A Physical Activity and Sitting Time Balance Index and All-Cause Mortality Risk.

Introduction: Achieving a healthier balance of more time spent in physical activity (PA) and less time in sedentary behavior is now widely advocated for achieving multiple health benefits. This study introduces a Physical Activity and Sitting Time Balance Index (PASTBI), a potential risk identification tool addressing the interplay between PA and sedentary behavior; and aims to explore its association with the risk of all-cause mortality in Australian adults.

Methods: This prospective cohort study analyzed the Australian Diabetes, Obesity and Lifestyle Study (AusDiab) data on 5,836 Australian adults. The PASTBI was calculated by dividing the total duration of PA (minutes/day) by the duration of sitting time (ST) (hours/day), both self-reported at baseline (2004-2005). The PASTBI was expressed in quartiles ranging from Q1 - low PA/high ST to Q4 - high PA/low ST. The association between PASTBI and all-cause mortality was explored (in 2022) using the Cox proportional hazards regression models adjusted for socio-demographics, lifestyle factors, waist circumference, and the number of comorbidities.

Results: During 78,406 person-years of follow-up (median follow-up of 14.3 years), there were 885 deaths (15%). In the fully adjusted model, compared to those in the highest PASTBI category (Quartile 4 - high PA/low ST), participants from the lowest PASTBI category (Quartile 1 - low PA/high ST) were at a higher risk of all-cause mortality [HR (95% CI) = 1.47 (1.21-1.79)].

Conclusions: A less favorable balance of time spent in PA and ST (as characterized by a parsimonious PASTBI index approach) was associated with a higher risk of all-cause mortality.