Abstract and Introduction
Abstract
Background: While the incidence of inflammatory bowel disease (IBD) has stabilised in the West, it is still increasing in several newly industrialised countries.
Aims: To investigate whether the 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.
Results: Overall, 255 studies were assessed. We identified 25 risk factors for IBD, seven of which were noted in both Eastern and Western populations: family history of Crohn's disease [CD] or ulcerative colitis [UC], former smoking (CD/UC), smoking (CD), appendicectomy (CD), tonsillectomy (CD), meat and meat products (CD), and vitamin D deficiency (UC). The remaining factors, including urban living, current smoking, antibiotics, oral contraceptives, caesarean section, isotretinoin, total energy, fat, cholesterol, fatty acids and their sub-classifications, eggs, and soft drinks, were associated with an increased risk of IBD in Western or Eastern populations only. We identified 21 protective factors for IBD, among which eight were common in the East and West: farm animals (CD/UC), Helicobacter pylori infection (CD/UC), multiple births (CD), physical activity (CD), history of breastfeeding (CD), pets (UC), current smoking (UC), and coffee intake (UC). Ten factors conferred protection against IBD in Western populations only, whereas eight factors conferred protection against IBD in Eastern populations only.
Conclusions: Numerous environmental and dietary factors influenced the development of IBD in both Western and Eastern populations, whereas certain factors influenced IBD risk differently in these populations.
Introduction
Inflammatory bowel disease (IBD) is a life-long disease characterised by chronic relapsing and remitting inflammation in the gastrointestinal tract, including Crohn's disease (CD) and ulcerative colitis (UC). While the exact cause of IBD remains unclear, the disease likely develops due to genetic predisposition, environmental and dietary factors, the gut microbiome, and a dysregulated immune response.[1,2]
Epidemiological studies have indicated that although the incidence of IBD is stabilising in Western countries, the disease burden remains high as the prevalence of IBD exceeds 0.3%.[3] Furthermore, the incidence of IBD is increasing significantly in several newly industrialised countries across Asia and South America.[3,4] First-generation immigrants from countries with a low prevalence of IBD who move to high-prevalence countries are at equal or increased risk of IBD compared to the baseline population.[5] An increase in disease incidence among ethnicities and nationalities where IBD was previously uncommon has substantial implications for our understanding of the pathogenesis and environmental triggers of IBD. Moreover, high IBD prevalence is also likely due to the adoption of a Western diet characterised by an increased intake of fat (animal and milk fats, n-6 polyunsaturated fats [PUFAs]) and refined sugars, and low intake of fibre and healthy fats (n-3 PUFAs).[6,7] These data highlight the effects of environmental and dietary changes on the incidence of IBD.
Considering the differences in diet and environment between Western and Eastern countries, it is necessary to identify the environmental triggers of IBD. Although some IBD studies have reported ethnic differences in several etiological factors such as smoking[8] and antibiotic use,[9] their findings were not extensively validated. An umbrella review of meta-analyses reported risk and protective factors related to IBD;[2] however, it did not determine whether these are distinct in different populations. Therefore, the present meta-analysis aimed to explore whether environmental and dietary risk factors for IBD differ between Eastern and Western populations.
Aliment Pharmacol Ther. 2022;55(3):266-276. © 2022 Blackwell Publishing
