Associations of objectively measured physical activity and sedentary time with all-cause mortality in Japanese older adults: a 10-year prospective study

Objective: To examine the associations of accelerometer-measured physical activity and sedentary time with all-cause mortality in older Japanese adults. Methods: A total of 1723 independent Japanese adults aged ≥65 years were followed from 2011 to 2021. Moderate-to-vigorous physical activity (MVPA), light physical activity (LPA) and sedentary time were measured using a triaxial accelerometer secured to participants' waists. Results: Over a median follow-up of 9.9 years, 336 deaths were recorded. When examined as tertiles, higher MVPA (both ≥10 and <10 min bouts) and LPA were associated with a lower mortality risk. Additional adjustment for MVPA attenuated the associations of LPA, but the HRs in the highest tertile remained significant. Longer sedentary time was significantly associated with an increased mortality risk, but not after adjusting for MVPA. In spline analyses, a linear dose-response association with all-cause mortality was observed for LPA, while the HRs declined progressively with higher levels of MVPA until approximately 80 min/day, beyond which they levelled out. Replacing 10 min/day of sedentary time with MVPA but not LPA was associated with a 12% lower risk of morality (HR 0.88; 95% CI 0.83 to 0.93); the HR for replacing 10 min/day LPA with MVPA was 0.89 (95% CI 0.84 to 0.95). These results were materially unchanged when excluding deaths within the first 5 years of follow-up. Conclusion: Physical activity, regardless of intensity, was associated with a lower all-cause mortality risk among older Japanese adults. Replacing sedentary time or LPA with MVPA was associated with a lower mortality risk. The mortality benefit started from a low MVPA dose and additional benefits were associated with higher doses.