Mortality Effects of Hypothetical Interventions on Physical Activity and TV Viewing

Introduction Long-term effects of physical activity and TV viewing on mortality have been inferred from observational studies. The associations observed do not allow inferences about the effects of population interventions and could be subject to bias due to time-varying confounding. Methods Using data from the Australian Diabetes, Obesity and Lifestyle Study, collected in 1999-2000 (T0), 2004-05 (T1), and 2011-12 (T2), we applied the parametric g-formula to estimate cumulative risks of death under hypothetical interventions on physical activity and/or TV viewing determined from self-report, while adjusting for time-varying confounding. Results In the 6,377 participants followed for 13 years from 2004-05 to death or censoring in 2017, 781 participants died. The observed cumulative risk of death was 12.2%. The most effective hypothetical intervention was to increase weekly physical activity to >300 minutes (RR=0.66, 0.46 to 0.86 compared with a 'worst-case' scenario; and RR=0.83, 0.73 to 0.94 compared with no intervention). Reducing daily TV viewing to Conclusion Our findings suggested that sustained interventions to increase physical activity could lower all-cause mortality over a 13-year period and there might be limited gain from intervening to reduce TV viewing time in a relatively healthy population.