Effects of environmental contaminants in inflammatory bowel disease: a systematic review

Abstract

Introduction: The Inflammatory Bowel Disease (IBD) is characterized by a chronic inflammation of the gastrointestinal tract and it has two important forms: Crohn’s Disease and Ulcerative Colitis. Although the pathophysiology of the disease is mostly unknown, an interaction between the immune system, genetics, microbiome and environmental factors seems to be responsible for the disease onset. The role of environmental factors in the pathophysiology of this disease is reinforced if we consider the rapid growth in incidence and prevalence rates of IBD in areas where the incidence was previously low as, for example, Asia. However, the literature on the role of environmental factors in IBD is reduced and is not systematized. Hence, in this work a Systematic Review of the literature was performed.

Materials and methods: For this systematic review the methodology “Navigation Guide Method for Grading Human Evidence” was used [1]. The research was carried out in three databases (Scopus, Web of Science, PubMed / MEDLINE). The inclusion criteria used were: research articles with original human data, clinically diagnosed inflammatory bowel disease, quantification of environmental contaminants and study of the association between environmental contaminants and inflammatory bowel disease. Only articles written in Portuguese, English, French or Spanish were included.

Results: Sixteen studies were included in this systematic review. Of these, 13 studied Inflammatory Bowel Disease in general, 2 studies included only patients with Crohn’s Disease and 1 study included only patients with Ulcerative Colitis. The most studied environmental contaminants were sulfur dioxide, nitrogen dioxide, carbon monoxide, particulate matter (PM), perfluorooctanoic acid, aluminum, iron, zinc, copper, titanium dioxide, silicates and endotoxins. We also identified different categories of studies, 4 studies on the effects of air pollution, 3 on the intake of contaminated water and 3 on the effects of diet. Additionally, 2 studies evaluated the serum concentrations of contaminants, 1 studied the impact of exposure to house dust, 2 attempted a cell characterization of IBD patients and in another colitis was induced. Overall, the quality of evidence was rated “moderate to low” and the strength of evidence as “Inadequate evidence on toxicity”.

Discussion and conclusions: In this systematic review, we have identified different classes of environmental contaminants associated with IBD, but studies reporting their concentration in biological matrices are rare. Based on a moderate to low level of quality, the available evidence gathered in this Systematic Review is insufficient to access the role of environmental contaminants in inflammatory bowel disease. New epidemiological studies are necessary.

Acknowledgements

The authors acknowledge funding from Projects POCI-01-0145-FEDER-007491, UID/Multi /00709/2013 and CENTRO-01-0145-FEDER-000013. Ana C. Sousa also acknowledges the financial support of Labex DRIIHM (PIA), via OHMI Estarreja – OHM Bassin Minier de Provence, International Observatory Hommes-Millieux, tool of CNRS/INEE - National Center for Scientific Research/Institute of Ecology and Environment, France.