Background: The inflammatory bowel diseases (IBDs), Crohn's disease (CD) and ulcerative colitis (UC) occur worldwide with differences in epidemiology, etiology and phenotype between regions. Breakthroughs have occurred in IBD genetics, although the genes that predispose to IBD differ between racial groups. What do we know about the ‘envirotype' of those who develop IBD, and are there differences between the East and the West? Key Messages: The strongest IBD risk factor identified to date is a family history of IBD. Whilst likely representing an underlying genetic predisposition, it may also reflect shared environmental factors amongst family members. Cigarette smoking increases the risk of developing CD, whilst smoking is less common in those who develop UC. Having ceased smoking increases the risk of developing UC subsequently. Unlike the West, cigarette smoking appears to play a lesser role in the East. Other environmental risk factors are inconsistent. Studies of migrant populations moving from regions of low to high IBD incidence point to early life as a key time for environmental triggers. In these populations, it is the second generation (those born in the high incidence region) with higher IBD incidence rates than their parents. Early life environmental exposures have been studied exhaustively but, except for having been breastfed, few putative early childhood environmental risk factors have been shown consistently to alter the risk of developing IBD. Conclusions: The identification of IBD environmental risk factors remains elusive in both the East and West. In the West, case-control studies are unlikely to move the field forward without multi-level (phenotype, genotype, diet history, ‘envirotype' and microbiome) data, ideally collected prospectively. Cohort studies (such as the Genes, Environment, Microbiome project) may address some of these issues. However, in the East where IBD incidence is still increasing, well-designed comprehensive case-control studies may identify differences that give an insight into the ‘envirotype' driving IBD incidence.
Early-life environmental risk factors for asthma: findings from the Children's Health Study.
