Independent and interactive effect of sedentary time and physical activity on risk of all-cause mortality: A prospective cohort study.

OBJECTIVES: Sedentary behavior (SB) and physical inactivity have been associated with an increased risk of all-cause mortality. Evidence in China is scarce, and it is unclear whether physical activity (PA) attenuates or even eliminates the harmful effects of prolonged SB in the Chinese population.

METHODS: We conducted a prospective cohort study of 17 084 Chinese adults. PA and sitting time (ST) were assessed using the IPAQ. Cox proportional hazards models were used to estimate the risk of PA and ST with all-cause mortality. Interaction plots were used to visualize the interaction effects.

RESULTS: During a median follow-up of 6.01 years, a total of 1106 deaths occurred. PA level was inversely associated with the incidence of all-cause mortality, while ST showed a detrimental association (all ptrend  < 0.05). In the stratified analysis, ST was associated with all-cause mortality in the low PA, while the association was attenuated in the moderate PA group: the HRs (95% CI) comparing ST of 4-8, 8-11, and ≥11 to <4 h/day were 1.15 (0.73-1.81), 1.55 (0.92-2.59), and 2.70 (1.52-4.80), respectively. In the high PA group, no significant association was found across all ST levels. In the joint analysis, compared with the high PA and ST <4 h/day, the harmful effect was found only in the combined low PA and moderate PA groups with ST ≥11 h/day (HR:2.71, 95% CI:1.69-4.35). In addition, a significant interaction association was found.

CONCLUSION: Our study, based on a prospective cohort, suggests that the detrimental effect of ST on all-cause mortality is attenuated or eliminated by high PA levels in the Chinese population.