Review article: changes in the epidemiology of inflammatory bowel disease-clues for aetiology

Background: The changing epidemiology of inflammatory bowel disease (IBD) in both the developed and developing worlds may provide insights into disease aetiology. Factors that impact on the gut microbiome are leading aetiological candidates. Aim: To review epidemiological studies and trends that identify risk factors for the development of IBD. Methods: Studies that identified factors associated with the development of IBD differentially in children and adults were reviewed. There was a focus on epidemiological studies and on studies that involve the gut microbiome. Results: Use of antibiotics has been shown to be associated with development of Crohn's disease in childhood (odds ratio, OR = 2.75, 95% CI 1.72-4.38). Breastfeeding has been protective against developing IBD (OR=0.69, 95% CI 0.51-0.94), but there is a paucity of data exploring duration of breastfeeding and timing of introduction of bottled milk or table food. Antibiotics and diet changes can also impact on adults enhancing the risk for IBD. Both smoking (OR=1.76, 95% CI 1.40-2.22) and oral contraceptives (relative risk=1.46, 95% CI 1.26-1.70) increase the risk for Crohn's disease and their use is associated with worse outcomes in Crohn's disease. It is unclear if their impact is mediated through the gut microbiome. Conclusions: A leading aetiological clue for IBD based on epidemiological studies is the antecedent use of antibiotics both for children and adults. Some dietary changes may be a risk for adults but there is a paucity of dietary data in children prior to IBD development. Both antibiotic use and dietary changes have the potential to impact the gut microbiome, which in turn can alter the gut immune response.