Urban–rural environmental exposure during childhood and subsequent risk of inflammatory bowel disease: a meta-analysis

ABSTRACT

Background: The relationship between living conditions in urban and rural areas during childhood and subsequent inflammatory bowel disease (IBD) remains controversial.

Aim: To explore the association between environmental exposures early in life and the subsequent risk of IBD.

Methods: Literature searches were conducted in the following databases: PubMed, EMBASE, and Conference Proceedings Citation Index. Studies were analyzed separately using rate ratios (RRs) or odds ratios (ORs) with 95% confidence intervals.

Results: The search strategy identified 15 studies. Of these, 9 studies explored the association between urban exposure during childhood and ulcerative colitis (UC), and 12 and 4 studies explored this relationship with Crohn’s disease (CD) and IBD, respectively. A meta-analysis showed that the pooled ORs estimated for the case–control studies of UC, CD, and IBD were 1.16 (0.83, 1.61), 1.45 (1.45, 1.85), and 1.34 (1.11, 1.62), respectively. The pooled RR estimated for the cohort studies of CD and IBD was 1.48 (1.17, 1.87). The stratified analysis and meta-regression showed significant relationships between CD and living conditions in case–control studies published during 2010–2017 and in non-European countries (P < 0.05).

Conclusions: Living conditions during childhood are positively associated with the subsequent development of IBD. Urban living environment is more common among those with CD than UC.

KEYWORDS:

• Ulcerative colitis
• Crohn’s disease
• environmental exposure
• childhood
• meta-analysis

Author contributions

C. Song, J. Yang, W. Ye, and Y. Zhang equally contributed to this work. C. Song, J. Yang, W. Ye, and Y. Zhang designed the study, analyzed the data, and wrote the manuscript. C. Song, J. Yang, W. Ye, X. Zhou, and Y. Xie designed the research. C. Song, J. Yang, W. Ye, X. Li, and C. Tang performed the research. Y. Xie designed the study and edited the manuscript as the corresponding author. The authors had full access to the data and take full responsibility for the integrity of the data. All the authors gave their approval for the submission of the final manuscript.

Declaration of interest

The authors have no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript apart from those disclosed.

Reviewer disclosures

Peer reviewers on this manuscript have no relevant financial or other relationships to disclose.

Additional information

Funding

This study was supported by the National Natural Science Foundation of China (No: 81760105) and the Jiangxi Provincial Natural Science Fund (No: 20142BAB205044).