A Meta-Analysis of Environmental and Dietary Risk Factors for Inflammatory Bowel Disease: A Comparison Between Eastern and Western Populations

Background: The incidence of inflammatory bowel disease (IBD) is still increasing in many newly industrialized countries. We mainly investigated whether environmental and dietary risk factors for IBD differ between Eastern and Western populations. Methods: We systematically searched PubMed, Embase, and Web of Science for studies published from inception through June 30, 2020. Data were pooled using a random effects model. Findings: 237 studies were included. A total of 26 risk factors for IBD were identified, six of which were consistent in both Eastern and Western populations: appendectomy (Crohn’s disease (CD)), tonsillectomy (CD), family history of IBD (CD/ulcerative colitis (UC)), urban living (CD), former smoking (UC), and fat intake (UC). Ten factors were associated with an increased risk of IBD in Western and Eastern populations only. We also identified 23 protective factors for IBD, among which eight were consistent in the East and West: contact with farm animals (CD/UC), having ≥2 siblings (CD), physical activity (CD/UC), Helicobacter pylori infection (CD/UC), contact with pets (UC), current smoking (UC), fruit intake (UC), and coffee intake (UC). Eight factors conferred protection against IBD in Western populations only, whereas seven factors conferred protection against IBD in Eastern populations only. Interpretation: Numerous environmental and dietary factors consistently influence the development of IBD in Western and Eastern populations. However, some factors influence IBD risk differently in these populations. Funding Statement: Supported by National Natural Science Foundation of China (NSFC grant No. 81630018, No. 81870384). The Leona M. & Harry B. Helmsley Charitable Trust Grant (grant No. 2019PG-CD018). Declaration of Interests: All authors declare no competing interests.