Dietary, lifestyle, and environmental factors associated with ulcerative colitis: a systematic review and meta-analysis of observational studies.

BACKGROUND AND AIMS: Ulcerative colitis (UC) is increasing worldwide, and dietary, lifestyle, and environmental exposures may contribute to disease susceptibility. This systematic review and meta-analysis evaluated the associations between these exposures and the risk of incident UC.

METHODS

PubMed, Embase, and the Cochrane Library were searched for observational studies examining dietary, lifestyle, medication-related, surgical, early-life, sociodemographic, and other environmental exposures in relation to UC risk through November 12, 2025. Random-effects models were used to pool effect estimates. Study quality was assessed using the Newcastle-Ottawa Scale, and the certainty of evidence was evaluated using GRADE.

RESULTS

Thirty observational studies involving 148,468 patients with UC were included, covering 17 factors and 27 comparisons. Daily egg consumption, family history of inflammatory bowel disease, the highest reported category of antibiotic exposure, ever smoking, and former smoking were associated with increased UC risk. Pet exposure, coffee consumption, appendectomy, higher educational attainment, light alcohol consumption, and fruit intake were associated with reduced UC risk. Current smoking was associated with a lower risk of UC in case-control studies, whereas the association was not statistically significant in cohort studies. Adjusted estimates suggested that breastfeeding might be associated with a lower risk of UC, although the evidence was limited. No clear associations were observed for body mass index, oral contraceptive use, tonsillectomy, previous gastrointestinal infection, place of residence, any antibiotic use, tea consumption, or heavy alcohol consumption.

CONCLUSION

Dietary, lifestyle, and broader environmental factors showed different directions of association with UC risk, although the overall certainty of evidence was low. These findings support further prospective and mechanistic studies to clarify causal pathways and identify potentially modifiable exposures relevant to UC prevention.

SYSTEMATIC REVIEW REGISTRATION: PROSPERO, CRD420261343412.