Sedentary time, metabolic abnormalities, and all-cause mortality after myocardial infarction: A mediation analysis

Background Sedentary time was associated with myocardial infarction (MI) and metabolic diseases in previous studies. Purpose To investigate whether sedentary time measured before disease onset was associated with all-cause mortality among MI survivors and whether the sedentary time-mortality association was mediated by physical activity status and metabolic phenotypes. Methods In this prospective community-based cohort including 101,510 Chinese adults, we used sedentary time, evaluated at 2006 (baseline), to predict further all-cause mortality among individuals who then developed new onset MI from 2006 to December 2013 (n = 989). The post-MI mortality was ascertained after the first non-fatal MI until December 2014. We assessed the mediating effects of physical inactivity and metabolic factors on the sedentary time-mortality association. Results During 7 years follow up, 180 deaths occurred among these participants with incident MI. Prolonged sedentary time was associated with a higher risk of mortality among MI survivors. The adjusted hazard ratio (HR) of mortality for sedentary time 4-8 hours/day versus <4 hours/day, was 1.62 (95% confidence interval (CI) 1.14-2.31). A high amount of sedentary time (>4 hours/day) and inactive physical activity had an increased risk of all-cause mortality (HR: 2.74, 95% CI 1.34-5.60), relative to those with sedentary time <= 4 hours/day and moderate/vigorous physical activity. Physical inactivity and metabolic factors mediated a small proportion (<= 9.2 % for all) of the total association between sedentary time and post-MI mortality. Conclusion High sedentary time was significantly associated with all-cause mortality among MI survivors, independent of physical activity status and metabolic abnormalities.