Causal relationship between asthma and inflammatory bowel disease : A two-sample bidirectional mendelian randomization analysis.

• We found a correlation between asthma and Crohn's disease, whereas there seems to be no association with ulcerative colitis. However, this result is not yet robust and further research is needed. • The present study seems to further confirm the existence of gut-lung axis. • Clinicians should be aware of possible links between asthma and gut and assess for comorbidities. : Based on the findings of current observational studies, asthma and inflammatory bowel disease (including Crohn's disease and ulcerative colitis) are associated; however, their causal association cannot be established due to methodological limitations. : we use two-sample bidirectional mendelian randomization (MR) to overcome the confounding factors and explore the causal link between asthma and inflammatory bowel disease. : After selecting asthma and IBD-related genome-wide association studies (GWAS) data and screening single nucleotide polymorphisms (SNPs), MR analysis was performed by four methods: inverse variance weighted (IVW), MR-Egger, maximum likelihood, and weighted median (WM), while Cochran's Q test was used to detect heterogeneity and MR-Egger intercept to detect horizontal pleiotropy. Finally, we used the leave-one-out method and funnel plot to perform sensitivity analysis. : We screened 57, 59, and 60 SNPs in the association analysis of asthma and IBD, CD, and UC, respectively. The results of MR analysis showed that asthma only increased the risk of CD (IVW: OR = 1.1712, 95% CI = 1.0418-1.3167, P value = 0.0082; maximum likelihood: OR = 1.1739, 95% CI = 1.0428-1.3215, P value = 0.0080). Neither forward nor reverse MR analysis revealed heterogeneity or horizontal pleiotropy. Similarly, we did not find potential directional pleiotropy by funnel plot, and the leave-one-out method did not suggest a significant effect of a single SNP on the overall results. : we found a negative correlation between asthma and Crohn's disease, but more research is needed to confirm this. [ABSTRACT FROM AUTHOR]