Epidemiological and translational data increasingly implicate environmental pollutants in inflammatory bowel disease (IBD). Indeed, the global incidence of IBD has been rising, particularly in developing countries, in parallel with the increased use of chemicals and synthetic materials in daily life and escalating pollution levels. Recent nationwide and ecological studies have reported associations between agricultural pesticides and IBD, particularly Crohn’s disease. Exposure to other chemical categories has also been linked with an increased risk of IBD. To synthesise available data and identify knowledge gaps, we conducted a systematic review of human studies that reported on the impact of environmental pollutants on IBD risk and outcomes. Furthermore, we summarised in vitro data and animal studies investigating mechanisms underlying these associations. The 32 included human studies corroborate that heavy and transition metals, except zinc, air pollutants, per- and polyfluorinated substances, and pesticides are associated with an increased risk of IBD, with exposure to air pollutants being associated with disease-related adverse outcomes as well. The narrative review of preclinical studies suggests several overlapping mechanisms underlying these associations, including increased intestinal permeability, systemic inflammation and dysbiosis. A consolidated understanding of the impact of environmental exposures on IBD risk and outcomes is key to the identification of potentially modifiable risk factors and to inform strategies towards prediction, prevention and mitigation of IBD.

Summary: Background: Phase III trials have demonstrated the efficacy and safety of ustekinumab in moderate‐to‐severe ulcerative colitis (UC), but few real‐world data are currently available.Aim: To assess short‐term effectiveness and safety of ustekinumab in patients with UC.Methods: From January to September 2019, all patients with UC treated with ustekinumab in 20 French GETAID centres were retrospectively included. The primary outcome was steroid‐free clinical remission (partial Mayo Clinic score ≤2) at weeks 12‐16 without a rectal bleeding subscore >1.Results: Among the 103 patients included, 70% had been previously exposed to ≥2 anti‐TNF agents and 85% to vedolizumab. At weeks 12‐16, steroid‐free clinical remission and clinical remission rates were 35.0% and 39.8% respectively; the absence of rectal bleeding with normal stool frequency was noted in 19.4% of patients. Two patients discontinued ustekinumab before the week 12‐16 visit and underwent surgery. In multivariable analysis, a partial Mayo Clinic score >6 at inclusion (18.6% vs 46.7%, P = 0.003) and a history of both exposure to anti‐TNF and vedolizumab therapies (27.3% vs 80.0%, P = 0.001) were negatively associated with steroid‐free clinical remission at weeks 12‐16. Adverse events occurred in 7.8% of patients and serious adverse events in 3.9% of patients.Conclusion: In a cohort of highly refractory patients with UC with multiple prior drug failures, ustekinumab provided steroid‐free clinical remission in one‐third of cases at weeks 12‐16. Clinical severity and previous use of anti‐TNF and vedolizumab therapies were associated with ustekinumab failure at weeks 12‐16.