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Meta-Analysis
. 2016 Sep;22(9):2191-9.
doi: 10.1097/MIB.0000000000000852.

Environmental Hygiene and Risk of Inflammatory Bowel Diseases: A Systematic Review and Meta-analysis

Aurada Cholapranee  1 , Ashwin N Ananthakrishnan
Affiliations
Meta-Analysis

Environmental Hygiene and Risk of Inflammatory Bowel Diseases: A Systematic Review and Meta-analysis

Aurada Cholapranee et al. Inflamm Bowel Dis. 2016 Sep.

Abstract

Background: According to the hygiene hypothesis, individuals raised in a sanitary environment have a higher risk of developing inflammatory bowel diseases (IBD). However, results have been inconsistent. We conducted this systematic review of factors related to environmental hygiene and risk of IBD, Crohn's disease (CD) and ulcerative colitis (UC).

Methods: A systematic search was performed on MEDLINE between 1980 and 2015 to identify studies of the association between IBD and contact with pets and farm animals, number of siblings, bedroom sharing in childhood, and access to personal toilet and hot water. Random- or fixed-effect meta-analyses were performed, and analysis further stratified based on ethnicity of the included cohort.

Results: A total of 29 relevant studies were included. Having a pet (odds ratio [OR], 0.76; 95% confidence interval [CI], 0.63-0.88) and contact with farm animals was inversely associated with risk of IBD (OR, 0.45; 95% CI, 0.31-0.60). However, the strength of association with farm animals was statistically stronger in non-white cohorts (OR, 0.27; 95% CI, 0.02-0.53) than in white cohorts (OR, 0.55; 95% CI, 0.45-0.65) (P = 0.028). Access to toilet (OR, 0.71; 95% CI, 0.56-0.85) and hot water (OR, 0.67; 95% CI, 0.44-0.89) was inversely associated with UC in non-white populations but not whites. Having more than 2 siblings was inversely associated with risk of CD.

Conclusions: Several factors pertaining to reduced environmental hygiene are inversely associated with risk of IBD. However, underlying ethnicity influences susceptibility to the effect of these factors.

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Conflict of interest statement

Cholapranee has no conflicts of interest to declare.

Figures

Figure 1
Figure 1. Flowchart of search strategies to identify relevant studies investigating association between measures of environmental hygiene and risk of inflammatory bowel diseases
Figure 2
Figure 2. Association between exposure to pets and risk of Crohn's disease and ulcerative colitis
(a) Crohn's disease (b) Ulcerative colitis
Figure 2
Figure 2. Association between exposure to pets and risk of Crohn's disease and ulcerative colitis
(a) Crohn's disease (b) Ulcerative colitis
Figure 3
Figure 3. Effect of ethnicity on association between exposure to farm animals and risk of inflammatory bowel diseases
(a) Whites (b) Non-whites
Figure 3
Figure 3. Effect of ethnicity on association between exposure to farm animals and risk of inflammatory bowel diseases
(a) Whites (b) Non-whites
Figure 4
Figure 4. Effect of ethnicity on association between access to toilets and risk of ulcerative colitis
(a) Whites (b) Non-whites
Figure 4
Figure 4. Effect of ethnicity on association between access to toilets and risk of ulcerative colitis
(a) Whites (b) Non-whites
See this image and copyright information in PMC

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