Early life adversity exposure and circulating markers of inflammation in children and adolescents: A systematic review and meta-analysis

•The aggregated effect size of early adversity on CRP is very small, z = .07.•The aggregated effect size of early adversity on IL-6 is very small, z = .17.•More studies looking at TNF-α are needed.•More studies using in vitro assays of immune cells are needed. This study provides a comprehensive review of the published research on the association between early life adversity and markers of inflammation in children and adolescents. We conducted a systematic review of the published literature on the association between early life adversity and markers of inflammation in pediatric populations. To date, 27 studies have been published in this area representing a wide range of global populations and diverse methods of which nearly half were prospective, longitudinal studies. Of these 27, only 12 studies shared an inflammatory outcome with 4 or more other studies; 9 for CRP, and 6 for IL-6. The association between early life adversity and both CRP, z = .07 [.04, .10], and IL-6, z = .17 [−.07, .42], were small and only significant for CRP although comparable in magnitude to the effects observed in adult samples. Descriptively, the association between early life adversity and CRP appeared to be stronger in studies conducted in infants and adolescents compared with middle childhood. There was minimal evidence of publication bias for studies measuring CRP, but evidence of publication bias for studies using IL-6. Eight studies have looked at the association between early life adversity and stimulated inflammatory cytokines in vitro, and both the methods and results of these studies were mixed; the majority observed exaggerated production of inflammatory cytokines despite mixed methodological approaches that make comparisons across studies difficult. In summary, the evidence supporting an association between early life adversity and inflammation in pediatric samples is limited so far by the number of studies and their heterogeneous methodological approaches. More research that is grounded in a developmental framework and informed by the complexity of the innate immune system is needed in this area.