The sample included 1,005,791 individuals followed between 2-18 years during which 84,609 (8.4%) died. There was a clear dose response association of increased risk of mortality with increased sitting time in combination with low activity level. Compared to the control group (those sitting < 4 hours a day and in the most active quartile), mortality during follow up was 12-59% higher in the two lowest quartiles of physical activity (HR=1.12, 95% CI 1.08-1.16, for the second lowest quartile of physical activity and <4 hours a day of sitting time, HR =1.59, 1.52-1.66 for the lowest quartile of physical activity and > 8 hours/day of sitting time).
Those in the most active quartile but also sitting the most (>8 hours /day) had a significantly lower risk (p<0.0001) of dying during follow up (HR= 1.04; 95% CI 0.99-1.10) than the least active (< 4 hours /day, HR= 1.27,1.22-1.30). The analyses for TV-viewing time was not as precise due to a smaller sample size. For those who watched TV for five or more hours per day, the hazard for all-cause mortality was increased markedly from 16% to 93% across all activity quartiles. In the most active quartile only, watching TV five hours a day was significantly associated with increased mortality (HR 1.16, 95% CI 1.05—1,28). Those in the least active quartile who watched TV for < 1 h/day had a higher mortality risk (HR 1.32, 1.20—1.46; p=0.007)