Sedentary behavior and the combination of physical activity associated with dementia, functional disability, and mortality: A cohort study of 90,471 older adults in Japan

Objective: To examine the associations of sedentary behavior (SB) and the combination of moderate-to-vigorous intensity physical activity (MVPA) with dementia, functional disability, and mortality in older adults, and the heterogeneity in different subpopulations. Methods: Nation-wide cohort with 90,471 individuals aged >= 65 years in Japan. SB (<3, 3-<8, and >= 8 h per day [h/d]) and MVPA (0, 0 < MVPA<1, and >= 1 h/d) were measured in 2016. Long-term care registry-based incidence of outcomes was ascertained through 2021. Cox proportional hazard models were performed. Results: Compared with SB < 3 h/d group, SB >= 8 h/d was associated with higher risks of dementia, functional disability, and mortality with hazard ratios (95% confidence interval) of 1.36 (1.22-1.52), 1.32 (1.19-1.48), and 1.31 (1.18-1.45). The combination of MVPA and SB demonstrated a dose-respond trend of increasing risks of dementia, functional disability, and mortality with increased SB and decreased MVPA, where participants who spent no MVPA with SB >= 8 h/d had the highest risks. High MVPA attenuated but didn't eliminate the risks. Participants who spent MVPA >= 1 h/d with SB >= 8 h/d had comparable risks to those who spent no MVPA with SB < 3 h/d. No heterogeneity was found by MVPA levels, sex, education, comorbidity, and depression conditions. Conclusions: Prolonged daily SB was associated with higher risks of dementia, functional disability, and mortality in older adults, regardless of MVPA, sex, education, and chronic conditions. Individuals with high MVPA also face considerable risks when engaging in high SB. High MVPA with high SB revealed a comparable risk to no MVPA with low SB.