The Role of Environmental Factors Prior to Diagnosis on the Activity and Severity of Inflammatory Bowel Diseases-Results From the Prospective Population-Based Copenhagen Inflammatory Bowel Disease Inception Cohort.

Background: The influence of environmental factors on the severity of early inflammatory bowel disease (IBD), including ulcerative colitis (UC) and Crohn's disease (CD), is unclear. Herein, we aimed to investigate the role of environmental factors in the initial phenotype, activity, and severity of IBD.

Methods: Copenhagen IBD Inception Cohort is a prospective population-based cohort of patients with newly diagnosed IBD between May 2021 and May 2023. Data on environmental factors were captured at IBD diagnosis using International Organisation of IBD (IOIBD) and HeartDiet questionnaires. Environmental factors' influence on outcome was analyzed and odds ratios (aOR) were adjusted for age, gender, and disease characteristics (adjusted OR, aOR [95% confidence interval]).

Results: In total, 208 and 128 patients with incident UC and CD, respectively, were included. Active smoking was associated with increased risk of CD-related hospitalization (aOR = 2.84 [1.03; 7.88]) and stricturing phenotype (aOR = 5.28 [1.76; 15.85]) but lower risk of severe UC course (aOR = 0.28 [0.08; 0.95]). Further, previous smoking was not associated with negative effects in patients with CD in terms of early need for biologics, surgery, or hospitalization. In terms of diets, daily consumption of fruits (aOR = 0.27 [0.07; 0.99]) or vegetables (aOR = 0.27 [0.09; 0.80]) was inversely associated with stricturing CD, whereas whole meal bread was associated with reduced risk of severe CD activity (aOR = 0.40 [0.16; 0.98]).

Conclusions: This prospective population-based study highlighted several environmental factors associated with the initial severity and activity of IBD, emphasizing their pivotal role in the initial disease burden and giving guidance to personalized patient counseling.