Assessing the impact of blood pressure in the development of inflammatory bowel disease

The purpose of this study is to investigate the potential causal relationships between blood pressure and inflammatory bowel disease (IBD) by using the bidirectional Mendelian randomization (MR) approach. Summary-level data for blood pressure was extracted from the hitherto largest genome-wide study (GWAS) with 759 601 participants of European-descent. We used 56 single nucleotide polymorphisms (SNPs) as instrumental variables (IVs) for blood pressure. Summary statistics for IBD were derived from a GWAS with an overall 59 957 participants of European ancestry, of which 109 IVs were selected. Several robust analytical methods, including inverse-variance weighted (IVW) method, weighted-median method, MR-Egger regression, MR-PRESSO test, maximum likelihood method, "leave-one-out" and multivariable MR analysis were used to evaluate the causal associations between blood pressure and IBD. Genetically predicted higher systolic blood pressure (SBP) was associated with an increased risk of IBD (odds ratio (OR) = 1.05, 95% confidence interval (CI):1.02-1.08, P = .001 by IVW). Subgroup analysis showed that higher SBP was positively associated with Crohn's disease (CD) (OR = 1.06, 95% CI:1.03-1.09, P = 9.18 × 10^-5 ) and ulcerative colitis (UC) (OR = 1.05, 95% CI:1.01-1.09, P = .017) risk, respectively. In reverse-direction MR analysis, the authors observed no evidence for the causal effect of IBD on blood pressure. Our findings suggested that high SBP was associated with an increased risk of IBD (for both UC and CD). Further studies are required to clarify the underlying mechanism of this causal association.