OBJECTIVES
Sleep is a lifestyle factor known to influence cognitive decline and dementia risk, while physical activity (PA) has consistently been reported as a protective factor. However, most previous studies have examined these factors independently, and their joint effect remains unclear. In addition, prior studies assessed sleep and PA using self-reported questionnaires, which may be subject to recall and reporting bias. Therefore, this study aimed to evaluate both the independent and joint effects of sleep and PA on dementia incidence objectively assessed using accelerometers.
METHODS
Between 2013 and 2015, a total of 39,067 UK Biobank participants (mean age 69.6 ± 2.9 years; 52.1% women) completed 7-day accelerometer assessments. Sleep duration was categorized as short, normal, and long. While moderate-to-vigorous physical activity (MVPA) was classified into tertiles (low, intermediate, high) and into two groups based on World Health Organization recommendations. We also defined dementia from hospital admission records and national death registries. Cox proportional hazard models were applied to examine the joint associations of sleep and physical activity with dementia risk.
RESULTS
Participants with short duration and low volume of MVPA had the highest risk of dementia (hazard ratio [HR]: 1.69, 95% CI: 1.31-2.19). Similarly, those with short sleep duration who did not meet the recommended level of MVPA (HR: 1.42, 95% CI: 1.11-1.80) showed a significantly increased risk of dementia. Lower sleep efficiency was also associated with a higher risk of dementia (HR: 1.60, 95% CI: 1.11-2.31), particularly among participants with low MVPA.
CONCLUSIONS
Short sleep and low MVPA volume associated with a higher risk of dementia, highlighting the importance of addressing both behaviors in dementia prevention strategies.