Association of Hormone Replacement Therapy with Inflammatory Bowel Disease Risk in Women with Menopausal Disorders: A Population-Based Retrospective Cohort Study

<b>Background</b>: The long-term effects of hormone replacement therapy (HRT) on inflammatory bowel disease (IBD) remain unclear, necessitating further investigations of the association between HRT and the development of ulcerative colitis and Crohn's disease in postmenopausal women. <b>Methods</b>: This retrospective cohort study utilized Taiwan's National Health Insurance claims (2001-2018) to identify postmenopausal women aged ≥ 50 years with HRT use. A one-year washout period was applied before the index date to ensure new HRT users. To address the immortal time bias, follow-up for HRT users began at HRT initiation. The non-HRT group was selected by 1:1 propensity score matching. Cox proportional hazards models with adjustments for comorbidities and medications were used to estimate hazard ratios. <b>Results</b>: A total of 10,126 postmenopausal women (5063 per group) were included. During a mean follow-up of 11.1 years, the incidence rates of ulcerative colitis were 0.14 and 0.11 per 1000 person-years in the HRT and non-HRT groups, respectively. The adjusted hazard ratios were 1.33 (95% CI, 0.46-3.83; <i>p</i> = 0.600) for ulcerative colitis and 0.72 (95% CI, 0.45-1.16; <i>p</i> = 0.177) for Crohn's disease. <b>Conclusions</b>: This longitudinal study suggests that HRT use is not significantly associated with the risk of IBD among postmenopausal women. These findings indicate that IBD risk may not need to be a primary concern when considering HRT in this population.