Main Outcomes and Covariates
The endpoint of this study was defined as IBD diagnosis (ICD-9-CMcodes 555 and 556), including UC (ICD-9-CM code 556) and CD (ICD-9-CM code 555). We divided participants into 3 age groups: 20–34 years, 35–49 years, and >50 years. Some IBD-related medical comorbidities, including hypertension (ICD-9-CM codes 401-405), diabetes (ICD-9-CM code 250), hyperlipidemia (ICD-9-CM code 272), cardiovascular disease (ICD-9-CMcodes 430-438), heart failure (ICD-9-CM code 428), chronic obstructive pulmonary disease (ICD-9-CM codes 491, 492, and 496), chronic kidney disease (ICD-9-CM codes 580-589), alcohol-related diseases (ICD-9-CM codes 291, 303, 305.00, 305.01, 305.02, 305.03, 571.0-571.3, 790.3, and V11.3), cirrhosis (ICD-9-CM code 571), and biliary stones (ICD-9-CM code 574), were considered potential confounding factors.