Cognitive frailty may be a preventive or therapeutic target for preventing dementia and functional decline with age.

To examine the relationship between physical and cognitive frailty and the incidence of dementia in community-living older persons.

A prospective cohort study. Setting: General community in Japan. Participants: A total of 4072 persons aged ≥ 65 years.

A community in Japan.

A total of 4072 community-dwelling older persons aged ≥ 65 years participated in the study.

We characterized physical frailty as ≥ 3 of the following criteria: slow walking speed, muscle weakness, exhaustion, low physical activity, and weight loss. We used the National Center for Geriatrics and Gerontology-Functional Assessment Tool, which includes tests of word list memory, attention, and executive function, and processing speed to screen for cognitive frailty. The presence of ≥ 2 cognitive impairments, indicated by an age-adjusted score of at least 1.5 standard deviations below the reference threshold, was defined as cognitive frailty. The incidence of dementia was determined using data collected by the Japanese Health Insurance System over 24 months.

The overall prevalence rates of physical frailty, cognitive impairment, and cognitive frailty (i.e., coexistence of frailty and cognitive impairment) were 5.1%, 5.5%, and 1.1%, respectively. During the follow-up period, 81 participants (2.0%) developed dementia. We found significant relationships between the incidence of dementia and cognitive impairment (hazard ratio (HR): 3.85, 95% confidence interval (95% CI): 2.09–7.10) and cognitive frailty (HR: 6.19, 95% CI: 2.7–13.99). However, the association between dementia and physical frailty did not reach significance (HR: 1.95, 95% CI: 0.97–3.91).

Individuals with cognitive frailty had the highest risk of dementia. Future research should implement dementia prevention strategies among older persons with cognitive frailty.