Does type 1 diabetes serve as a protective factor against inflammatory bowel disease: A Mendelian randomization study.

Background: The impact of type 1 diabetes (T1D) on inflammatory bowel disease (IBD) remains unclear.

Objective: To analyze the causal relationship between T1D and IBD using Mendelian ran-domization (MR).

Methods: Single nucleotide polymorphisms were sourced from FinnGen for T1D, IBD, ulcerative colitis (UC) and Crohn's disease (CD). Inverse variance-weighted, MR-Egger, and weighted median tests were used to assess exposure-outcome causality. The MR-Egger intercept was used to assess horizontal pleiotropy. Co-chran's Q and leave-one-out method were used to analyze heterogeneity and sensitivity, respectively.

Results: Our MR analysis indicated that T1D was associated with a reduced risk of IBD [odds ratio (OR): 0.959; 95% confidence interval (CI): 0.938-0.980; P < 0.001] and UC (OR: 0.960; 95%CI: 0.929-0.992; P = 0.015), with no significant association observed in terms of CD risk (OR: 0.966; 95%CI: 0.913-1.022; P = 0.227). The MR-Egger intercept showed no horizontal pleiotropy (P > 0.05). Cochran's Q and leave-one-out sensitivity analyses showed that the results were not heterogeneous (P > 0.05) and were robust.

Conclusions: This MR analysis suggests that T1D serves as a potential protective factor against IBD and UC but is independent of CD.