A Mendelian randomization study of daytime napping and inflammatory bowel disease

Background Recently, the potential effects of daytime napping on inflammatory bowel disease has aroused great interest in research community. However, the causal relationship between daytime napping and inflammatory bowel disease remains uncertain. Methods A series of quality control steps were conducted to extract the eligible single nucleotide polymorphisms for the two-sample MR analysis. Next, we performed the Inverse Variance Weighted as the primary method to estimate causal effects, with the Weighted Median and Maximum Likelihood as the supplementary method. Furthermore, the Cochran's Q test, Egger intercept, MR-PRESSO and Leave-one-out method for sensitivity analyses. Results The initial MR analysis demonstrated that the daytime napping causally reduced the risk of inflammatory bowel disease ( OR  = 0.327, P  = 0.006) and ulcerative colitis ( OR  = 0.300, P  = 0.017), but the association was not found in the daytime napping and Crohn's disease ( OR  = 0.520, P  = 0.445). Additionally, consistent with the initial results, the replication analysis result showed that the daytime napping was a protective factor for UC ( OR  = 0.988, P  = 0.007), but no relation with inflammatory bowel disease ( OR  = 1.006, P  = 0.212). No significant evidence of heterogeneity and horizontal pleiotropy were identified by sensitivity analyses. Conclusion Our MR study supported the causal effect of daytime napping on ulcerative colitis, as well as into the prevention of ulcerative colitis pathogenesis through targeting sleep habit.