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Epidemiology and risk factors for IBD

Key Points

  • Crohn's disease and ulcerative colitis are complex immunologically mediated diseases that arise due to a dysregulated immune response to commensal flora in a genetically susceptible host

  • The incidence of IBD has traditionally been highest in North America and Western Europe with many cohorts suggesting a substantial secular increase over the second half of the twentieth century

  • However, incidence of IBD is increasing in emerging populations such as Asia, suggesting that changing environmental factors play an important part

  • Smoking and appendectomy were initially described to increase the risk of Crohn's disease and confer protection from ulcerative colitis; however, this relationship seems more complex and could be mediated by genetics

  • Diet, lifestyle and behaviour, as well as perturbations of the gut microbiota through use of antibiotics, might also have important roles in disease pathogenesis

  • Modification of IBD risk factors offer avenues of intervention for disease prevention and improvement of natural history

Abstract

IBD, comprising Crohn's disease and ulcerative colitis, is a chronic immunologically mediated disease at the intersection of complex interactions between genetics, environment and gut microbiota. Established high-prevalence populations of IBD in North America and Europe experienced the steepest increase in incidence towards the second half of the twentieth century. Furthermore, populations previously considered 'low risk' (such as in Japan and India) are witnessing an increase in incidence. Potentially relevant environmental influences span the spectrum of life from mode of childbirth and early-life exposures (including breastfeeding and antibiotic exposure in infancy) to exposures later on in adulthood (including smoking, major life stressors, diet and lifestyle). Data support an association between smoking and Crohn's disease whereas smoking cessation, but not current smoking, is associated with an increased risk of ulcerative colitis. Dietary fibre (particularly fruits and vegetables), saturated fats, depression and impaired sleep, and low vitamin D levels have all been associated with incident IBD. Interventional studies assessing the effects of modifying these risk factors on natural history and patient outcomes are an important unmet need. In this Review, the changing epidemiology of IBD, mechanisms behind various environmental associations and interventional studies to modify risk factors and disease course are discussed.

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Figure 1: The interaction between genetics, immunology, environment and microbiome.
Figure 2: Global map of IBD in established and emerging populations.

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Acknowledgements

A.N.A. is supported by funding from the US National Institutes of Health (K23 DK097142).

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Correspondence to Ashwin N. Ananthakrishnan.

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A.N.A. has served on the scientific advisory boards for Abbvie and Cubist pharmaceuticals.

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Ananthakrishnan, A. Epidemiology and risk factors for IBD. Nat Rev Gastroenterol Hepatol 12, 205–217 (2015). https://doi.org/10.1038/nrgastro.2015.34

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