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Geographical variability and environmental risk factors in inflammatory bowel disease
  1. Siew C Ng1,
  2. Charles N Bernstein2,
  3. Morten H Vatn3,
  4. Peter Laszlo Lakatos4,
  5. Edward V Loftus Jr5,
  6. Curt Tysk6,
  7. Colm O'Morain7,
  8. Bjorn Moum8,
  9. Jean-Frédéric Colombel9,
  10. on behalf of the Epidemiology and Natural History Task Force of the International Organization of Inflammatory Bowel Disease (IOIBD)
  1. 1Department of Medicine and Therapeutics, Institute of Digestive Disease, Li Ka Shing Institute of Health Sciences, Chinese University of Hong Kong, Hong Kong, Hong Kong
  2. 2Department of Internal Medicine, University of Manitoba IBD Clinical and Research Centre, Winnipeg, Manitoba, Canada
  3. 3Department of Gastroenterology, University of Oslo, Institute of Clinical Medicine, EpiGen, Campus AhusOslo University Hospital, Oslo, Norway
  4. 41st Department of Medicine, Semmelweis University, Budapest, Hungary
  5. 5Division of Gastroenterology and Hepatology, Mayo Clinic, Rochester, Minnesota, USA
  6. 6Department of Gastroenterology, Orebro University Hospital and School of Health and Medical Sciences, Orebro University, Orebro, Sweden
  7. 7Department of Gastroenterology, Adelaide and Meath Hospital, Trinity College Dublin, Dublin, Leinster, Ireland
  8. 8Department of Gastroenterology, Oslo University Hospital and University of Oslo, Institute of Clinical Medicine, Oslo, Norway
  9. 9Division of Gastroenterology, Mount Sinai School of Medicine, New York, New York, USA
  1. Correspondence to Dr Siew C Ng, Department of Medicine and Therapeutics, Institute of Digestive Disease, Li Ka Shing Institute of Health Sciences, Prince of Wales Hospital, Chinese University of Hong Kong, Shatin, NT, Hong Kong, Hong Kong; siewchienng{at}


The changing epidemiology of inflammatory bowel disease (IBD) across time and geography suggests that environmental factors play a major role in modifying disease expression. Disease emergence in developing nations suggests that epidemiological evolution is related to westernisation of lifestyle and industrialisation. The strongest environmental associations identified are cigarette smoking and appendectomy, although neither alone explains the variation in incidence of IBD worldwide. Urbanisation of societies, associated with changes in diet, antibiotic use, hygiene status, microbial exposures and pollution have been implicated as potential environmental risk factors for IBD. Changes in socioeconomic status might occur differently in different geographical areas and populations and, consequently, it is important to consider the heterogeneity of risk factors applicable to the individual patient. Environmental risk factors of individual, familial, community-based, country-based and regionally based origin may all contribute to the pathogenesis of IBD. The geographical variation of IBD provides clues for researchers to investigate possible environmental aetiological factors. The present review aims to provide an update of the literature exploring geographical variability in IBD and to explore the environmental risk factors that may account for this variability.

  • Inflammatory Bowel Disease
  • Epidemiology
  • Ulcerative Colitis
  • Crohn's Disease

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