Supplementary Material for: Does atopic dermatitis increase the risk of inflammatory bowel disease? A meta-analysis of data from 61 million participants

Background: This review aimed to examine if atopic dermatitis (AD) led to an increased risk of inflammatory bowel disease (IBD) by collating data from longitudinal studies. Summary: Cohort and case-control studies examining the risk of IBD, Crohn’s disease (CD), or ulcerative colitis (UC) due to exposure to AD were included in this review. Articles were searched on PubMed, CENTRAL, Embase, Scopus, and Web of Science electronic repositories up to 2nd October 2024. Eight retrospective cohort studies with 61,190,816 participants were included. The meta-analysis found that AD was a significant risk factor for IBD (OR: 1.37 95% CI: 1.31, 1.43). No statistical heterogeneity was noted. Pooled analysis showed that exposure to AD was a significant risk factor for both CD (OR: 1.51 95% CI: 1.31, 1.76) and UC (OR: 1.33 95% CI: 1.13, 1.56). Both meta-analyses had high inter-study heterogeneity with I2=83% and I2=89% respectively. Results remained significant on sensitivity analysis. Key Messages: Our study shows an association between AD and IBD. The association was persistent for both CD and UC. Given the small increase in risk of IBD in AD, its clinical relevance may be questionable.