title: Environmental factors in the relapse and recurrence of inflammatory bowel disease: a review of the literature.
abstract: BACKGROUND
  The causes of relapse in patients with Crohn's disease (CD) and ulcerative colitis (UC) are largely unknown. This paper reviews the epidemiological and clinical data on how medications (non-steroidal anti-inflammatory drugs, estrogens and antibiotics), lifestyle factors (smoking, psychological stress, diet and air pollution) may precipitate clinical relapses and recurrence. Potential biological mechanisms include: increasing thrombotic tendency, imbalances in prostaglandin synthesis, alterations in the composition of gut microbiota, and mucosal damage causing increased permeability.
  
  
  RESULTS
  The clinical epidemiological data consistently reports positive associations between smoking and relapses in CD, and inverse ones with UC. For NSAIDs and estrogens, the epidemiological findings are inconsistent, although general antibiotic use was associated with a reduced risk of relapse in CD. High levels of stress were positively associated with relapse, although psychological interventions did not have therapeutic benefits. The limited work on diet has reported sulphur-containing foods are positively associated with relapse in UC, but there is no work in CD. Ecological data reported positive correlations between air pollution levels and IBD hospitalisations.
  
  
  CONCLUSIONS
  In the future, to clarify this area, more clinical epidemiological work is required where detailed drug types and doses, and complete dietary intakes are measured, in specific forms of IBD. Such work could provide guidance to both patients and doctors to help maintain remission.
authors.affiliation: Norwich Medical School, University of East Anglia, Norwich, NR4 7TJ, UK, Thomas.d.martin@doctors.org.uk.
authors.forename: Thomas D
authors.initials: TD
authors.lastname: Martin
authors.forename: Simon S M
authors.initials: SS
authors.lastname: Chan
authors.forename: Andrew R
authors.initials: AR
authors.lastname: Hart
mesh_terms: D000393:Air Pollutants / Q000009:adverse effects; D000900:Anti-Bacterial Agents / Q000009:adverse effects; D000894:Anti-Inflammatory Agents, Non-Steroidal / Q000009:adverse effects; D003093:Colitis, Ulcerative / Q000175:diagnosis / Q000453:epidemiology* / Q000628:therapy*; D003424:Crohn Disease / Q000175:diagnosis / Q000453:epidemiology* / Q000628:therapy*; D004032:Diet / Q000009:adverse effects; D004777:Environment; D004781:Environmental Exposure / Q000009:adverse effects; D004967:Estrogens / Q000009:adverse effects; D006801:Humans; D012008:Recurrence; D018570:Risk Assessment; D012307:Risk Factors; D012907:Smoking / Q000009:adverse effects / Q000453:epidemiology; D013315:Stress, Psychological / Q000453:epidemiology; D016896:Treatment Outcome
chemical_list: D000393:Air Pollutants; D000900:Anti-Bacterial Agents; D000894:Anti-Inflammatory Agents, Non-Steroidal; D004967:Estrogens