Dose-response relationship of physical activity and sedentary time with mortality in people with chronic obstructive pulmonary disease: an analysis of UK biobank accelerometer cohort

BACKGROUND: The COPD guidelines recommend engaging in regular physical activity and reducing sedentary time (ST), but little is known about the optimal or minimal dose of physical activity and ST. This study aimed to quantify the prospective dose-response relationships between daily time spent in moderate to vigorous physical activity (MVPA), light physical activity (LPA), ST and mortality, and examine the theoretical consequences of replacing ST with equal time of MVPA or LPA. METHODS: A population-based cohort study of 1,551 individuals with COPD enrolled in the UK Biobank. MVPA, LPA, ST were measured with the wrist-worn Axivity AX3 accelerometer. All-cause mortality was obtained through the linkage to death registries. Restricted cubic splines were used to assess the dose response associations of MVPA, LPA, ST and all-cause mortality. Isotemporal substitution models were used to estimate the theoretical effect of replacing ST with MVPA or LPA. RESULTS: 54% were male, and the mean (SD) age was 66.31 (6.52) years. Over a mean (SD) follow-up of 7.44 (1.67) years, 244 (15.7%) died. We observed a significant L-shaped association between MVPA and all-cause mortality, with an optimal amount at 60 min/day (HR = 0.27, 95% CI: 0.18-0.41). For LPA, we observed a significant U-shaped association, with an optimal amount at 5.2 h/day (HR = 0.15, 95% CI: 0.10-0.25). The threshold for ST was 12.43 h/day, above which a significant increase in mortality was observed. Replacing 30 min/day of ST was associated with 34% decreased risk in mortality for MVPA (HR = 0.66, 95%CI: 0.55-0.81, P < .001) and 10% lower mortality for LPA (HR = 0.90, 95% CI: 0.86-0.94, P < .001). CONCLUSIONS: The findings of this study suggest non-linear associations of MVPA, LPA, ST and all-cause mortality. Replacing ST with either MVPA or LPA is associated with decreased risk of mortality.