Association between various sedentary behaviours and all-cause, cardiovascular disease and cancer mortality: the Multiethnic Cohort Study

Background It has been proposed that time spent sitting increases all-cause mortality, but evidence to support this hypothesis, especially the relative effects of various sitting activities alone or in combination, is very limited. Methods The association between various sedentary behaviours (time spent: sitting watching television (TV); in other leisure activities; in a car/bus; at work; and at meals) and mortality (all-cause and cause-specific) was examined in the Multiethnic Cohort Study, which included 61 395 men and 73 201 women aged 45-75 years among five racial/ethnic groups (African American, Latino, Japanese American, Native Hawaiian and White) from Hawaii and Los Angeles, USA. Results Median follow-up was 13.7 years and 19 143 deaths were recorded. Total daily sitting was not associated with mortality in men, whereas in women the longest sitting duration (epsilon 10 h/day vs < 5 h/day) was associated with increased all-cause (11%) and cardiovascular (19%) mortality. Multivariate hazard ratios (HR) for epsilon 5 h/day vs < 1 h/day of sitting watching TV were 1.19 in men (95% confidence interval (CI) 1.10-1.29) and 1.32 in women (95% CI 1.21-1.44) for all-cause mortality. This association was consistent across four racial/ethnic groups, but was not seen in Japanese Americans. Sitting watching TV was associated with an increased risk for cardiovascular mortality, but not for cancer mortality. Time spent sitting in a car/bus and at work was not related to mortality. Conclusions Leisure time spent sitting, particularly watching television, may increase overall and cardiovascular mortality. Sitting at work or during transportation was not related to mortality.