# Passive smoking exposure and incidence and disease outcomes of inflammatory bowel disease: a systematic review and meta-analysis

## TL;DR

This study reviews the impact of passive smoking on the risk and outcomes of inflammatory bowel diseases like Crohn's and ulcerative colitis.

## Contribution

The study provides a systematic review and meta-analysis on the effects of passive smoking on inflammatory bowel disease incidence and outcomes.

## Key findings

- Passive smoking during childhood and pregnancy increases the odds of Crohn's disease.
- Passive smoking is linked to complications in ulcerative colitis and hospitalization in Crohn's disease.
- Evidence on medication and surgery needs due to passive smoking remains inconclusive.

## Abstract

Inflammatory bowel disease includes a range of chronic gastrointestinal disorders, most commonly Crohn’s Disease (CD) and ulcerative colitis (UC). This systematic review and meta-analysis aims to evaluate the effect of passive smoking on incidence and disease outcomes of CD and UC.

This review was conducted according to the Preferred Reporting Items for Systematic Review and Meta-Analysis (PRISMA) guidelines. Meta-analysis was performed according to the Meta-analysis of Observational Studies in Epidemiology (MOOSE) guidelines. The literature was systematically searched from inception until May 2025 to identify relevant studies from a range of databases including MEDLINE, CINAHL, Embase, Scopus and Cochrane Library.

The initial search yielded 151 articles, with 32 studies deemed relevant for inclusion. Significant associations with passive smoking exposure were seen in 8 out of 20 studies for increased risk of CD and 3 out of 17 studies for UC. Meta-analysis found that passive smoking during childhood (OR 1.19, 95% CI 1.05–1.35) and exposure to smoking during pregnancy (OR 1.27, 95% CI 1.03–1.55) was associated with increase in odds of CD; however neither exposure was associated with an increased odds of UC. Associations with CD were also not confirmed in sensitivity analysis of higher-quality studies. Passive smoking was associated with disease complications including pouch-itis and backwash-ileitis in UC; while exposure to smoking during pregnancy was associated with hospitalisation and colorectal neoplasia in CD. There is inconclusive evidence surrounding the effects of passive smoking on need for medications and surgery.

Findings of this review highlight the importance of educating on harms of passive smoking.

https://www.crd.york.ac.uk/PROSPERO/view/CRD420251035510.