Slow gut transit increases the risk of Alzheimer’s disease: An integrated study of the bi-national cohort in South Korea and Japan and Alzheimer’s disease model mice

•Constipation was associated with an increased risk of Alzheimer’s disease (AD) in the South Korean cohort (discovery cohort, HR, 2.04; 95% CI, 2.01–2.07) and the Japan cohort (validation cohort, HR, 2.82; 95% CI, 2.61–3.05).•Loperamide-treated AD mouse model showed increased amyloid-beta and microglia in the brain with slow gut transit.•Loperamide-treated AD mouse model had increased transcription of genes related to norepinephrine secretion and immune responses and decreased transcription of defense against bacteria in colonic tissue.