Environmental influences impacting Inflammatory Bowel Diseases (IBD)

After decades of uncertainty European scientists compiled 183 risk assessments from 53 meta-studies for 71 environmental factors influencing chronic inflammatory bowel diseases (IBD), Crohn's disease (CD) and ulcerative colitis (UC).

Nine environmental factors increase the risk of IBD, seven others reduce it

Various environmental influences favor or prevent the onset of chronic inflammatory bowel diseases (IBD), Crohn's disease (CD) and ulcerative colitis (UC). After decades of uncertainty and partly speculative data, European scientists have compiled 183 risk assessments for 71 environmental factors from 53 meta-studies and evaluated them in a meta-analysis of meta-studies ("umbrella study") (source 1).

The research team identified as statistically significant factors that increase the risk of IBD the following:

This finding was contrasted by seven risk-reducing factors:

In addition, the researchers found 11 risk-increasing and 16 risk-reducing factors, each of which was associated with a trend, but did not reach actual significance (p < 0.05) (see Table 1 and source 1).

Study design

The question of which environmental influences promote or prevent IBD has been controversial for decades. However, with their umbrella study, the researchers led by Daniele Piovani from the Department of Biomedical Science at Humanitas University in Milan, Italy, have taken a significant step towards a final clarification of the problem.

Tab. 1: Risk factors for the outbreak of IBD according to disease type and evidence strength (according to source 1)

The studies identified in this way were checked for their quality by the scientists using an evaluation tool (AMSTAR 2) and assigned to one of four quality categories: high, medium, low and critically low. None of the studies used were rated better than "low". This was mostly due to the lack of study protocols. However, the authors noted a more cautious formulation of results published after 2000. Following a comprehensive literature search for the years 1989-2018, the scientists exclusively considered epidemiological metastudies with at least 1,000 participants and a probability of error of p < 0.001 with regard to the risk factors examined. Thus, erroneously false positive findings should be excluded from the outset if possible.

Have we achieved conclusive clarity?

Piovani and his colleagues do not believe that their study can be regarded as final. Too many weaknesses were also found in his study based on a large number of meta-analyses. These include among others:

Nevertheless, the study, which is unique to date, represents further progress in the determination of clinically relevant risk factors of IBD. However, further high-quality prospective studies are necessary to be able to reliably differentiate between causes and consequences of IBD and to assess the strength of individual influencing variables for all patient and ethnic groups.

Source:
1. Piovani D, et al. Environmental Risk Factors for Inflammatory Bowel Diseases: An Umbrella Review of Meta-analyses. Gastroenterology. 2019 Apr 20. pii: S0016-5085(19)36709-5. 
https://www.ncbi.nlm.nih.gov/pubmed/31014995