The association between artificial light at night and inflammatory bowel disease incidence, surgery, and health services utilization: population-based observational studies

INTRODUCTION: The urban environment increases the risk of inflammatory bowel disease (IBD). Specific environmental exposures involved in IBD etiology remain unknown. We examined the association between outdoor artificial light at night (ALAN) and IBD incidence, surgery, and health services utilization (HSU). METHODS: Using population-based deterministically linked health administrative data from Ontario, Canada we conducted a birth cohort study (incidence), matched case-control study (incidence), and cohort study (surgery, HSU). Individuals with IBD were identified using previously validated algorithms. ALAN, the average digital number of lights consistently present, was a 3-level variable: <35 (reference), 35-60, > 60. We used Cox proportional hazards models (birth cohort, surgery), conditional logistic regression (matched case-control study), and Poisson regression (HSU). RESULTS: Among 3 929 374 individuals in the birth cohort, 5539 (0.1%) developed IBD; no association between ALAN at birth and IBD was observed (35-60: hazard ratio [HR] 1.03, 95% confidence interval [CI] 0.87-1.22; >60: HR 0.93, 95% CI 0.78-1.11). Among 32 176 IBD cases matched to 160 709 controls, high ALAN was associated with a lower IBD risk (>60: odds ratio [OR] 0.84, 95% CI 0.78-0.92); there was no association between IBD and the middle ALAN level. High ALAN was associated with fewer IBD-specific outpatient visits (rate ratio [RaR] 0.93, 95% CI 0.86-0.99) and hospitalizations (RaR 0.83, 95% CI 0.72-0.95) 1 year after diagnosis. ALAN was not associated with surgery or emergency department visits. DISCUSSION: The association between ALAN and IBD is heterogeneous. Additional research is needed to understand how ALAN impacts IBD and identify other environmental exposures contributing to IBD etiology.