Association between activity levels and sleep in Community-Dwelling older adults: Insights from a dementia prevention trial using wearable devices

Background Changes in sleep patterns are a risk factor for dementia in older adults. This secondary, exploratory analysis of the Japan-Multimodal Intervention Trial Prime Kanagawa for the Prevention of Dementia (J-MINT Prime Kanagawa) investigated the observational associations between physical activity and sleep architecture using wearable devices. Methods In this open-label, randomized controlled trial, 198 individuals (aged ≥65 years) at risk for cardiometabolic comorbidities were assigned to a multimodal intervention or a control group. Daily step counts, activity levels, and sleep characteristics—including proportions of deep non-rapid eye movement (NREM), light NREM, and rapid eye movement (REM) sleep—were measured using a wrist-worn Fitbit® Inspire HR at 6, 12, and 18 months. Results Daily step counts and activity levels were significantly higher in the intervention group compared with the control group. Although no significant intergroup differences were observed in sleep architecture, multiple regression analysis using pooled data revealed that an increase in daily step counts was significantly associated with a higher proportion of deep NREM sleep. Additionally, Fitbit-measured sleep duration, rather than self-reported duration, showed a significant association with the proportion of REM sleep. Conclusions Higher levels of physical activity would be associated with better sleep quality in older adults at risk for cardiometabolic comorbidities. Objective monitoring using wearable devices provides more reliable insights than self-reports and is feasible for tracking intermediate biomarkers of dementia risk, though further research in larger populations is required to validate these findings. Trial registration UMIN000041887 (Registered on 2020/09/24).