D Piovani et al. Gastroenterol 2019; 157: 647-59. This study examined environmental risk factors for inflammatory bowel disease after extensive literature review and assessment of meta-analysis.
9 factors that were associated with increased risk of IBD:
- smoking (CD)
- urban living (CD & IBD)
- appendectomy (CD)
- tonsillectomy (CD)
- antibiotic exposure (IBD)
- oral contraceptive use (IBD)
- consumption of soft drinks (UC)
- vitamin D deficiency (IBD)
- Heliobacter species (non-Helicobacter pylori-like) (IBD)
7 factors that associated with reduced risk of IBD:
- physical activity (CD)
- breatfeeding (IBD)
- bed sharing (CD)
- tea consumption (UC)
- high folate levels (IBD)
- high vitamin D levels (CD)
- H pylori infection (CD, UC, and IBD)
EL Barnes et al. Inflamm Bowel Dis 2019; 1474-80. In this review which identified 12 studies and 4843 with an IPAA ( ileal pouch-anal anastomosis) for ulcerative colitis, 10.3% were ultimately diagnosed with Crohn’s disease. Link to full text and video explanation: The Incidence and Definition of Crohn’s Disease of the Pouch: A Systematic Review and Meta-analysis
EV Loftus et al. Inflamm Bowel Dis 2019; 1522-31. In this study with 2057 adalimumab-naive patients, “the proportion of patients in HBI remission increased from 29% (573 of 1969; baseline) to 68% (900 of 1331; year 1) and 75% (625 of 831; year 6). Patients stratified by baseline immunomodulator use had similar HBI remission rates.” Full text: Adalimumab Effectiveness Up to Six Years in Adalimumab-naïve Patients with Crohn’s Disease: Results of the PYRAMID Registry
The following study was summarized in previous blog: Oral Antibiotics For Refractory Inflammatory Bowel Disease Full text link: Efficacy of Combination Antibiotic Therapy for Refractory Pediatric Inflammatory Bowel Disease
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I had not heard of the term “exposome” until last week (Gastroenterology 2012; 142: 1403-4). However, this term was coined in 2005 (Cancer Epidemiol Biomarkers Prev 2005; 14: 1847-50). This term is meant to describe the environmental analog of the genome.
Particularly with the gastrointestinal tract, environmental exposures are often considered a cofactor in disease development. While there has been an increased understanding of the role of genes in the development of disease, it is abundantly clear that environment exposures can independently cause disease or act as a ‘second hit.’ The gastrointestinal tract is exposed to fluids which contain a multitude of elements and microorganisms, and to foods with their variability in nutrients, microbes and pollutants. Other environmental factors include smoking, ionizing radiation, noise, breastfeeding, medications, and antimicrobials.
This cited commentary explains how environmental scientists are trying to unravel the ‘exposome.’
- Bottom-up strategy: measure external sources of the individual exposome at multiple time points. This strategy may benefit from improvement in informatics, remote & personal sensing devices.
- Top-down strategy: examines internal milieu including blood, biologic specimens, and transcriptomics/proteonomics. Early examples include distinct signatures associated with specific environmental exposures.
Both strategies require validation to understand how external exposures trigger internal changes and disease expression. Promising fields in gastroenterology for the study of the exposome include IBD, gastrointestinal cancers, functional disorders, and even obesity. It is likely that studies of the exposome will answer questions about why the frequency of so many diseases are changing much more readily than studies of the genome.
Related blog posts:
Eat your veggies…if you don’t want to get sick
Why are we seeing so many more cases
- -PLoS One 2010; 5 e10746. Novel associations between type 2 diabetes and specific chemical exposures.
- -Nature 2006; 444: 1027-31. Obesity-associated gut microbiome.
- -BMC Med Genomics 2010; 3: 17. Chemical factors associated with disease-related gene expression data.