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Nat Rev Gastroenterol Hepatol. 2018 Jan;15(1):39-49. doi: 10.1038/nrgastro.2017.136. Epub 2017 Oct 11.

Environmental triggers in IBD: a review of progress and evidence.

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Massachusetts General Hospital, Harvard Medical School, 165 Cambridge Street, Boston, Massachusetts 02114, USA.
University of Manitoba IBD Clinical and Research Centre, 804-F-175 McDermot Avenue, Winnipeg Manitoba R3E 3P4, Canada.
Center for Systems Biomedicine, Vatche & Tamar Manoukian Division of Digestive Diseases, Department of Medicine, UCLA, 650 Charles E. Young Drive South CHS 44-133, Los Angeles, California 90095-7278, USA.
Gastroenterology/UVCM, Inselspital, Freiburgstrasse 8, 3010 Bern, Switzerland.
I. Department of Medicine, University of Erlangen-N├╝rnberg, University Hospital, Ulmenweg 18, 91054 Erlangen, Germany.
The National University of Malaysia, UKM Medical Centre, Jalan Yaacob Latif, 56000 Kuala Lumpur, Malaysia.
Triemli Hospital, Department of Gastroenterology & Hepatology, Birmensdorferstrasse 497, 8063 Zurich, Switzerland.
Department of Pathobiology, Lerner Research Institute, and Department of Gastroenterology & Hepatology, Digestive Diseases and Surgery Institute, The Cleveland Clinic Foundation, 9500 Euclid Avenue, Cleveland, Ohio 44195, USA.


A number of environmental factors have been associated with the development of IBD. Alteration of the gut microbiota, or dysbiosis, is closely linked to initiation or progression of IBD, but whether dysbiosis is a primary or secondary event is unclear. Nevertheless, early-life events such as birth, breastfeeding and exposure to antibiotics, as well as later childhood events, are considered potential risk factors for IBD. Air pollution, a consequence of the progressive contamination of the environment by countless compounds, is another factor associated with IBD, as particulate matter or other components can alter the host's mucosal defences and trigger immune responses. Hypoxia associated with high altitude is also a factor under investigation as a potential new trigger of IBD flares. A key issue is how to translate environmental factors into mechanisms of IBD, and systems biology is increasingly recognized as a strategic tool to unravel the molecular alterations leading to IBD. Environmental factors add a substantial level of complexity to the understanding of IBD pathogenesis but also promote the fundamental notion that complex diseases such as IBD require complex therapies that go well beyond the current single-agent treatment approach. This Review describes the current conceptualization, evidence, progress and direction surrounding the association of environmental factors with IBD.

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