Elevated IL-6 in childhood linked with later depression, psychotic experiences

By Will Boggs MD

NEW YORK (Reuters Health) - Children with elevated interleukin-6 (IL-6) levels at age nine have an increased risk of developing depression and psychotic experiences when they reach 18, according to a new study.

"Inflammation may be a common mechanism for depression, psychosis, heart disease, and diabetes mellitus -- all of these conditions are associated with higher levels of inflammatory markers such as IL-6," Dr. Golam M. Khandaker from the University of Cambridge in the UK told Reuters Health by email.

"Therefore, reducing low grade systemic inflammation by healthy diet and exercise would reduce the risks of a number of chronic illnesses," he suggested.

Several markers of inflammation, including IL-6 and C-reactive protein (CRP), have been associated with depression, psychosis, and psychotic relapse in cross-sectional studies. There have been few longitudinal studies of these links.

Dr. Khandaker and colleagues used data from the Avon Longitudinal Study of Parents and Children (ALSPAC) to investigate the possible association between serum IL-6 and CRP levels in childhood and the risks for depression and psychosis at age 18 years.

Serum IL-6 levels in the top tertile were associated with a significant 55% increase in depression risk compared with the bottom tertile, the team reports in JAMA Psychiatry, online August 13.

High levels of IL-6 were also tied to a significantly higher risk of having psychotic experiences (adjusted odds ratio, 1.81) and an insignificant increase in the risk of of psychotic disorder.

Each standard deviation increase in IL-6 was associated with a 14% increase in the risk of depression and a 24% increase in the risk of psychotic experiences.

The association between IL-6 and later psychiatric outcomes appeared to be independent of the effect of early-life psychological and behavioral problems on IL-6 levels, and there were no sex differences in the associations between IL-6 and subsequent psychiatric outcomes.

The researchers found no association between CRP levels and psychiatric outcomes.

"Inflammatory pathways may provide important new prevention and intervention targets for major mental illnesses while also undermining the unhelpfully persistent Cartesian division between the mind and body," they conclude.

"If inflammation play a causal role in some cases of depression, anti-inflammatory drugs may be helpful for these patients alongside antidepressants," Dr. Khandaker suggested. "There is already some data from randomized controlled trials to support this view. However, we need more research before advocating anti-inflammatory drugs for treatment of depression in routine practice."

"Measuring IL-6 for the prediction of future depression will be unhelpful because IL-6 levels can be influenced by a number of factors," Dr. Khandaker cautioned. "Besides, depression is a multifactorial condition -- no one risk factor is necessary or sufficient to cause the illness. However, the results from the study point towards to an inflammatory mechanism for depression."

SOURCE: http://bit.ly/1tiqNpe

JAMA Psychiatry 2014.

(c) Copyright Thomson Reuters 2014. Click For Restrictions - http://about.reuters.com/fulllegal.asp