Supplementary Material for: Adiponectin Levels in Inflammatory Bowel Disease – A Systematic Review and Meta-analysis

Introduction:
Adipose tissue plays an important role in the pathogenesis of inflammatory conditions. The role of adipokines in inflammatory bowel disease (IBD) has been evaluated in the current literature with conflicting results. The aim of this study was to evaluate adiponectin levels in IBD patients, including Crohn's disease (CD) and ulcerative colitis (UC), compared to controls, as well as further subgroup analyses. Hence, assessing the potential role of adiponectin as a surrogate marker.

Methods:
We performed a systematic electronic search on PubMed, EMBASE, Scopus and Cochrane Library, including observational or interventional studies evaluating serum or plasma adiponectin levels in IBD patients on humans. The primary summary outcome was the mean difference (MD) in serum or plasma adiponectin levels between IBD patients vs. controls. Subgroups analyses were conducted involving adiponectin levels in CD and UC compared to controls, as well as CD compared to UC.

Results:
A total of 20 studies were included in our qualitative synthesis and 14 studies in our quantitative synthesis, with a total population sample of 2,085 subjects. No significant MD in serum adiponectin levels was observed between IBD patients vs. controls (-1.331 [95% CI -3.135–0.472]), UC patients vs. controls (-0.213 [95% CI -1.898–1.472]), and CD patients vs. controls (-0.851 [95% CI -2.263–0.561]). Nevertheless, a significant MD was found between UC patients vs. CD patients (0.859 [95% CI 0.097–1.622]).

Conclusions:
Serum adiponectin levels were not able to differentiate between IBD, UC and CD patients compared to controls. However, significantly higher serum adiponectin levels were observed in UC compared to CD patients.