Associations between the 24-h Activity Daily Cycle and Incident Dementia

Physical activity, sedentary behavior (SB), and sleep all impact the risk of incident dementia, however, engagement in these activities is constrained by the 24-h day. Increasing time spent in one activity necessarily reduces time spent in another, making it difficult to fully understand the implications of current behavioral modification recommendations. This study examines how reallocating time spent among sleep, SB, light physical activity (LPA), and moderate-to-vigorous physical activity (MVPA) within a 24-h day impacts dementia risk in older adults.

The compositional data analysis was conducted on data from 51,314 participants (mean [SD] age, 67.28 [4.30] yr; 53.9% female) from the UK Biobank dataset. Participants wore wrist accelerometers for 1 wk, and sleep, SB, LPA, and MVPA were measured using machine learning techniques. Over an average follow-up period of 6.61 (SD, 1.13) yr, 410 participants were diagnosed with dementia.

Compositional data analysis using Cox proportional hazard models revealed that reallocating 1 h·d -1 to SB from all other behaviors was associated with a 114% increased risk of dementia (hazard ratio, 2.14; 95% confidence interval, 1.43-3.22). Conversely, reallocating 1 h·d -1 to MVPA from other behaviors was associated with a 17% reduction in dementia risk (hazard ratio, 0.83; 95% confidence interval, 0.76-0.91). Reallocations to sleep or LPA were not associated with changes in dementia risk unless they impacted time spent in SB or MVPA.

These findings highlight the critical importance of reducing sedentary time and increasing MVPA to lower dementia risk and suggest that interventions targeting these behaviors may be vital for brain health and dementia prevention.