The first step of the mediation MR showed that IBD was associated with increased butyrate levels, decreased serotonin levels, increased C-reactive protein (CRP), increased interleukin-6 (IL-6), increased percentage of neutrophils, decreased percentage of lymphocytes, and decreased total body bone mineral density, but the second step of the analysis revealed no significant evidence that the above factors were mediators of the causal effects of IBD on AS, PsA, and ReA. Here, IL6 is linked to inflammatory bowel disease.