Association between metabolic syndrome and inflammatory bowel disease: a bidirectional two-sample Mendelian randomized study

Introduction Epidemiological studies have revealed parallel increases in the incidences of metabolic syndrome (MetS) and inflammatory bowel disease (IBD). Clinical observational studies have shown a link between MetS and a poor prognosis of IBD. However, the causal relationship between MetS and IBD remains unclear. This study used bidirectional two-sample Mendelian randomisation to investigate potential causal links between MetS and IBD, including ulcerative colitis (UC) and Crohn’s disease (CD). Material and methods Genetic associations of MetS and components, IBD were sourced from public databases of European populations. Inverse variance weighting was conducted, with weighted median, Mendelian randomisation–Egger, and Mendelian randomization (MR) Pleiotropy Residual Sum and Outlier methods used as sensitivity analyses. This process was repeated in the opposite direction. Results The Inverse variance weighted (IVW) method showed that genetic prediction of MetS may be a potential risk factor for CD (OR=1.34, 95% CI: 1.009–1.779; P=0.043). In further estimating the different components of MetS, waist circumference may increase the risk of CD (OR=1.33, 95% CI: 1.05–1.684; P=0.018) and hypertension may increase the risk of UC (OR=1.61, 95% CI: 1.084–2.39; P=0.018). In reverse analysis, IBD may increased triglyceride levels (OR=1.019, 95% CI: 1.000–1.038; P=0.049). Conclusions This MR Analysis showed a causal relationship between genetically predicted MetS and CD, and genetically predicted hypertension and UC. Therefore, these patients need to be closely monitored clinically for the risk of CD/UC comorbidities. In patients with IBD, close monitoring of MetS-associated cardiovascular risk is required.