Inspired by previously published cross-sectional research linking interleukin-6 (IL-6) and another inflammatory marker, C-reactive protein (CRP), to heart disease and type 2 diabetes-common comorbidities of mental illness-researchers hypothesized a similar association between these markers in childhood and the risk of psychiatric disorders later on. Data from a recent prospective longitudinal study demonstrated they were half right: there was no association with CRP, but higher serum levels of IL-6 in childhood were linked to the development of depression and psychosis in adolescence.

The researchers took blood samples from the 4,500 study subjects-a subset of a general population birth cohort in Avon, England, United Kingdom-to determine both IL-6 and CRP levels when the children were nine years of age and then again when they were 18. Using standardized quantitative measurement tools, researchers assessed the subjects' histories of depression and "psychotic experiences" at age 18 and found a statistically significant association between IL-6 levels and both. The odds ratio (OR) for depression in subjects with the highest IL-6 levels, compared with those with the lowest levels, was 1.55. The ORs for psychotic experiences and a psychotic disorder were 1.81 and 2.4, respectively.

A dose-dependent, linear relationship existed regardless of patient and parent demographics and, maybe more important, independent of a history of childhood psychological or behavioral problems. The relevance of these findings, according to the authors, is that they may help guide the development of new interventions through a better understanding of the role inflammation plays in mental illness, in much the same way it's implicated in other chronic diseases, such as heart disease and diabetes.-Sibyl Shalo Wilmont, BSN, RN

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