Association between sitting-time and all-cause mortality in the multiethnic cohort study

Abstract

It has been proposed recently that time spent sitting increases total mortality, but evidence to support this hypothesis, especially for various ethnic group, is limited. We examined the relationship between sitting time (hr/d) and mortality not including sitting time during working, and overall by ethnic group in the Multiethnic Cohort (MEC). The MEC is a prospective study of chronic diseases and lifestyle factors that recruited over 215,000 adults (ages 45-75) between 1993-1996, mainly representing five ethnic groups: African Americans, Latinos, Japanese Americans, Native Hawaiians and Whites. For this analysis, only the 71,067 men and 81,423 women of the five main ethnic groups who had no missing data for exposures and confounders were included. Median follow-up was 11.6 years and 21,177 deaths were identified. Cox proportional hazards regression, with age as the time metric, was used to estimate the risk of mortality, after adjusting for potential confounders (including age, ethnicity as appropriate, smoking, education, obesity, alcohol consumption, and physical activity). Compared to sitting less than 4 hours, sitting more than 8 hours per day not including sitting time at work increased the risk of total mortality by 15% (Hazard Ratio (HR) 1.15, 95% Confidence Interval (CI) 1.09-1.22) in men, and by 18% (HR 1.18, 95% CI 1.11-1.26) in women. When the results were stratified by sex and ethnicity, all groups showed a positive relationship between sitting time and mortality. In conclusion, these findings suggest that the extent of leisure time spent sitting can have an adverse effect on overall mortality, independent of the level of physical activity.