Microscopic colitis is associated with an increased risk of dementia in a Swedish population

Background The microbiota–gut–brain axis has been implicated in dementia. Yet whether dementia is associated with microscopic colitis (MC), an age‐related inflammatory colonic disease involving gut dysbiosis, remains unknown. Methods Using the nationwide ESPRESSO cohort in Sweden, we compared MC patients histologically diagnosed 1990–2017 and aged ≥30 years to their population‐based comparators and siblings, separately. MC association with incident and prevalent dementia diagnosis, respectively, was investigated in a matched cohort and a matched case‐control design. Findings Following 13,037 MC patients and 61,710 population comparators for a median of ∼10 years, we observed 4674 incident dementia cases (46% were Alzheimer's disease [AD]). During the first 5 years since biopsy, MC was associated with a 19% higher dementia risk (adjusted hazard ratio [aHR]: 1.19; 95% confidence interval [CI]: 1.07–1.32). This short‐term association applied to both AD and vascular dementia and appeared stronger as compared to siblings (aHR: 1.55; 95% CI: 1.22–1.97). After 5 years, it attenuated to null in both comparisons, regardless of dementia subtype. Prior dementia was less prevalent in MC (adjusted odds ratio [aOR]: 0.73; 95% CI: 0.65–0.82). This inverse association was independent from medications commonly prescribed in MC but was not supported by sibling findings (aOR: 1.11; 95% CI: 0.81–1.51). Conclusions MC patients may be more vulnerable to dementia diagnosis in early disease course. The intriguing inverse association between MC and preexisting dementia implies a possible underdiagnosis of MC in demented population and warrants further investigation.