A comprehensive updated cross-sectional and longitudinal meta-analysis of cytokines in eating disorders

Background Prior research has found altered levels of immune signalling proteins, such as cytokines, in people with eating disorders (EDs). This study is an update of a previously published meta-analysis. Methods This systematic review and meta-analysis assessed cross-sectional and longitudinal studies from four databases (PubMed, Web of Science, MEDLINE and PsycINFO) reporting cytokine concentrations in people with EDs. Random-effects models were utilised for all meta-analyses. Results Twenty-four new studies were incorporated, resulting in a total of 43 studies included in the meta-analyses. Interleukin (IL)-6 and IL-15 were higher, and IL-7 was lower, in AN compared with HC. When controlling for outliers, concentrations of tumour necrosis factor (TNF)-α, IL-1β, IL-4, IL-8, IL-10, IFN-γ, monocyte chemoattractant protein (MCP) and transforming growth factor (TGF)-β were similar between AN and HC. Longitudinally, IL-6 was lower in AN at follow-up compared to baseline, whereas TNF-α and IL-1β did not change. There were largely no differences in IL-6 and TNF-α in BN and were insufficient studies to perform meta-analyses for binge eating disorder (BED) or other EDs. Conclusion In acute AN, concentrations of IL-6 and IL-15 are elevated and IL-7 is decreased, with evidence for normalisation of IL-6 over the course of weight restoration. Concentrations of other cytokines considered to broadly have pro-inflammatory functions were not increased in AN. In people with BN, there is less evidence for increases in pro-inflammatory cytokines, but the evidence base is limited. Methodological considerations for future studies are recommended.