By Eleanor McDermid, Senior medwireNews Reporter
Elevated levels of the inflammatory marker interleukin (IL)-6 in childhood are associated with an increased risk of psychosis and depression in adulthood, research shows.
“Inflammation might explain the high comorbidity between these neuropsychiatric disorders and chronic physical illness, such as heart disease and diabetes mellitusâ€, observe the researchers, led by Golam Khandaker (University of Cambridge, UK).
The team used data from the Avon Longitudinal Study of Parents and Children. Of the more than 14,000 participants, 5076 had blood samples taken at the age of 9 years that were sufficient for the measurement of IL-6 and C-reactive protein (CRP). From these, the researchers excluded 491 children with recent infection at the time of the blood draw.
Only 2528 of the participants with inflammatory marker data attended assessment for psychotic experiences at age 18 years, and 2453 were assessed for depression. Khandaker et al note that, compared with participants who were assessed, those who did not attend more often had factors associated with psychiatric outcomes at age 18, namely, psychological problems in childhood, low socioeconomic status and mothers with high postpartum depression scores.
“Thus, it is likely that any bias from sample attrition has led to an underestimation of the true association between IL-6 and later psychiatric morbidityâ€, they write in JAMA Psychiatry.
At the age of 18, 4.0% of participants reported psychotic experiences, 1.4% met the criteria for a psychotic disorder and 17.2% met the criteria for depression. After accounting for potential confounders, IL-6 levels were significantly associated with psychiatric outcomes, whereas CRP levels were not.
Participants in the top versus the bottom third of childhood IL-6 levels were a significant 1.81-fold more likely to report psychotic experiences at age 18, and a nonsignificant 2.40-fold more likely to meet the stricter definition of a psychotic disorder. They were also a significant 1.55-fold more likely to have depression.
There was a linear relationship between IL-6 levels and both psychotic and depressive outcomes, with each standard deviation increase being associated with 24% and 14% increases in the risk of psychotic experiences and depression, respectively.
The researchers note that early trials of adjuvant anti-inflammatory treatment in psychiatric disorders has met with “encouraging resultsâ€, but cite the need for more targeted interventions.
“A clearer understanding of the role of inflammation in the pathogenesis of depression and psychosis may lead to new treatmentsâ€, they conclude.
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