To test the hypothesis that higher serum levels of IL-6 and CRP in childhood would increase future risks for depression and psychosis.
MEASUREMENT OF EXPOSURE
Levels of IL-6 and CRP were measured in nonfasting blood samples obtained in participants at age 9 years.
MAIN OUTCOMES AND MEASURES
Participants were assessed at age 18 years. Depression was measured using the Clinical Interview Schedule-Revised (CIS-R) and Mood and Feelings Questionnaire (MFQ), thus allowing internal replication; psychotic experiences (PEs) and psychotic disorder were measured by a semistructured interview.
After adjusting for sex, age, body mass index, ethnicity, social class, past psychological and behavioral problems, and maternal postpartum depression, participants in the top third of IL-6 values compared with the bottom third at age 9 years were more likely to be depressed (CIS-R) at age 18 years (adjusted odds ratio [OR], 1.55; 95% CI, 1.13-2.14). Results using the MFQ were similar. Risks of PEs and of psychotic disorder at age 18 years were also increased with higher IL-6 levels at baseline (adjusted OR, 1.81; 95% CI, 1.01-3.28; and adjusted OR, 2.40; 95% CI, 0.88-6.22, respectively). Higher IL-6 levels in childhood were associated with subsequent risks of depression and PEs in a dose-dependent manner.