Study population
The Nakajima study is an ongoing population-based longitudinal cohort study that investigates cognitive decline in older Japanese individuals. The study was conducted in Nakajima, in Nanao City of Ishikawa Prefecture, Japan. The study design has been described previously21. From 2016 to 2018, a total of 2454 residents aged 60 years or older (92.9% of the total population in this age group) participated in the screening examination for dementia. To clarify whether frailty is a risk factor for cognitive impairment among cognitively unimpaired older adults, we excluded patients with dementia (n = 364) and MCI (n = 427). MCI and dementia were confirmed using the clinical criteria defined by Petersen et al.22 and the Third Diagnostic and Statistical Manual of Mental Disorders, Revised Edition (DSM-III-R)23. We also excluded individuals who had hemorrhagic and/or…
