work, an exaggerated immune response can trigger long-lasting fatigue.

For the study, published in Psychoneuroendocrinology, the researchers tracked 55 people who were following a treatment with interferon-alpha, which is used to fight hepatitis C. Some people on this treatment develop CFS-like symptoms that can last up to six months, thus making it a good test-case to try to isolate factors that can start the condition.

CFS tends to be diagnosed quite late, so it is difficult to pinpoint its cause. Many people suffering from CFS have reported that it began after a major infection. For this reason, the team tracked immune system markers as well as the fatigue level of the patients before, during, and after treatment.

Out of the 55 people tested in the study, 18 developed CFS-like symptoms. Researchers discovered that the immune response in those 18 people was higher than the rest of the patients, even before the beginning of the treatment. But when CFS-like symptoms developed, the immune system markers had returned to their regular level.

“For the first time, we have shown that people who are prone to develop a CFS-like illness have an overactive immune system, both before and during a challenge to the immune system. Our findings suggest that people who have an exaggerated immune response to a trigger may be more at risk of developing CFS,” lead researcher Dr Alice Russell said in a statement.

People living with CFS don’t exhibit any increase in immune response, supporting the hypothesis that the connection is at the beginning. The team compared the immune system activation of 54 people diagnosed with CSF and 57 healthy controls without finding any difference.

“A better understanding of the biology underlying the development of CFS is needed to help patients suffering with this debilitating condition. Although screening tests are a long way off, our results are the first step in identifying those at risk and catching the illness in its crucial early stages,” senior researcher Professor Carmine Pariante added.

The study is currently the most detailed investigation of the links between CFS-like symptoms and the immune system. Further research is necessary to understand if the findings can be equally applied to CFS and to work out what factors lead to an exaggerated immune response.