Interleukin-6 as a predictor of symptom resolution in psychological distress: a cohort study
Virtanen M., Shipley MJ., Batty GD., Hamer M., Allan CL., Lowe GD., Ebmeier KP., Akbaraly TN., Alenius H., Haapakoski R., Singh-Manoux A., Kivimäki M.
Background. Elevated levels of interleukin-6 (IL-6) have been associated with the development of common mental disorders, such as depression, but its role in symptom resolution is unclear. We examined the association between IL-6 and symptom resolution in a non-clinical sample of participants with psychological distress. Method. Data on serum IL-6 were collected at three time points (1991-3, 1997-9, 2002-4) and psychological distress (the 30-item General Health Questionnaire, GHQ-caseness) at five points (1991-3, 1997-9, 2002-4, 2006, 2007-9). A total of 2419 GHQ-cases (aged 39-72 years) at the 3 baseline IL-6 examinations were followed up for symptom resolution in the subsequent examinations of GHQ (mean follow-up 6.5 years). Results. Relative to high IL-6 levels, low levels at baseline were associated with symptom resolution at follow-up (age- and sex-adjusted risk ratio [RR] =1.15, 95% confidence interval 1.06-1.25). Further adjustment for covariates had little effect on the association. Symptomatic participants with repeated low IL-6 were more likely to be symptom-free at follow-up compared with those with repeated high IL-6 (RR=1.21, 95% confidence interval 1.03-1.41). Among the symptomatic participants with elevated IL-6 at baseline, IL-6 decreased along with symptom resolution. Conclusions. IL-6 is potentially related to the mechanisms underlying recovery from symptoms of mental ill health. Further studies are needed to examine these mechanisms and to confirm the findings in relation to clinical depression.