Exposure to particulate matter less than 2.5 microns (PM2.5) and airborne toxic releases from industrial facilities is associated with the incidence of irritable bowel syndrome (IBS), according to a study in Clinical Gastroenterology and Hepatology.
Researchers sought to quantify associations among several air pollutants, water contaminants, and the incidence of IBS, functional dyspepsia (FD), ulcerative colitis (UC), Crohn disease (CD), and eosinophilic esophagitis (EoE) in a large cohort of individuals.
Data were obtained from the Clinformatics Data Mart Database (CDM), which includes commercially insured California residents. Participants aged over 18 years with 1 of the gastrointestinal diseases were identified from January 1, 2009, to December 31, 2014 (International Classification of Diseases, 9th Revision [ICD-9] era), and from January 1, 2016, to December 31, 2019 (ICD-10 era).
Log-linear negative binomial regression models were used to estimate adjusted incidence rate ratios (aIRR) for each disease associated with a single unit increase in each environmental exposure, which included ozone, PM2.5, diesel particulate matter, drinking water contaminants, pesticide use, toxic releases from facilities, and traffic density.
The cohort included health care claims from about 2.9 million patients in 1365 distinct zip codes. In the ICD-9 era, the estimated incidences of FD, IBS, UC, CD, and EoE were 0.65, 0.56, 0.16, 0.10, and 0.02, respectively, per 100 person-years. In the ICD-10 era, the estimated incidences of FD, IBS, UC, CD, and EoE were 0.29, 0.55, 0.15, 0.08, and 0.04, respectively, per 100 person-years.
Variation in disease incidence was observed across zip codes, although no clear geographic pattern was evident. The estimated proportion of variation in disease incidence accounted for with county-level clustering ranged from 9% (EoE) to 16% (CD and FD). Substantial variation in environmental exposure occurred across zip codes. Clear geographic clustering was found, particularly for ozone variation, in which county variation accounted for 88.1% of the total variation.
IBS was the only disease to have a significant association with pollutants in both eras (PM2.5 and airborne toxic releases from facilities, P <.001 for both). No consistent, significant association was found for FD, UC, CD, EoE, or the negative control with any of the pollutants in both eras, after adjustment for multiple comparisons.
In the ICD-9 and ICD-10 groups, increasing PM2.5 and airborne toxic releases (log-transformed) were modestly, but significantly, associated with IBS incidence at the zip-code level. PM2.5 had an aIRR of 1.032 (95% CI, 1.019-1.045) in the ICD-9 era and 1.025 (95% CI, 1.012-1.039) in the ICD-10 era. Toxic releases had an aIRR of 1.037 (95% CI, 1.024-1.050) in the ICD-9 era and 1.027 (95% CI, 1.013-1.041) in the ICD-10 era. The aIRRs were about 1.03, which indicates that an increase of either 1 microgram/m3 of PM2.5 or 1% in airborne toxic releases is associated with about a 3% increase in the incidence of IBS.
Drinking water contaminants and traffic density were significantly associated with IBS incidence in the ICD-9 era only. PM2.5 exposure, drinking water contaminants, and log-transformed airborne toxic releases from facilities were significantly associated with FD incidence only in the ICD-10 era.
Study limitations include the inability to assess individual-level exposures and relying on CDM health care claims data as a result. Also, the study did not assess seasonality in exposures or consider the interactive effects of multiple pollutants. Furthermore, census tract/zip code cigarette smoking data were lacking.
“We find evidence of an association between PM2.5 and airborne toxic releases from industrial facilities and IBS, warranting further confirmatory epidemiologic and mechanistic studies to evaluate the role of these exposures in IBS development,” the study authors noted.
Okafor PN, Dahlen A, Youssef M, et al. Environmental pollutants are associated with irritable bowel syndrome in a commercially insured cohort of California residents. Clin Gastroenterol Hepatol. Published online October 3, 2022. doi: 10.1016/j.cgh.2022.09.025