Gut microbiota composition is known to be important in maintaining health and mediating disease
Dysbiosis, a change in the normal microbial ecology, occurs in the intestine in the context of IBD
Gut inflammation in IBD is characterized by a reduced diversity of microbiota, which could render the host more susceptible to colonization with pathogens or pathobionts
Environmental factors probably have a major role in IBD; antibiotic use, childbirth mode, breastfeeding, air pollution, NSAID use, hypoxia or high altitude, diet and urban environments have been studied
Future studies should adopt a multi-omic big data approach, integrating several layers of data on clinical parameters, environmental exposures, genetics, epigenetics, immunological function and microbial structure
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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A.N.A. has served on advisory boards for AbbVie, Merck and Takeda. C.N.B. is supported in part by the Bingham Chair in Gastroenterology. He has served on advisory Boards for AbbVie Canada, Ferring Canada, Janssen Canada, Napo Pharmaceuticals, Pfizer Canada, Shire Canada and Takeda Canada, and he has acted as a consultant to Mylan Pharmaceuticals. He has received educational grants from AbbVie Canada, Janssen Canada, Shire Canada and Takeda Canada. He has been on the speaker's panel for AbbVie Canada, Ferring Canada and Shire Canada. The other authors declare no competing interests.
Two diseases (Crohn's disease and ulcerative colitis) affecting primarily the digestive tract, characterized by chronic inflammation.
Community of microorganisms comprising bacteria, viruses, fungi, Archaea and eukaryotic microorganisms.
Substances that are foreign to the body.
Microorganisms associated with chronic inflammatory diseases.
A kingdom of single-cell microorganisms without a nucleus or membrane-bound organelles.
A state of reduced oxygenation in the tissues.
The entirety of all environmental exposures of an individual in a lifetime.
DNA methylation and histone modifications that regulate expression of genes within a cell.
Study of chemical fingerprints (metabolites) present within an organism.
Measurement of physical and biochemical traits of an organism.
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Ananthakrishnan, A., Bernstein, C., Iliopoulos, D. et al. Environmental triggers in IBD: a review of progress and evidence. Nat Rev Gastroenterol Hepatol 15, 39–49 (2018). https://doi.org/10.1038/nrgastro.2017.136
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