Isotemporal substitution analysis of the impact of sedentary behavior and physical activity on depression in Taiwanese older adults: A prospective study

Background and aims: Research has shown that reducing sedentary behavior (SB) and increasing physical activity (PA) can lower depression risk in older adults. However, few studies have investigated the effect of reallocating sedentary time to PA on the incidence of depression in older populations. We examined the longitudinal associations of reallocating SB and PA to each other with the incidence of depression in older adults. Methods: Community-dwelling adults aged 65 years and older, capable of independent walking, were recruited through collaboration with outpatient services of a hospital at baseline (2020) and followed up after one year (2021). Baseline light physical activity (LPA) and moderate-to-vigorous physical activity (MVPA) intensities and SB were assessed using a triaxial accelerometer (GT3X+, ActiGraph). The incidence of depression after one year was identified using the 15-item Geriatric Depression Scale. Isotemporal models were used to estimate associations. Results: A total of 167 participants (52.1% women) were included. Adjusted isotemporal models indicated that reallocating time in SB (OR = 0.27, 95% CI = 0.06, 1.21) and LPA (OR = 0.16, 95% CI = 0.03, 0.98) to MVPA was (marginally) associated with a lower risk of depression; in contrast, a higher risk of depression was found when reallocating MVPA time to SB (OR = 5.21, 95% CI = 0.95, 28.53) and LPA (OR = 6.11, 95% CI = 1.02, 36.63). No statistical evidence of the reallocation from SB to LPA on depressive symptoms. Conclusion: The findings suggest that public health initiatives promoting higher levels of PA with reduced sitting times may decrease the risk of geriatric depression. Clinicians and public health practitioners should consider the thresholds of PA intensity when developing strategies to mitigate depression risk among the older population. These findings require further corroboration by monitoring behavioral changes and clarifying context-specific behaviors in the associations.